Astronomy Picture of the Day Search Results for "Aurora"

APOD: 2024 February 25 – A Phoenix Aurora over Iceland
Explanation: All of the other aurora watchers had gone home. By 3:30 am in Iceland, on a quiet September night, much of that night's auroras had died down. Suddenly, unexpectedly, a new burst of particles streamed down from space, lighting up the Earth's atmosphere once again. This time, surprisingly, pareidoliacally, the night lit up with an amazing shape reminiscent of a giant phoenix. With camera equipment at the ready, two quick sky images were taken, followed immediately by a third of the land. The mountain in the background is Helgafell, while the small foreground river is called Kaldá, both located about 30 kilometers north of Iceland's capital Reykjavík. Seasoned skywatchers will note that just above the mountain, toward the left, is the constellation of Orion, while the Pleiades star cluster is also visible just above the frame center. The 2016 aurora, which lasted only a minute and was soon gone forever -- would possibly be dismissed as a fanciful fable -- were it not captured in the featured, digitally-composed, image mosaic.

APOD: 2024 January 18 - Northern Lights from the Stratosphere
Explanation: Northern lights shine in this night skyview from planet Earth's stratosphere, captured on January 15. The single, 5 second exposure was made with a hand-held camera on board an aircraft above Winnipeg, Canada. During the exposure, terrestrial lights below leave colorful trails along the direction of motion of the speeding aircraft. Above the more distant horizon, energetic particles accelerated along Earth's magnetic field at the planet's polar regions excite atomic oxygen to create the shimmering display of Aurora Borealis. The aurora's characteristic greenish hue is generated at altitudes of 100-300 kilometers and red at even higher altitudes and lower atmospheric densities. The luminous glow of faint stars along the plane of our Milky Way galaxy arcs through the night, while the Andromeda galaxy extends this northern skyview to extragalactic space. A diffuse hint of Andromeda, the closest large spiral to the Milky Way, can just be seen to the upper left.

APOD: 2024 January 14 – Dragon Aurora over Iceland
Explanation: Have you ever seen a dragon in the sky? Although real flying dragons don't exist, a huge dragon-shaped aurora developed in the sky over Iceland in 2019. The aurora was caused by a hole in the Sun's corona that expelled charged particles into a solar wind that followed a changing interplanetary magnetic field to Earth's magnetosphere. As some of those particles then struck Earth's atmosphere, they excited atoms which subsequently emitted light: aurora. This iconic display was so enthralling that the photographer's mother ran out to see it and was captured in the foreground. Our active Sun continues to show an unusually high number of prominences, filaments, sunspots, and large active regions as solar maximum approaches in 2025.

APOD: 2024 January 3 – A SAR Arc from New Zealand
Explanation: What is that unusual red halo surrounding this aurora? It is a Stable Auroral Red (SAR) arc. SAR arcs are rare and have only been acknowledged and studied since 1954. The featured wide-angle photograph, capturing nearly an entire SAR arc surrounding more common green and red aurora, was taken earlier this month from Poolburn, New Zealand, during an especially energetic geomagnetic storm. Why SAR arcs form remains a topic of research, but is likely related to Earth's protective magnetic field, a field created by molten iron flowing deep inside the Earth. This magnetic field usually redirects incoming charged particles from the Sun's wind toward the Earth's poles. However, it also traps a ring of ions closer to the equator, where they can gain energy from the magnetosphere during high solar activity. The energetic electrons in this ion ring can collide with and excite oxygen higher in Earth's ionosphere than typical auroras, causing the oxygen to glow red. Ongoing research has uncovered evidence that a red SAR arc can even transform into a purple and green STEVE.

APOD: 2023 December 27 – Rainbow Aurora over Icelandic Waterfall
Explanation: Yes, but can your aurora do this? First, yes, auroras can look like rainbows even though they are completely different phenomena. Auroras are caused by Sun-created particles being channeled into Earth's atmosphere by Earth's magnetic field, and create colors by exciting atoms at different heights. Conversely, rainbows are created by sunlight backscattering off falling raindrops, and different colors are refracted by slightly different angles. Unfortunately, auroras can’t create waterfalls, but if you plan well and are lucky enough, you can photograph them together. The featured picture is composed of several images taken on the same night last November near the Skógafoss waterfall in Iceland. The planning centered on capturing the central band of our Milky Way galaxy over the picturesque cascade. By luck, a spectacular aurora soon appeared just below the curving arch of the Milky Way. Far in the background, the Pleiades star cluster and the Andromeda galaxy can be found.

APOD: 2023 December 23 - A December Summer Night
Explanation: Colours of a serene evening sky are captured in this 8 minute exposure, made near this December's solstice from New Zealand, southern hemisphere, planet Earth. Looking south, star trails form the short concentric arcs around the rotating planet's south celestial pole positioned just off the top of the frame. At top and left of center are trails of the Southern Cross stars and a dark smudge from the Milky Way's Coalsack Nebula. Alpha and Beta Centauri make the brighter yellow and blue tinted trails, reflected below in the waters of Hoopers Inlet in the Pacific coast of the South Island's Otago Peninsula. On that short December summer night, aurora australis also gave luminous, green and reddish hues to the sky above the hills. Aurora shine as atoms and molecules in the upper atmosphere are excited by collisions with energetic particles. An upper atmospheric glow distinct from the aurora, a pale greenish airglow caused by a cascade of chemical reactions excited by sunlight, can be traced in diagonal bands at top left.

APOD: 2023 December 12 – Aurora and Milky Way over Norway
Explanation: What are these two giant arches across the sky? Perhaps the more familiar one, on the left, is the central band of our Milky Way Galaxy. This grand disk of stars and nebulas here appears to encircle much of the southern sky. Visible below the stellar arch is the rusty-orange planet Mars and the extended Andromeda galaxy. But this night had more! For a few minutes during this cold arctic night, a second giant arch appeared encircling part of the northern sky: an aurora. Auroras are much closer than stars as they are composed of glowing air high in Earth's atmosphere. Visible outside the green auroral arch is the group of stars popularly known as the Big Dipper. The featured digital composite of 20 images was captured in mid-November 2022 over the Lofoten Islands in Norway.

APOD: 2023 November 25 - Little Planet Aurora
Explanation: Immersed in an eerie greenish light, this rugged little planet appears to be home to stunning water falls and an impossibly tall mountain. It's planet Earth of course. On the night of November 9 the nadir-centered 360 degree mosaic was captured by digital camera from the Kirkjufell mountain area of western Iceland. Curtains of shimmering Aurora Borealis or Northern Lights provide the pale greenish illumination. The intense auroral display was caused by solar activity that rocked Earth's magnetosphere in early November and produced strong geomagnetic storms. Kirkjufell mountain itself stands at the top of the stereographic projection's circular horizon. Northern hemisphere skygazers will recognize the familiar stars of the Big Dipper just above Kirkjufell's peak. At lower right the compact Pleiades star cluster and truly giant planet Jupiter also shine in this little planet's night sky.

APOD: 2023 November 6 – Red Aurora over Italy
Explanation: What was that red glow on the horizon last night? Aurora. Our unusually active Sun produced a surface explosion a few days ago that sent out a burst of electrons, protons, and more massive charged nuclei. This coronal mass ejection (CME) triggered auroras here on Earth that are being reported unusually far south in Earth's northern hemisphere. For example, this was the first time that the astrophotographer captured aurora from her home country of Italy. Additionally, many images from these auroras appear quite red in color. In the featured image, the town of Comelico Superiore in the Italian Alps is visible in the foreground, with the central band of our Milky Way galaxy seen rising from the lower left. What draws the eye the most, though, is the bright red aurora on the far right. The featured image is a composite with the foreground and background images taken consecutively with the same camera and from the same location.

APOD: 2023 November 5 – Creature Aurora Over Norway
Explanation: It was Halloween and the sky looked like a creature. Exactly which creature, the astrophotographer was unsure (but possibly you can suggest one). Exactly what caused this eerie apparition in 2013 was sure: one of the best auroral displays that year. This spectacular aurora had an unusually high degree of detail. Pictured here, the vivid green and purple auroral colors are caused by high atmospheric oxygen and nitrogen reacting to a burst of incoming electrons. Birch trees in Tromsø, Norway formed an also eerie foreground. Frequently, new photogenic auroras accompany new geomagnetic storms.

APOD: 2023 October 22 – Ghost Aurora over Canada
Explanation: What does this aurora look like to you? While braving the cold to watch the skies above northern Canada early one morning in 2013, a most unusual aurora appeared. The aurora definitely appeared to be shaped like something, but what? Two ghostly possibilities recorded by the astrophotographer were "witch" and "goddess of dawn", but please feel free to suggest your own Halloween-enhanced impressions. Regardless of fantastical pareidolic interpretations, the pictured aurora had a typical green color and was surely caused by the scientifically commonplace action of high-energy particles from space interacting with oxygen in Earth's upper atmosphere. In the image foreground, at the bottom, is a frozen Alexandra Falls, while evergreen trees cross the middle.

APOD: 2023 July 30 – Spiral Aurora over Icelandic Divide
Explanation: Admire the beauty but fear the beast. The beauty is the aurora overhead, here taking the form of a great green spiral, seen between picturesque clouds with the bright Moon to the side and stars in the background. The beast is the wave of charged particles that creates the aurora but might, one day, impair civilization. In 1859, following notable auroras seen all across the globe, a pulse of charged particles from a coronal mass ejection (CME) associated with a solar flare impacted Earth's magnetosphere so forcefully that it created the Carrington Event. This assault from the Sun compressed the Earth's magnetic field so violently that it created high currents and sparks along telegraph wires, shocking many telegraph operators. Were a Carrington-class event to impact the Earth today, speculation holds that damage might occur to global power grids and electronics on a scale never yet experienced. The featured aurora was imaged in 2016 over Thingvallavatn Lake in Iceland, a lake that partly fills a fault that divides Earth's large Eurasian and North American tectonic plates.

APOD: 2023 July 4 – Aurora over Icelandic Waterfall
Explanation: It seemed like the sky exploded. The original idea was to photograph an aurora over a waterfall. After waiting for hours under opaque clouds, though, hope was running out. Others left. Then, unexpectedly, the clouds moved away. Suddenly, particles from a large solar magnetic storm were visible impacting the Earth's upper atmosphere with full effect. The night sky filled with colors and motion in a thrilling auroral display. Struggling to steady the camera from high Earthly winds, the 34 exposures that compose the featured image were taken. The resulting featured composite image shows the photogenic Godafoss (Goðafoss) waterfall in northern Iceland in front of a very active aurora in late February. The solar surface explosion that expelled the energetic particles occurred a few days before. Our Sun is showing an impressive amount of surface activity as it approaches solar maximum, indicating that more impressive auroras are likely to appear in Earth's northern and southern sky over the next few years.

APOD: 2023 July 2 – Milky Way and Aurora over Antarctica
Explanation: It was one of the better skies of this long night. In parts of Antarctica, not only is it winter, but the Sun can spend weeks below the horizon. At China's Zhongshan Station, people sometimes venture out into the cold to photograph a spectacular night sky. The featured image from one such outing was taken in mid-July of 2015, just before the end of this polar night. Pointing up, the wide angle lens captured not only the ground at the bottom, but at the top as well. In the foreground, a colleague is taking pictures. In the distance, a spherical satellite receiver and several windmills are visible. Numerous stars dot the night sky, including Sirius and Canopus. Far in the background, stretching overhead from horizon to horizon, is the central band of our Milky Way Galaxy. Even further in the distance, visible as extended smudges near the top, are the Large and Small Magellanic Clouds, satellite galaxies near our huge Milky Way Galaxy.

APOD: 2023 April 25 – Northern Lights over Southern Europe
Explanation: Did you see an aurora over the past two nights? Many people who don't live in Earth's far north did. Reports of aurora came in not only from northern locales in the USA as Alaska, but as far south as Texas and Arizona. A huge auroral oval extended over Europe and Asia, too. Pictured, an impressively red aurora was captured last night near the town of Cáceres in central Spain. Auroras were also reported in parts of southern Spain. The auroras resulted from a strong Coronal Mass Event (CME) that occurred on the Sun a few days ago. Particles from the CME crossed the inner Solar System before colliding with the Earth's magnetosphere. From there, electrons and protons spiraled down the Earth's northern magnetic field lines and collided with oxygen and nitrogen in Earth's atmosphere, causing picturesque auroral glows. Our unusually active Sun may provide future opportunities to see the northern lights in southern skies.

APOD: 2023 April 19 – Auroral Storm over Lapland
Explanation: On some nights the sky is the best show in town. On this night, auroras ruled the sky, and the geomagnetic storm that created this colorful sky show originated from an increasingly active Sun. Surprisingly, since the approaching solar CME the day before had missed the Earth, it was not expected that this storm would create auroras. In the foreground, two happily surprised aurora hunters contemplate the amazing and rapidly changing sky. Regardless of forecasts, though, auroras were reported in the night skies of Earth not only in the far north, but as far south as New Mexico, USA. As captured in a wide-angle image above Saariselkä in northern Finnish Lapland, a bright aurora was visible with an unusually high degree of detail, range of colors, and breadth across the sky. The vivid yellow, green, red and purple auroral colors are caused by oxygen and nitrogen atoms high in Earth's atmosphere reacting to incoming electrons.

APOD: 2023 March 27 – Aurora Over Arctic Henge
Explanation: Reports of powerful solar flares started a seven-hour quest north to capture modern monuments against an aurora-filled sky. The peaks of iconic Arctic Henge in Raufarhöfn in northern Iceland were already aligned with the stars: some are lined up toward the exact north from one side and toward exact south from the other. The featured image, taken after sunset late last month, looks directly south, but since the composite image covers so much of the sky, the north star Polaris is actually visible at the very top of the frame. Also visible are familiar constellations including the Great Bear (Ursa Major) on the left, and the Hunter (Orion) on the lower right. The quest was successful. The sky lit up dramatically with bright and memorable auroras that shimmered with amazing colors including red, pink, yellow, and green -- sometimes several at once.

APOD: 2023 January 22 – In Green Company: Aurora over Norway
Explanation: Raise your arms if you see an aurora. With those instructions, two nights went by with, well, clouds -- mostly. On the third night of returning to same peaks, though, the sky not only cleared up but lit up with a spectacular auroral display. Arms went high in the air, patience and experience paid off, and the creative featured image was captured as a composite from three separate exposures. The setting is a summit of the Austnesfjorden fjord close to the town of Svolvear on the Lofoten islands in northern Norway. The time was early 2014. Although our Sun passed the solar minimum of its 11-year cycle only a few years ago, surface activity is picking up and already triggering more spectacular auroras here on Earth.

APOD: 2023 January 11 – Spiral Aurora over Iceland
Explanation: The scene may look like a fantasy, but it's really Iceland. The rock arch is named Gatklettur and located on the island's northwest coast. Some of the larger rocks in the foreground span a meter across. The fog over the rocks is really moving waves averaged over long exposures. The featured image is a composite of several foreground and background shots taken with the same camera and from the same location on the same night last November. The location was picked for its picturesque foreground, but the timing was planned for its colorful background: aurora. The spiral aurora, far behind the arch, was one of the brightest seen in the astrophotographer's life. The coiled pattern was fleeting, though, as auroral patterns waved and danced for hours during the cold night. Far in the background were the unchanging stars, with Earth's rotation causing them to appear to slowly circle the sky's northernmost point near Polaris.

APOD: 2022 April 4 - A Vortex Aurora over Iceland
Explanation: No, the car was not in danger of being vacuumed into space by the big sky vortex. For one reason, the vortex was really an aurora, and since auroras are created by particles striking the Earth from space, they do not create a vacuum. This rapidly developing auroral display was caused by a Coronal Mass Ejection from the Sun that passed by the Earth closely enough to cause a ripple in Earth's magnetosphere. The upper red parts of the aurora occur over 250 kilometers high with its red glow created by atmospheric atomic oxygen directly energized by incoming particles. The lower green parts of the aurora occur over 100 kilometers high with its green glow created by atmospheric atomic oxygen energized indirectly by collisions with first-energized molecular nitrogen. Below 100 kilometers, there is little atomic oxygen, which is why auroras end abruptly. The concentric cylinders depict a dramatic auroral corona as seen from the side. The featured image was created from a single 3-second exposure taken in mid-March over Lake Myvatn in Iceland.

APOD: 2022 March 22 - A Whale of an Aurora over Swedish Forest
Explanation: What's that in the sky? An aurora. A large coronal mass ejection occurred on our Sun earlier this month, throwing a cloud of fast-moving electrons, protons, and ions toward the Earth. Part of this cloud impacted our Earth's magnetosphere and, bolstered by a sudden gap, resulted in spectacular auroras being seen at some high northern latitudes. Featured here is a particularly photogenic auroral corona captured above a forest in Sweden from a scenic perch overlooking the city of Östersund. To some, this shimmering green glow of recombining atmospheric oxygen might appear like a large whale, but feel free to share what it looks like to you. The unusually quiet Sun of the past few years has now passed. As our Sun now approaches a solar maximum in its 11-year solar magnetic cycle, dramatic auroras like this are sure to continue.

APOD: 2022 February 20 - Aurora Over White Dome Geyser
Explanation: Sometimes both heaven and Earth erupt. Colorful auroras erupted unexpectedly a few years ago, with green aurora appearing near the horizon and brilliant bands of red aurora blooming high overhead. A bright Moon lit the foreground of this picturesque scene, while familiar stars could be seen far in the distance. With planning, the careful astrophotographer shot this image mosaic in the field of White Dome Geyser in Yellowstone National Park in the western USA. Sure enough, just after midnight, White Dome erupted -- spraying a stream of water and vapor many meters into the air. Geyser water is heated to steam by scalding magma several kilometers below, and rises through rock cracks to the surface. About half of all known geysers occur in Yellowstone National Park. Although the geomagnetic storm that caused the auroras subsided within a day, eruptions of White Dome Geyser continue about every 30 minutes.

APOD: 2022 February 12 - Aurora by Moonlight
Explanation: The ice was singing as light from a bright gibbous Moon cast shadows across this frozen lake, about 20 kilometers north of Stockholm, Sweden, planet Earth. In the alluring night skyscape captured on February 10, shimmering auroral curtains of light dance in the evening sky. On that northern night nature's performance included the auroral displays fostered by a minor geomagnetic storm. Stormy space weather was the result of a coronal mass ejection, erupting from a solar prominence days earlier and brushing our fair planet's magnetosphere.

APOD: 2022 February 8 - Aurora and Light Pillars over Norway
Explanation: Which half of this sky is your favorite? On the left, the night sky is lit up by particles expelled from the Sun that later collided with Earth's upper atmosphere — creating bright auroras. On the right, the night glows with ground lights reflected by millions of tiny ice crystals falling from the sky — creating light pillars. And in the center, the astrophotographer presents your choices. The light pillars are vertical columns because the fluttering ice-crystals are mostly flat to the ground, and their colors are those of the ground lights. The auroras cover the sky and ground in the green hue of glowing oxygen, while their transparency is clear because you can see stars right through them. Distant stars dot the background, including bright stars from the iconic constellation of Orion. The featured image was captured in a single exposure two months ago near Kautokeino, Norway.

APOD: 2021 October 30 - A Rorschach Aurora
Explanation: If you see this as a monster's face, don't panic. It's only pareidolia, often experienced as the tendency to see faces in patterns of light and shadow. In fact, the startling visual scene is actually a 180 degree panorama of Northern Lights, digitally mirrored like inkblots on a folded piece of paper. Frames used to construct it were captured on a September night from the middle of a waterfall-crossing suspension bridge in Jamtland, Sweden. With geomagnetic storms triggered by recent solar activity, auroral displays could be very active at planet Earth's high latitudes in the coming days. But if you see a monster's face in your own neighborhood tomorrow night, it might just be Halloween.

APOD: 2021 September 12 - A Spiral Aurora over Iceland
Explanation: What's happened to the sky? Aurora! Captured in 2015, this aurora was noted by Icelanders for its great brightness and quick development. The aurora resulted from a solar storm, with high energy particles bursting out from the Sun and through a crack in Earth's protective magnetosphere a few days later. Although a spiral pattern can be discerned, creative humans might imagine the complex glow as an atmospheric apparition of any number of common icons. In the foreground of the featured image is the Ölfusá River while the lights illuminate a bridge in Selfoss City. Just beyond the low clouds is a nearly full Moon. The liveliness of the Sun -- and likely the resulting auroras on Earth -- is slowly increasing as the Sun emerges from a Solar minimum, a historically quiet period in its 11-year cycle.

APOD: 2021 May 30 - Aurora over Clouds
Explanation: Auroras usually occur high above the clouds. The auroral glow is created when fast-moving particles ejected from the Sun impact the Earth's magnetosphere, from which charged particles spiral along the Earth's magnetic field to strike atoms and molecules high in the Earth's atmosphere. An oxygen atom, for example, will glow in the green light commonly emitted by an aurora after being energized by such a collision. The lowest part of an aurora will typically occur about 100 kilometers up, while most clouds exist only below about 10 kilometers. The relative heights of clouds and auroras are shown clearly in the featured picture in 2015 from Dyrholaey, Iceland. There, a determined astrophotographer withstood high winds and initially overcast skies in an attempt to capture aurora over a picturesque lighthouse, only to take, by chance, the featured picture including elongated lenticular clouds, along the way.

APOD: 2021 March 24 - Aurorae and Lightning on Jupiter
Explanation: Why does so much of Jupiter's lightning occur near its poles? Similar to Earth, Jupiter experiences both aurorae and lightning. Different from Earth, though, Jupiter's lightning usually occurs near its poles -- while much of Earth's lightning occurs near its equator. To help understand the difference, NASA's Juno spacecraft, currently orbiting Jupiter, has observed numerous aurora and lightning events. The featured image, taken by Juno's Stellar Reference Unit camera on 2018 May 24, shows Jupiter's northern auroral oval and several bright dots and streaks. An eye-catching event is shown in the right inset image -- which is a flash of Jupiter's lightning -- one of the closest images of aurora and lightning ever. On Earth (which is much nearer to the Sun than Jupiter), sunlight is bright enough to create, by itself, much stronger atmospheric heating at the equator than the poles, driving turbulence, storms, and lightning. On Jupiter, in contrast, atmospheric heating comes mostly from its interior (as a remnant from its formation), leading to the hypothesis that more intense equatorial sunlight reduces temperature differences between upper atmospheric levels, hence reducing equatorial lightning-creating storms.

APOD: 2021 March 14 - A Flag Shaped Aurora over Sweden
Explanation: It appeared, momentarily, like a 50-km tall banded flag. In mid-March of 2015, an energetic Coronal Mass Ejection directed toward a clear magnetic channel to Earth led to one of the more intense geomagnetic storms of recent years. A visual result was wide spread auroras being seen over many countries near Earth's magnetic poles. Captured over Kiruna, Sweden, the image features an unusually straight auroral curtain with the green color emitted low in the Earth's atmosphere, and red many kilometers higher up. It is unclear where the rare purple aurora originates, but it might involve an unusual blue aurora at an even lower altitude than the green, seen superposed with a much higher red. Now past Solar Minimum, colorful nights of auroras over Earth are likely to increase.

APOD: 2021 February 28 - The Aurora Tree
Explanation: Yes, but can your tree do this? Pictured is a visual coincidence between the dark branches of a nearby tree and bright glow of a distant aurora. The beauty of the aurora -- combined with how it seemed to mimic a tree right nearby -- mesmerized the photographer to such a degree that he momentarily forgot to take pictures. When viewed at the right angle, it seemed that this tree had aurora for leaves. Fortunately, before the aurora morphed into a different overall shape, he came to his senses and capture the awe-inspiring momentary coincidence. Typically triggered by solar explosions, aurora are caused by high energy electrons impacting the Earth's atmosphere around 150 kilometers up. The unusual Earth-sky collaboration was witnessed in March of 2017 in Iceland.

APOD: 2021 January 14 - Aurora Slathers Up the Sky
Explanation: Like salsa verde on your favorite burrito, a green aurora slathers up the sky in this 2017 June 25 snapshot from the International Space Station. About 400 kilometers (250 miles) above Earth, the orbiting station is itself within the upper realm of the auroral displays. Aurorae have the signature colors of excited molecules and atoms at the low densities found at extreme altitudes. Emission from atomic oxygen dominates this view. The tantalizing glow is green at lower altitudes, but rarer reddish bands extend above the space station's horizon. The orbital scene was captured while passing over a point south and east of Australia, with stars above the horizon at the right belonging to the constellation Canis Major, Orion's big dog. Sirius, alpha star of Canis Major, is the brightest star near the Earth's limb.

APOD: 2021 January 3 - A Phoenix Aurora over Iceland
Explanation: All of the other aurora watchers had gone home. By 3:30 am in Iceland, on a quiet September night, much of that night's auroras had died down. Suddenly, unexpectedly, a new burst of particles streamed down from space, lighting up the Earth's atmosphere once again. This time, surprisingly, pareidoliacally, the night lit up with an amazing shape reminiscent of a giant phoenix. With camera equipment at the ready, two quick sky images were taken, followed immediately by a third of the land. The mountain in the background is Helgafell, while the small foreground river is called Kaldá, both located about 30 kilometers north of Iceland's capital Reykjavík. Seasoned skywatchers will note that just above the mountain, toward the left, is the constellation of Orion, while the Pleiades star cluster is also visible just above the frame center. The 2016 aurora, which lasted only a minute and was soon gone forever -- would possibly be dismissed as an fanciful fable -- were it not captured in the featured, digitally-composed, image mosaic.

APOD: 2020 November 9 - In Green Company: Aurora over Norway
Explanation: Raise your arms if you see an aurora. With those instructions, two nights went by with, well, clouds -- mostly. On the third night of returning to same peaks, though, the sky not only cleared up but lit up with a spectacular auroral display. Arms went high in the air, patience and experience paid off, and the creative featured image was captured as a composite from three separate exposures. The setting is a summit of the Austnesfjorden fjord close to the town of Svolvear on the Lofoten islands in northern Norway. The time was early 2014. Although our Sun has just passed the solar minimum of its 11-year cycle, surface activity should pick up over the next few years with the promise of triggering more spectacular auroras on Earth.

APOD: 2020 May 31 - Aurora over Sweden
Explanation: It was bright and green and stretched across the sky. This striking aurora display was captured in 2016 just outside of Östersund, Sweden. Six photographic fields were merged to create the featured panorama spanning almost 180 degrees. Particularly striking aspects of this aurora include its sweeping arc-like shape and its stark definition. Lake Storsjön is seen in the foreground, while several familiar constellations and the star Polaris are visible through the aurora, far in the background. Coincidently, the aurora appears to avoid the Moon visible on the lower left. The aurora appeared a day after a large hole opened in the Sun's corona allowing particularly energetic particles to flow out into the Solar System. The green color of the aurora is caused by oxygen atoms recombining with ambient electrons high in the Earth's atmosphere.

APOD: 2020 January 4 - Aurora Slathers Up the Sky
Explanation: Like salsa verde on your favorite burrito, a green aurora slathers up the sky in this 2017 June 25 snapshot from the International Space Station. About 400 kilometers (250 miles) above Earth, the orbiting station is itself within the upper realm of the auroral displays. Aurorae have the signature colors of excited molecules and atoms at the low densities found at extreme altitudes. Emission from atomic oxygen dominates this view. The tantalizing glow is green at lower altitudes, but rarer reddish bands extend above the space station's horizon. The orbital scene was captured while passing over a point south and east of Australia, with stars above the horizon at the right belonging to the constellation Canis Major, Orion's big dog. Sirius, alpha star of Canis Major, is the brightest star near the Earth's limb.

APOD: 2019 October 27 - Ghost Aurora over Canada
Explanation: What does this aurora look like to you? While braving the cold to watch the skies above northern Canada early one morning in 2013, a most unusual aurora appeared. The aurora definitely appeared to be shaped like something , but what? Two ghostly possibilities recorded by the astrophotographer were "witch" and "goddess of dawn", but please feel free to suggest your own Halloween-enhanced impressions. Regardless of fantastical pareidolic interpretations, the pictured aurora had a typical green color and was surely caused by the scientifically commonplace action of high energy particles from space interacting with oxygen in Earth's upper atmosphere. In the image foreground, at the bottom, is a frozen Alexandra Falls, while evergreen trees cross the middle.

APOD: 2019 July 14 - Eagle Aurora over Norway
Explanation: What's that in the sky? An aurora. A large coronal mass ejection occurred on our Sun five days before this 2012 image was taken, throwing a cloud of fast moving electrons, protons, and ions toward the Earth. Although most of this cloud passed above the Earth, some of it impacted our Earth's magnetosphere and resulted in spectacular auroras being seen at high northern latitudes. Featured here is a particularly photogenic auroral corona captured above Grotfjord, Norway. To some, this shimmering green glow of recombining atmospheric oxygen might appear as a large eagle, but feel free to share what it looks like to you. Although the Sun is near Solar Minimum, streams of the solar wind continue to impact the Earth and create impressive auroras visible even last week.

APOD: 2019 April 21 - Spiral Aurora over Icelandic Divide
Explanation: Admire the beauty but fear the beast. The beauty is the aurora overhead, here taking the form of great green spiral, seen between picturesque clouds with the bright Moon to the side and stars in the background. The beast is the wave of charged particles that creates the aurora but might, one day, impair civilization. In 1859, following notable auroras seen all across the globe, a pulse of charged particles from a coronal mass ejection (CME) associated with a solar flare impacted Earth's magnetosphere so forcefully that they created the Carrington Event. A relatively direct path between the Sun and the Earth might have been cleared by a preceding CME. What is sure is that the Carrington Event compressed the Earth's magnetic field so violently that currents were created in telegraph wires so great that many wires sparked and gave telegraph operators shocks. Were a Carrington-class event to impact the Earth today, speculation holds that damage might occur to global power grids and electronics on a scale never yet experienced. The featured aurora was imaged in 2016 over Thingvallavatn Lake in Iceland, a lake that partly fills a fault that divides Earth's large Eurasian and North American tectonic plates.

APOD: 2019 February 18 - Dragon Aurora over Iceland
Explanation: Have you ever seen a dragon in the sky? Although real flying dragons don't exist, a huge dragon-shaped aurora developed in the sky over Iceland earlier this month. The aurora was caused by a hole in the Sun's corona that expelled charged particles into a solar wind that followed a changing interplanetary magnetic field to Earth's magnetosphere. As some of those particles then struck Earth's atmosphere, they excited atoms which subsequently emitted light: aurora. This iconic display was so enthralling that the photographer's mother ran out to see it and was captured in the foreground. No sunspots have appeared on the Sun so far in February, making the multiple days of picturesque auroral activity this month somewhat surprising.

APOD: 2018 December 9 - Aurora Shimmer, Meteor Flash
Explanation: Some night skies are serene and passive -- others shimmer and flash. The later, in the form of auroras and meteors, haunted skies over the island of Kvaløya, near Tromsø Norway on 2009 December 13. This 30 second long exposure records a shimmering auroral glow gently lighting the wintery coastal scene. A study in contrasts, the image also captures the sudden flash of a fireball meteor from the excellent Geminid meteor shower of 2009. Streaking past familiar stars in the handle of the Big Dipper, the trail points back toward the constellation Gemini, off the top of the view. Both auroras and meteors occur in Earth's upper atmosphere at altitudes of 100 kilometers or so, but aurora caused by energetic charged particles from the magnetosphere, while meteors are trails of cosmic dust. Nine years after this photograph was taken, toward the end of this week, the yearly 2018 Geminids meteor shower will peak again, although this time their flashes will compete with the din of a half-lit first-quarter moon during the first half of the night.

APOD: 2018 November 18 - Creature Aurora Over Norway
Explanation: It was Halloween and the sky looked like a creature. Exactly which creature, the astrophotographer was unsure but (possibly you can suggest one). Exactly what caused this eerie apparition in 2013 was sure: one of the best auroral displays in recent years. This spectacular aurora had an unusually high degree of detail. Pictured here, the vivid green and purple auroral colors are caused by high atmospheric oxygen and nitrogen reacting to a burst of incoming electrons. Birch trees in Tromsø, Norway formed an also eerie foreground. Recently, new photogenic auroras have accompanied new geomagnetic storms.

APOD: 2018 October 6 - Aurora: The Frog's View
Explanation: What does an aurora look like to a frog? "Awesome!" is the likely answer, suggested by this imaginative snapshot taken on October 3rd from Kiruna, Sweden. Frequented by apparitions of the northern lights, Kiruna is located in Lapland north of the Arctic Circle, and often under the auroral oval surrounding planet Earth's geomagnetic north pole. To create a tantalizing view from a frog's perspective the photographer turned on the flashlight on her phone and placed it on the ground facing down, resting her camera's lens on top. The "diamonds" in the foreground are icy pebbles right in front of the lens, lit up by the flashlight. Reflecting the shimmering northern lights, the "lake" is a frozen puddle on the ground. Of course, in the distance is the Bengt Hultqvist Observatory.

APOD: 2018 September 22 - Window Seat over Hudson Bay
Explanation: On the August 18 night flight from San Francisco to Zurich, a window seat offered this tantalizing view when curtains of light draped a colorful glow across the sky over Hudson Bay. Constructed by digitally stacking six short exposures made with a hand held camera, the scene records the shimmering aurora borealis or northern lights just as the approaching high altitude sunrise illuminated the northeastern horizon. It also caught the flash of a Perseid meteor streaking beneath the handle stars of the Big Dipper of the north. A few days past the meteor shower's peak, its trail still points across the sky toward Perseus. Beautiful aurorae and shower meteors both occur in Earth's upper atmosphere at altitudes of 100 kilometers or so, far above commercial airline flights. The aurora are caused by energetic charged particles from the magnetosphere, while meteors are trails of comet dust.

APOD: 2018 September 3 - Aurora around Saturns North Pole
Explanation: Are Saturn's auroras like Earth's? To help answer this question, the Hubble Space Telescope and the Cassini spacecraft monitored Saturn's North Pole simultaneously during Cassini's final orbits around the gas giant in September 2017. During this time, Saturn's tilt caused its North Pole to be clearly visible from Earth. The featured image is a composite of ultraviolet images of aurora and optical images of Saturn's clouds and rings, all taken recently by Hubble. Like on Earth, Saturn's northern auroras can make total or partial rings around the pole. Unlike on Earth, however, Saturn's auroras are frequently spirals -- and more likely to peak in brightness just before midnight and dawn. In contrast to Jupiter's auroras, Saturn's auroras appear better related to connecting Saturn's internal magnetic field to the nearby, variable, solar wind. Saturn's southern auroras were similarly imaged back in 2004 when the planet's South Pole was clearly visible to Earth.

APOD: 2018 May 29 - Aurora and Manicouagan Crater from the Space Station
Explanation: How many of these can you find in today's featured photograph: an aurora, airglow, one of the oldest impact craters on the Earth, snow and ice, stars, city lights, and part of the International Space Station? Most of these can be identified by their distinctive colors. The aurora here appears green at the bottom, red at the top, and is visible across the left of image. Airglow appears orange and can be seen hovering over the curve of the Earth. The circular Manicouagan Crater in Canada, about 100 kilometers across and 200 million years old, is visible toward the lower right and is covered in white snow and ice. Stars, light in color, dot the dark background of space. City lights appear a bright yellow and dot the landscape. Finally, across the top, part of the International Space Station (ISS) appears mostly tan. The featured image was taken from the ISS in 2012.

APOD: 2018 May 1 - The Aurora and the Sunrise
Explanation: On the International Space Station (ISS), you can only admire an aurora until the sun rises. Then the background Earth becomes too bright. Unfortunately, after sunset, the rapid orbit of the ISS around the Earth means that sunrise is usually less than 47 minutes away. In the featured image, a green aurora is visible below the ISS -- and on the horizon to the upper right, while sunrise approaches ominously from the upper left. Watching an aurora from space can be mesmerizing as its changing shape has been compared to a giant green amoeba. Auroras are composed of energetic electrons and protons from the Sun that impact the Earth's magnetic field and then spiral down toward the Earth so fast that they cause atmospheric atoms and molecules to glow. The ISS orbits at nearly the same height as auroras, many times flying right through an aurora's thin upper layers, an event that neither harms astronauts nor changes the shape of the aurora.

APOD: 2018 April 10 - Dragon Aurora over Norway
Explanation: What's that in the sky? An aurora. A large coronal hole opened last month, a few days before this image was taken, throwing a cloud of fast moving electrons, protons, and ions toward the Earth. Some of this cloud impacted our Earth's magnetosphere and resulted in spectacular auroras being seen at high northern latitudes. Featured here is a particularly photogenic auroral curtain captured above Tromsø Norway. To the astrophotographer, this shimmering green glow of recombining atmospheric oxygen appeared as a large dragon, but feel free to share what it looks like to you. Although now past Solar Maximum, our Sun continues to show occasional activity creating impressive auroras on Earth visible even last week.

APOD: 2017 December 10 - In Green Company: Aurora over Norway
Explanation: Raise your arms if you see an aurora. With those instructions, two nights went by with, well, clouds -- mostly. On the third night of returning to same peaks, though, the sky not only cleared up but lit up with a spectacular auroral display. Arms went high in the air, patience and experience paid off, and the creative featured image was captured as a composite from three separate exposures. The setting is a summit of the Austnesfjorden fjord close to the town of Svolvear on the Lofoten islands in northern Norway. The time was early 2014. Although our Sun is nearing Solar Minimum and hence showing relatively little surface activity, holes in the upper corona have provided some nice auroral displays over the last few months.

APOD: 2017 October 14 - All Sky Steve
Explanation: Familiar green and red tinted auroral emission floods the sky along the northern (top) horizon in this fish-eye panorama projection from September 27. On the mild, clear evening the Milky Way tracks through the zenith of a southern Alberta sky and ends where the six-day-old Moon sets in the southwest. The odd, isolated, pink and whitish arc across the south has come to be known as Steve. The name was given to the phenomenon by the Alberta Aurora Chasers Facebook group who had recorded appearances of the aurora-like feature. Sometimes mistakenly identified as a proton aurora or proton arc, the mysterious Steve arcs seem associated with aurorae but appear closer to the equator than the auroral curtains. Widely documented by citizen scientists and recently directly explored by a Swarm mission satellite, Steve arcs have been measured as thermal emission from flowing gas rather than emission excited by energetic electrons. Even though a reverse-engineered acronym that fits the originally friendly name is Sudden Thermal Emission from Velocity Enhancement, his origin is still mysterious.

APOD: 2017 October 6 - Global Aurora at Mars
Explanation: A strong solar event last month triggered intense global aurora at Mars. Before (left) and during (right) the solar storm, these projections show the sudden increase in ultraviolet emission from martian aurora, more than 25 times brighter than auroral emission previously detected by the orbiting MAVEN spacecraft. With a sunlit crescent toward the right, data from MAVEN's ultraviolet imaging spectrograph is shown in purple hues on the night side of Mars globes simulated to match the observation dates and times. On Mars, solar storms can result in planet-wide aurora because, unlike Earth, the Red Planet isn't protected by a strong global magnetic field that can funnel energetic charged particles toward the poles. For all those on the planet's surface during the solar storm, dangerous radiation levels were double any previously measured by the Curiosity rover. MAVEN is studying whether Mars lost its atmosphere due to its lack of a global magnetic field.

APOD: 2017 July 29 - Aurora Slathers up the Sky
Explanation: Like salsa verde on your favorite burrito, a green aurora slathers up the sky in this June 25 snapshot from the International Space Station. About 400 kilometers (250 miles) above Earth, the orbiting station is itself within the upper realm of the auroral displays. Aurorae have the signature colors of excited molecules and atoms at the low densities found at extreme altitudes. Emission from atomic oxygen dominates this view. The tantalizing glow is green at lower altitudes, but rarer reddish bands extend above the space station's horizon. The orbital scene was captured while passing over a point south and east of Australia, with stars above the horizon at the right belonging to the constellation Canis Major, Orion's big dog. Sirius, alpha star of Canis Major, is the brightest star near the Earth's limb.

APOD: 2017 May 13 - Planet Aurora
Explanation: What bizarre alien planet is this? It's planet Earth of course, seen from the International Space Station through the shimmering glow of aurorae. About 400 kilometers (250 miles) above Earth, the orbiting station is itself within the upper realm of the auroral displays. Aurorae have the signature colors of excited molecules and atoms at the low densities found at extreme altitudes. Emission from atomic oxygen dominates this view. The eerie glow is green at lower altitudes, but a rarer reddish band extends above the space station's horizon. Also visible from the planet's surface, this auroral display began during a geomagnetic storm. The storm was triggered after a coronal mass ejection impacted Earth's magnetosphere in June of 2015.

APOD: 2017 March 20 - The Aurora Tree
Explanation: Yes, but can your tree do this? Pictured is a visual coincidence between the dark branches of a nearby tree and bright glow of a distant aurora. The beauty of the aurora -- combined with how it seemed to mimic a tree right nearby -- mesmerized the photographer to such a degree that he momentarily forgot to take pictures. When viewed at the right angle, it seemed that this tree had aurora for leaves! Fortunately, before the aurora morphed into a different overall shape, he came to his senses and capture the awe-inspiring momentary coincidence. Typically triggered by solar explosions, aurora are caused by high energy electrons impacting the Earth's atmosphere around 150 kilometers up. The unusual Earth-sky collaboration was witnessed earlier this month in Iceland.

APOD: 2017 March 6 - Colorful Aurora over Iceland
Explanation: You don't always see a scene this beautiful when you hike to an ancient volcano -- you have to be lucky. When the astrophotographer realized that auroras were visible two-weeks ago, he made a night-time run for the top of the caldera to see if he could capture them also reflected in the central lake. When he arrived, he found that ... the northern lights were even brighter and more impressive than before! And his image of them is the featured 13-frame panoramic mosaic. The crater lake in the center is called Kerid (Icelandic: Kerið) and is about 3,000 years old. The aurora overhead shows impressive colors and banding, with the red colors occurring higher in the Earth's atmosphere than the green. The background sky is filled with icons of the northern night including Polaris, the Pleiades star cluster, and the stars that compose the handle of the Big Dipper.

APOD: 2017 January 29 - Red Aurora Over Australia
Explanation: Why would the sky glow red? Aurora. A solar storm in 2012, emanating mostly from active sunspot region 1402, showered particles on the Earth that excited oxygen atoms high in the Earth's atmosphere. As the excited element's electrons fell back to their ground state, they emitted a red glow. Were oxygen atoms lower in Earth's atmosphere excited, the glow would be predominantly green. Pictured here, this high red aurora is visible just above the horizon last week near Flinders, Victoria, Australia. The sky that night, however, also glowed with more familiar but more distant objects, including the central disk of our Milky Way Galaxy on the left, and the neighboring Large and Small Magellanic Cloud galaxies on the right. A time-lapse video highlighting auroras visible that night puts the picturesque scene in context. Why the sky did not also glow green remains unknown.

APOD: 2017 January 1 - A Full Sky Aurora Over Norway
Explanation: Higher than the highest building, higher than the highest mountain, higher than the highest airplane, lies the realm of the aurora. Auroras rarely reach below 60 kilometers, and can range up to 1000 kilometers. Aurora light results from energetic electrons and protons striking molecules in the Earth's atmosphere. Frequently, when viewed from space, a complete aurora will appear as a circle around one of the Earth's magnetic poles. The featured wide-angle image, horizontally compressed, captured an unexpected auroral display that stretched across the sky five years ago over eastern Norway.

APOD: 2016 December 6 - Aurora over Jupiter's South Pole from Juno
Explanation: Why is there a glowing oval over Jupiter's South Pole? Aurora. Near the closest part of its first pass near Jupiter in August, NASA's robotic spacecraft Juno captured this dramatic infrared image of a bright auroral ring. Auroras are caused by high energy particles from the Sun interacting with a planet's magnetic field, and ovals around magnetic poles are common. Data from Juno are giving preliminary indications that Jupiter's magnetic field and aurorae are unexpectedly powerful and complex. Unfortunately, a computer glitch caused Juno to go into safe mode during its October pass near the Jovian giant in October. That glitch has now been resolved, making Juno ready for its next pass over Jupiter's cloud tops this coming Sunday.

APOD: 2016 October 31 - Ghost Aurora over Canada
Explanation: What does this aurora look like to you? While braving the cold to watch the skies above northern Canada early one morning in 2013, a most unusual aurora appeared. The aurora definitely appeared to be shaped like something , but what? Two ghostly possibilities recorded by the astrophotographer were "witch" and "goddess of dawn", but please feel free to suggest your own Halloween-enhanced impressions. Regardless of fantastical pareidolic interpretations, the pictured aurora had a typical green color and was surely caused by the scientifically commonplace action of high energy particles from space interacting with oxygen in Earth's upper atmosphere. In the image foreground, at the bottom, is a frozen Alexandra Falls, while evergreen trees cross the middle.

APOD: 2016 October 23 - Eagle Aurora over Norway
Explanation: What's that in the sky? An aurora. A large coronal mass ejection occurred on our Sun five days before this 2012 image was taken, throwing a cloud of fast moving electrons, protons, and ions toward the Earth. Although most of this cloud passed above the Earth, some of it impacted our Earth's magnetosphere and resulted in spectacular auroras being seen at high northern latitudes. Featured here is a particularly photogenic auroral corona captured above Grotfjord, Norway. To some, this shimmering green glow of recombining atmospheric oxygen might appear as a large eagle, but feel free to share what it looks like to you. Although now past Solar Maximum, our Sun continues to show occasional activity creating impressive auroras on Earth visible only last week.

APOD: 2016 October 2 - Aurora Over White Dome Geyser
Explanation: Sometimes both heaven and Earth erupt. Colorful aurorae erupted unexpectedly a few years ago, with green aurora appearing near the horizon and brilliant bands of red aurora blooming high overhead. A bright Moon lit the foreground of this picturesque scene, while familiar stars could be seen far in the distance. With planning, the careful astrophotographer shot this image mosaic in the field of White Dome Geyser in Yellowstone National Park in the western USA. Sure enough, just after midnight, White Dome erupted -- spraying a stream of water and vapor many meters into the air. Geyser water is heated to steam by scalding magma several kilometers below, and rises through rock cracks to the surface. About half of all known geysers occur in Yellowstone National Park. Although the geomagnetic storm that created these aurorae has since subsided, eruptions of White Dome Geyser continue about every 30 minutes.

APOD: 2016 August 30 - Aurora over Icelandic Fault
Explanation: Admire the beauty but fear the beast. The beauty is the aurora overhead, here taking the form of great green spiral, seen between picturesque clouds with the bright Moon to the side and stars in the background. The beast is the wave of charged particles that creates the aurora but might, one day, impair civilization. Exactly this week in 1859, following notable auroras seen all across the globe, a pulse of charged particles from a coronal mass ejection (CME) associated with a solar flare impacted Earth's magnetosphere so forcefully that they created the Carrington Event. A relatively direct path between the Sun and the Earth might have been cleared by a preceding CME. What is sure is that the Carrington Event compressed the Earth's magnetic field so violently that currents were created in telegraph wires so great that many wires sparked and gave telegraph operators shocks. Were a Carrington-class event to impact the Earth today, speculation holds that damage might occur to global power grids and electronics on a scale never yet experienced. The featured aurora was imaged last week over Thingvallavatn Lake in Iceland, a lake that partly fills a fault that divides Earth's large Eurasian and North American tectonic plates.

APOD: 2016 August 11 - Perseid, Aurora, and Noctilucent Clouds
Explanation: Night skies over northern Sweden can hold some tantalizing sights in August. Gazing toward the Big Dipper, this beautiful skyscape captures three of them in a single frame taken last August 12/13. Though receding from northern skies for the season, night shining or noctilucent clouds are hanging just above the horizon. Extreme altitude icy condensations on meteoric dust, they were caught here just below an early apparition of a lovely green auroral band, also shining near the edge of space. The flash of a Perseid meteor near the peak of the annual shower punctuates the scene. In fact, this year's Perseid shower will peak in the coming days, offering a continuing chance for a night sky photographer's hat trick.

APOD: 2016 May 3 - Aurora over Sweden
Explanation: It was bright and green and stretched across the sky. This striking aurora display was captured last month just outside of Östersund, Sweden. Six photographic fields were merged to create the featured panorama spanning almost 180 degrees. Particularly striking aspects of this aurora include its sweeping arc-like shape and its stark definition. Lake Storsjön is seen in the foreground, while several familiar constellations and the star Polaris are visible through the aurora, far in the background. Coincidently, the aurora appears to avoid the Moon visible on the lower left. The aurora appeared a day after a large hole opened in the Sun's corona allowing particularly energetic particles to flow out into the Solar System. The green color of the aurora is caused by oxygen atoms recombining with ambient electrons high in the Earth's atmosphere.

APOD: 2016 April 4 - Lucid Dreaming
Explanation: Is this the real world? Or is it just fantasy? The truth started with a dream -- a dream that the spectacular Seljarlandsfoss waterfall in southern Iceland could be photographed with a backdrop of an aurora-filled sky. Soon after a promising space weather report, the visionary astrophotographer and his partner sprang into action. After arriving, capturing an image of the background sky, complete with a cool green aurora, turned out to be the easy part. The hard part was capturing the waterfall itself, for one reason because mist kept fogging the lens! Easy come, easy go -- it took about 100 times where someone had to go back to the camera -- on a cold night and over slippery rocks -- to see how the last exposure turned out, wipe the lens, and reset the camera for the next try. Later, the best images of land and sky were digitally combined. Visible in the sky, even well behind the aurora, are numerous stars of the northern sky. The resulting title -- given by the astrophotographer -- was influenced by a dream-like quality of the resulting image, possibly combined with the knowledge that some things really mattered in this effort to make a dream come true.

APOD: 2016 March 16 - A Phoenix Aurora over Iceland
Explanation: All of the other aurora watchers had gone home. By 3:30 am in Iceland, on a quiet night last September, much of that night's auroras had died down. Suddenly though, a new burst of particles streamed down from space, lighting up the Earth's atmosphere once again. This time, unexpectedly, pareidoliacally, they created an amazing shape reminiscent of a giant phoenix. With camera equipment at the ready, two quick sky images were taken, followed immediately by a third of the land. The mountain in the background is Helgafell, while the small foreground river is called Kaldá, both located about 30 kilometers north of Iceland's capital Reykjavik. Seasoned skywatchers will note that just above the mountain, toward the left, is the constellation of Orion, while the Pleiades star cluster is also visible just above the frame center. The new aurora lasted only a minute and would be gone forever -- possibly dismissed as an embellished aberration -- were it not captured in the featured, digitally-composed, image mosaic.

APOD: 2015 December 8 - Icelandic Legends and Aurora
Explanation: Legends collide in this dramatic vista of land, sea, and sky. The land is Iceland, specifically Vík í Mýrdal, a southern village known for its beautiful black sand beaches. The sea, the Atlantic Ocean, surrounds Reynisdrangar, a sea stack of eroded basaltic rock pillars that Icelandic folklore tells are the petrified remains of trolls once attempting to drag a three-masted ship onto land. Watching from overhead and shining bright on the upper right is the god of the sky, according to Greek mythology: the planet Jupiter. Also visible in the sky are several other Greek legends encapsulated as constellations, including a lion (Leo), a big bear (Ursa Major), and a water snake (Hydra). One might guess that all of this commotion caused the spectacular aurora pictured -- but really it was just explosions from the Sun.

APOD: 2015 November 24 - Aurora over Clouds
Explanation: Auroras usually occur high above the clouds. The auroral glow is created when fast-moving particles ejected from the Sun impact the Earth's magnetosphere, from which charged particles spiral along the Earth's magnetic field to strike atoms and molecules high in the Earth's atmosphere. An oxygen atom, for example, will glow in the green light commonly emitted by an aurora after being energized by such a collision. The lowest part of an aurora will typically occur at 100 kilometers up, while most clouds usually exist only below about 10 kilometers. The relative heights of clouds and auroras are shown clearly in the featured picture from Dyrholaey, Iceland. There, a determined astrophotographer withstood high winds and initially overcast skies in an attempt to capture aurora over a picturesque lighthouse, only to take, by chance, the featured picture along the way.

APOD: 2015 September 15 - A Spiral Aurora over Iceland
Explanation: What's happened to the sky? Aurora! Captured late last month, this aurora was noted by Icelanders for its great brightness and quick development. The aurora resulted from a solar storm, with high energy particles bursting out from the Sun and through a crack in Earth's protective magnetosphere a few days later. Although a spiral pattern can be discerned, creative humans might imagine the complex glow as an atmospheric apparition of any number of common icons. In the foreground of the featured image is the Ölfusá River, while the lights illuminate a bridge in Selfoss City. Just beyond the low clouds is a nearly full Moon. The liveliness of the Sun -- and the resulting auroras on Earth -- is slowly diminishing as the Sun emerges from a Solar maximum of surface activity and evolves towards a historically more quite period in its 11-year cycle. In fact, solar astronomers are waiting to see if the coming Solar minimum will be as unusually quiet as the last one, where sometimes months would go by with no discernible sunspots or other active solar phenomena.

APOD: 2015 August 3 - A Proton Arc Over Lake Superior
Explanation: The setting had been picked out -- all that was needed was an aurora. And late last August, forecasts predicted that an otherwise beautiful night sky would be lit up with auroral green. Jumping into his truck, the astrophotographer approached his secret site -- but only after a five hour drive across the rural Upper Peninsula of Michigan. What he didn't know was that his luck was just beginning. While setting up for the image, a proton arc -- a rare type of aurora -- appeared. The red arc lasted only about 15 minutes, but that was long enough to capture in a 30-second exposure. As the name indicates, proton arcs are caused not by electrons but by more massive protons that bombard the Earth's atmosphere following an energetic event on the Sun. In the featured image, the yellow lights on the horizon are the city lights of Marquette, Michigan, USA. The blue and yellow rocks in the Lake Superior foreground are lit by a LED flashlight. Also captured, to the left of the red proton arc, was the band of our Milky Way Galaxy.

APOD: 2015 July 27 - Milky Way and Aurora over Antarctica
Explanation: It has been one of the better skies of this long night. In parts of Antarctica, not only is it winter, but the Sun can spend weeks below the horizon. At China's Zhongshan Station, people sometimes venture out into the cold to photograph a spectacular night sky. The featured image from one such outing was taken in mid-July, just before the end of this polar night. Pointing up, the wide angle lens captured not only the ground at the bottom, but at the top as well. In the foreground is a colleague also taking pictures. In the distance, a spherical satellite receiver and several windmills are visible. Numerous stars dot the night sky, including Sirius and Canopus. Far in the background, stretching overhead from horizon to horizon, is the central band of our Milky Way Galaxy. Even further in the distance, visible as extended smudges near the top, are the Large and Small Magellanic Clouds, satellite galaxies near our huge Milky Way Galaxy.

APOD: 2015 July 4 - Aurora Australis
Explanation: Not fireworks, these intense shimmering lights still danced across Earth's night skies late last month, seen here above the planet's geographic south pole. The stunning auroral displays were triggered as a coronal mass ejection blasted from the Sun days earlier impacted the magnetosphere, beginning a widespread geomagnetic storm. The six fisheye panels were recorded with digital camera and battery in a heated box to guard against -90 degree F ambient temperatures of the long winter night. Around the horizon are south pole astronomical observatories, while beyond the Aurora Australis stretch the stars of the southern Milky Way.

APOD: 2015 June 26 - Planet Aurora
Explanation: What bizarre alien planet is this ? It's planet Earth of course, seen through the shimmering glow of aurorae from the International Space Station. About 400 kilometers (250 miles) above, the orbiting station is itself within the upper realm of the auroral displays, also watched from the planet's surface on June 23rd. Aurorae have the signature colors of excited molecules and atoms at the low densities found at extreme altitudes. The eerie greenish glow of molecular oxygen dominates this view. But higher, just above the space station's horizon, is a rarer red band of aurora from atomic oxygen. The ongoing geomagnetic storm began after a coronal mass ejection's recent impact on Earth's magnetosphere.

APOD: 2015 June 1 - Pulsating Aurora over Iceland
Explanation: Why do some auroras pulsate? No one is sure. Although this unusual behavior has been known for a long time, the cause remains an active topic of research. Featured here is a dramatic video that captured some impressive pulsating auroras in mid-March over Svínafellsjökull Glacier in Iceland. The 48-second video shown is not time-lapse. The real-time pulsations are exemplified by sequences where the astrophotographer is visible moving about in the foreground. A close inspection of the enigmatic flickering sky colors reveals that some structures appear to repeat, while others do not. The quick rapidity of the pulsations seen here is somewhat unusual -- more common are aurora with pulsations that last several seconds. Recent research shows that pulsations are more common in electron-generated aurora, rather than proton aurora, and that the Earth's local magnetic field may fluctuate in unison.

APOD: 2015 May 4 - An Unexpected Aurora over Norway
Explanation: Sometimes the sky lights up unexpectedly. A trip to northern Norway to photograph auroras was not going as well as hoped. It was now past midnight in Steinsvik, Troms, in northern Norway, and the date was 2014 February 8. Despite recent activity on the Sun, the skies were disappointing. Therefore, the astrophotographer began packing up to go. His brother began searching for a missing lens cap. When the sky suddenly exploded with spectacular aurora. Reacting quickly, a sequence detailing dramatic green curtains was captured, with the bright Moon near the image center, and the lens-cap seeking brother on the far right. The auroral flare lasted only a few minutes, but the memory of this event, the photographer speculates, will last much longer.

APOD: 2015 March 30 - A Flag Shaped Aurora over Sweden
Explanation: It appeared, momentarily, like a 50-km tall banded flag. In mid-March, an energetic Coronal Mass Ejection directed toward a clear magnetic channel to Earth led to one of the more intense geomagnetic storms of recent years. A visual result was wide spread auroras being seen over many countries near Earth's magnetic poles. Captured over Kiruna, Sweden, the image features an unusually straight auroral curtain with the green color emitted low in the Earth's atmosphere, and red many kilometers higher up. It is unclear where the rare purple aurora originates, but it might involve an unusual blue aurora at an even lower altitude than the green, seen superposed with a much higher red. As the Sun continues near its top level of surface activity, colorful nights of auroras over Earth are likely to continue.

APOD: 2015 March 19 - Aurora in the Backyard
Explanation: On the night of March 17/18 this umbrella of northern lights unfolded over backyards in Vallentuna, Sweden about 30 kilometers north of Stockholm. A result of the strongest geomagnetic storm of this solar cycle, auroral displays were captured on that night from back and front yards at even lower latitudes, including sightings in the midwestern United States. A boon for aurora hunting skywatchers, the space storm began building when a coronal mass ejection, launched by solar activity some two days earlier, struck planet Earth's magnetosphere. So what's the name of the backyard observatory on the right of the wide field view? That's Carpe Noctem Observatory, of course.

APOD: 2015 March 10 - Aurora over Icelandic Glacier
Explanation: Several key conditions came together to create this award-winning shot. These included a dark night, few clouds, an epic auroral display, and a body of water that was both calm enough and unfrozen enough to show reflected stars. The featured skyscape of activity and serenity appeared over Iceland's Vatnajökull Glacier a year ago January, with the Jökulsárlón Iceberg Lagoon captured in the foreground. Aurora filled skies continue to be common near Earth's poles as our Sun, near Solar Maximum, continues to expel energetic clouds of plasma into the Solar System.

APOD: 2015 February 13 - Aurora on Ice
Explanation: Not from a snowglobe, this expansive fisheye view of ice and sky was captured on February 1, from Jökulsárlón Beach, southeast Iceland, planet Earth. Chunks of glacial ice on the black sand beach glisten in the light of a nearly full moon surrounded by a shining halo. The 22 degree lunar halo itself is created by ice crystals in high, thin clouds refracting the moonlight. Despite the bright moonlight, curtains of aurora still dance through the surreal scene. In early February, their activity was triggered by Earth's restless magnetosphere and the energetic wind from a coronal hole near the Sun's south pole. Bright Jupiter, also near opposition, is visible at the left, beyond the icy lunar halo.

APOD: 2015 February 7 - An Aurora of Marbles
Explanation: It looks like a fine collection of aggies. But this grid of embedded swirls and streaks actually follows the dramatic development of planet Earth's auroral substorms. The sequence of over 600 horizon-to-horizon fisheye images was taken over a 2 hour period near the artic circle in March of 2012 from Lapland, northern Sweden. It begins at upper left in evening twilight and ends at lower right, covering two activity peaks with bright coronae forming overhead. While exploring space between Earth and Moon, NASA's fleet of THEMIS spacecraft discovered that these explosions of auroral activity are driven by sudden releases of energy in the Earth's magnetosphere. Even if you're not playing for keepsies, you can follow this link to check out the sequence in a full timelapse video (vimeo).

APOD: 2014 December 7 - Aurora Shimmer Meteor Flash
Explanation: Northern Lights, or aurora borealis, haunted skies over the island of Kvaløya, near Tromsø Norway on 2009 December 13. This 30 second long exposure records their shimmering glow gently lighting the wintery coastal scene. A study in contrasts, it also captures the sudden flash of a fireball meteor from the excellent Geminid meteor shower in 2009 December. Streaking past familiar stars in the handle of the Big Dipper, the trail points back toward the constellation Gemini, off the top of the view. Both aurora and meteors occur in Earth's upper atmosphere at altitudes of 100 kilometers or so, but aurora caused by energetic charged particles from the magnetosphere, while meteors are trails of cosmic dust. Toward the end of this week the 2014 Geminids meteor shower will peak, although they will compete with the din of last quarter moonlight.

APOD: 2014 November 3 - In Green Company: Aurora over Norway
Explanation: Raise your arms if you see an aurora. With those instructions, two nights went by with, well, clouds -- mostly. On the third night of returning to same peaks, though, the sky not only cleared up but lit up with a spectacular auroral display. Arms went high in the air, patience and experience paid off, and the amazing featured image was captured. The setting is a summit of the Austnesfjorden fjord close to the town of Svolvear on the Lofoten islands in northern Norway. The time was early March. Our Sun has been producing an abundance of picturesque aurora of late as it is near the time of its maximum surface activity in its 11-year magnetic cycle.

APOD: 2014 October 14 - Auroral Corona over Norway
Explanation: Higher than the highest mountain lies the realm of the aurora. Auroras rarely reach below 60 kilometers, and can range up to 1000 kilometers. Aurora light results from energetic electrons and protons striking atoms and molecules in the Earth's atmosphere. Somewhat uncommon, an auroral corona appears as a center point for a surrounding display and may occur when an aurora develops directly overhead, or when auroral rays are pointed nearly toward the observer. This picturesque but brief green and purple aurora exhibition occurred last month high above Kvaløya, Tromsø, Norway. The Sessøyfjorden fjord runs through the foreground, while numerous stars are visible far in the distance.

APOD: 2014 October 3 - Aurora and Milky Way in a Little Sky
Explanation: Stepping stones seem to lead to the Milky Way as it stretches across this little sky. Of course, the scene is really the northern hemisphere's autumnal equinox night. Water and sky are inverted by a top to bottom, around the horizon stereographic projection centered on the zenith above Lake Storsjön in Jämtland, Sweden. In the north the Milky Way arcs from east to west overhead as fall begins, but the season is also a good time for viewing aurora. Geomagnetic storms increase in frequency near the equinox and produce remarkable displays of northern lights at high latitudes, like the eerie greenish glow reflected in this watery cosmos.

APOD: 2014 September 23 - Aurora and Volcanic Light Pillar
Explanation: That's no sunset. And that thin red line just above it -- that's not a sun pillar. The red glow on the horizon originates from a volcanic eruption, and the red line is the eruption's reflection from fluttering atmospheric ice crystals. This unusual volcanic light pillar was captured over Iceland earlier this month. The featured scene looks north from Jökulsárlón toward the erupting volcano Bárðarbunga in the Holuhraun lava field. Even the foreground sky is picturesque, with textured grey clouds in the lower atmosphere, shimmering green aurora in the upper atmosphere, and bright stars far in the distance. Although the last eruption from Holuhraun was in 1797, the present volcanic activity continues.

APOD: 2014 September 17 - Aurora over Maine
Explanation: It has been a good week for auroras. Earlier this month active sunspot region 2158 rotated into view and unleashed a series of flares and plasma ejections into the Solar System during its journey across the Sun's disk. In particular, a pair of Coronal Mass Ejections (CMEs) impacted the Earth's magnetosphere toward the end of last week, creating the most intense geomagnetic storm so far this year. Although power outages were feared by some, the most dramatic effects of these impacting plasma clouds were auroras seen as far south as Wisconsin, USA. In the featured image taken last Friday night, rays and sheets of multicolored auroras were captured over Acadia National Park, in Maine, USA. Since another CME plasma cloud is currently approaching the Earth, tonight offers another good chance to see an impressive auroral display.

APOD: 2014 September 9 - An Aurora Cupcake with a Milky Way Topping
Explanation: This sky looked delicious. Double auroral ovals were captured above the town lights of Östersund, Sweden, last week. Pictured above, the green ovals occurred lower to the ground than violet aurora rays above, making the whole display look a bit like a cupcake. To top it off, far in the distance, the central band or our Milky Way Galaxy slants down from the upper left. The auroras were caused by our Sun ejecting plasma clouds into the Solar System just a few days before, ionized particles that subsequently impacted the magnetosphere of the Earth. Aurora displays may continue this week as an active sunspot group rotated into view just a few days ago.

APOD: 2014 July 22 - Cave with Aurora Skylight
Explanation: Yes, but have you ever seen aurora from a cave? To capture this fascinating juxtaposition between below and above, astrophotographer Bjargmundsson spent much of a night alone in the kilometer-long Raufarhólshellir lava cave in Iceland during late March. There, he took separate images of three parts of the cave using a strobe for illumination. He also took a deep image of the sky to capture faint aurora, and digitally combined the four images later. The 4600-year old lava tube has several skylights under which stone rubble and snow have accumulated. Oh -- the person standing on each mound -- it's the artist.

APOD: 2014 April 29 - Aurora Dog over Alaska
Explanation: Sometimes it is hard to believe what you see in the sky. While leading his annual aurora tour last month near Fairbanks in central Alaska, astrophotographer John Chumack and his company saw a most unusual aurora. This bright aurora appeared to change into the shape of a jumping dog, complete with a curly tail. He was able to capture the fleeting natural apparition in the above image with a 15-second exposure through a wide-angle lens. By coincidence, he also captured a background sky filled with familiar highlights. Planets visible include bright Jupiter through the dog's front legs and reddish Mars below the dog's hind legs. Stars visible include the Big Dipper stars above the dog's midsection and reddish Betelgeuse shining on the far right. This dog would not be following him home, however, and within a few minutes morphed into other shapes before the geomagnetic storm particles that created it shifted to strike the Earth elsewhere.

APOD: 2014 March 24 - Orion and Aurora over Iceland
Explanation: If you see a sky like this -- photograph it. A month ago in Iceland, an adventurous photographer chanced across a sky full of aurora and did just that. In the foreground lies the stratovolcano Öræfajökull. In the background, among other sky delights, lies the constellation of Orion, visible to the aurora's left. Auroras are sparked by energetic particles from the Sun impacting the magnetic environment around the Earth. Resultant energetic particles such as electrons and protons rain down near the Earth's poles and impact the air. The impacted air molecules obtain excited electrons, and when electrons in oxygen molecules fall back to their ground state, they emit green light. Auroras are known to have many shapes and colors.

APOD: 2014 February 26 - Aurora over New Zealand
Explanation: Sometimes the more you look at an image, the more you see. Such may be the case for this beautiful nighttime panorama taken last week in New Zealand. Visible right off, on the far left, are common clouds, slightly altered by the digital fusion of combining 11 separate 20-second exposures. More striking, perhaps, is the broad pink aurora that dominates the right part of the image, a less common auroral color that is likely tinted by excited oxygen atoms high in Earth's atmosphere. Keep looking and you might notice a bright light just beyond the mountain on the left. That is the rising Moon -- and an even closer look will reveal faint crepuscular rays emanating from it. Musing over the image center may cause you to notice the central band of the Milky Way Galaxy which here appears to divide, almost vertically, the left clouds from the right aurora. Inspecting the upper right of the image reveals a fuzzy patch, high in the sky, that is the Small Magellanic Cloud. Numerous stars discretely populate the distant background. Back on Earth, the image foreground features two domes of the Mt. John University Observatory and a camera tripod looking to capture much of this scene over a serene Lake Tekapo.

APOD: 2013 December 28 - Alaska Aurora Sequence
Explanation: A remarkably intense auroral band flooded the northern night with shimmering colors on December 7. The stunning sequence captured here was made with a camera fixed to a tripod under cold, clear skies near Ester, just outside of Fairbanks, Alaska. Left to right, spanning a period of about 30 minutes, the panels follow changes in the dancing curtains of northern lights extending to altitudes of over 100 kilometers in a band arcing directly overhead. The panels span 150 degrees vertically, covering about 500 kilometers of aurora laying across the sky from edge to edge. The auroral activity was triggered by a moderate level geomagnetic storm, as a high speed solar wind stream buffeted planet Earth's magnetosphere.

APOD: 2013 November 18 - Aurora and Unusual Clouds Over Iceland
Explanation: What's happening in the sky? On this cold winter night in Iceland, quite a lot. First, in the foreground, lies the largest glacier in Iceland: Vatnajokull. On the far left, bright green auroras appear to emanate from the glacier as if it was a volcano. Aurora light is reflected by the foreground lake Jökulsárlón. On the far right is a long and unusual lenticular cloud tinged with green light emitted from another aurora well behind it. Just above this lenticular cloud are unusual iridescent lenticular clouds displaying a broad spectral range of colors. Far beyond the lenticular is the setting Moon, while far beyond even the Moon are setting stars. The above image was captured in late March of 2012.

APOD: 2013 November 6 - Creature Aurora Over Norway
Explanation: It was Halloween and the sky looked like a creature. Exactly which creature, the astrophotographer was unsure (but possibly you can suggest one). Exactly what caused the eerie apparition was sure: one of the best auroral displays in recent memory. This spectacular aurora had an unusually high degree of detail. Pictured above, the vivid green and purple auroral colors are caused by high atmospheric oxygen and nitrogen reacting to a burst of incoming electrons. Birch trees in Tromsø, Norway formed an also eerie foreground. Many other photogenic auroras have been triggered by recent energetic flares on the Sun.

APOD: 2013 October 5 - October Aurora in Prairie Skies
Explanation: Wind and spaceweather are transformed in this haunting night skyscape. The prairie windmill and colorful auroral display were captured on October 1, from central South Dakota, USA, as a good season for aurora hunters came with longer autumn nights. From green to rarer reddish hues, the northern lights are sparked by the geomagnetic storms caused by solar activity. These extend far above the cloud bank to altitudes well over 100 kilometers, against the backdrop of distant stars in the northern night. Visual double star Mizar, marking the middle of the Big Dipper's handle, is easy to spot at the left edge of the frame. The dipper's North Celestial Pole pointers Merak and Dubhe line up vertically near picture center.

APOD: 2013 August 19 - Noctilucent Clouds and Aurora Over Scotland
Explanation: Why would the sky still glow after sunset? Besides stars and the band of our Milky Way galaxy, the sky might glow because it contains either noctilucent clouds or aurora. Rare individually, both are visible in the above time lapse movie taken over Caithness, Scotland, UK taken during a single night earlier this month. First noted in 1885, many noctilucent clouds are known to correlate with atmospheric meteor trails, although details and the origins of others remain a topic of research. These meandering bright filaments of sunlight-reflecting ice crystals are the highest clouds in the Earth's atmosphere. The above video captures not only a variety of noctilucent clouds, but also how their structure varies over minutes. Lower clouds typically appear dark or fast moving. About halfway through the video the clouds are joined by aurora. At times, low clouds, noctilucent clouds, and aurora are all visible simultaneously, each doing their own separate dance, and once -- see if you can find it -- even with the Big Dipper rotating across the background.

APOD: 2013 June 9 - Flowing Auroras Over Norway
Explanation: Have you ever seen an aurora? Auroras are occurring again with increasing frequency. With the Sun peaking at its eleven year maximum in aurora-triggering activity, it is exhibiting a greater abundance of sunspots, flares, and coronal mass ejections. Solar activity like this typically expels charged particles into the Solar System, some of which impact Earth's magnetosphere and trigger Earthly auroras. In late 2010, the above timelapse displays of picturesque auroras were captured above Tromsø, Norway. Curtains of auroral light, usually green, flow, shimmer and dance as energetic particles fall toward the Earth and excite atoms of air high up in the Earth's atmosphere. There may even be opportunities to see auroras tonight, as recent solar explosions have triggered numerous aurora sightings over the past few days.

APOD: 2013 May 22 - Red Sprite Lightning with Aurora
Explanation: What's that in the sky? It is a rarely seen form of lightning confirmed only about 25 years ago: a red sprite. Recent research has shown that following a powerful positive cloud-to-ground lightning strike, red sprites may start as 100-meter balls of ionized air that shoot down from about 80-km high at 10 percent the speed of light and are quickly followed by a group of upward streaking ionized balls. The above image, taken a few days ago above central South Dakota, USA, captured a bright red sprite, and is a candidate for the first color image ever recorded of a sprite and aurora together. Distant storm clouds cross the bottom of the image, while streaks of colorful aurora are visible in the background. Red sprites take only a fraction of a second to occur and are best seen when powerful thunderstorms are visible from the side.

APOD: 2013 February 12 - Reflected Aurora Over Alaska
Explanation: Some auroras can only be seen with a camera. They are called subvisual and are too faint to be seen with the unaided eye. In the above image, the green aurora were easily visible to the eye, but the red aurora only became apparent after a 20-second camera exposure. The reason is that the human eye only accumulates light for a fraction of a second at a time, while a camera shutter can be left open much longer. When photographing an already picturesque scene near Anchorage, Alaska, USA, last autumn, a camera caught both the visual green and subvisual red aurora reflected in a lily pad-covered lake. High above, thousands of stars were visible including the Pleiades star cluster, while the planet Jupiter posed near the horizon, just above clouds, toward the image right. Auroras are caused by energetic particles from the Sun impacting the Earth's magnetosphere, causing electrons and protons to rain down near the Earth's poles and impact the air. Both red and green aurora are typically created by excited oxygen atoms, with red emission, when visible, dominating higher up. Auroras are known to have many shapes and colors.

APOD: 2012 October 17 - Aurora Over White Dome Geyser
Explanation: Sometimes both heaven and Earth erupt. Colorful aurorae erupted unexpectedly earlier this month, with green aurora appearing near the horizon and brilliant bands of red aurora blooming high overhead. A bright Moon lit the foreground of this picturesque scene, while familiar stars could be seen far in the distance. With planning, the careful astrophotographer shot this image mosaic in the field of White Dome Geyser in Yellowstone National Park in the western USA. Sure enough, just after midnight, White Dome erupted -- spraying a stream of water and vapor many meters into the air. Geyser water is heated to steam by scalding magma several kilometers below, and rises through rock cracks to the surface. About half of all known geysers occur in Yellowstone National Park. Although the geomagnetic storm that created these aurorae has since subsided, eruptions of White Dome Geyser continue about every 30 minutes.

APOD: 2012 October 5 - Aurora and Fireball Over Norway
Explanation: What's happening behind that mountain? A convergence of variable sky spectacles. One night in mid-September near Tromsø, Norway, high red aurora could be seen shimmering through lower green aurora in a way that created a striking and somewhat unusual violet glow. Suddenly, though, the sky flashed with the brightest fireball the astrophotographer had ever seen, as a small pebble from outer space violently crashed into the Earth's atmosphere. The glow illuminated the distant mountain peak known as Otertinden of the Lyngen Alps. The bright meteor, which coincidently disappeared behind the same mountain, was also reflected in the foreground Signalelva River. Although you might consider yourself lucky to see either an aurora or a bright meteor, pictures of them together have been recorded several times previously.

APOD: 2012 October 3 - Goat Aurora Over Greenland
Explanation: Sometimes it's hard to believe what you see in the sky. During the Shelios Expedition to Greenland in late August, even veteran sky enthusiasts saw auroras so colorful, so fast changing, and so unusual in form that they could remember nothing like it. As the ever changing auroras evolved, huge shapes spread across the sky morphed from one familiar form into another, including what looked to be the head of a goat (shown above), the head of an elephant, a strange green-tailed comet, and fingers on a celestial hand. Even without the aurora, the sky would be notable for the arching band of our Milky Way Galaxy and the interesting field of stars, nebulas, and galaxies. In contrast, in the foreground is a farm house in Tasiusaq, Kujalleq. Greenland. The Shelios project exists not only to observe auroras but to motivate students to consider a career in science.

APOD: 2012 September 21 - September Aurora
Explanation: September's equinox arrives tomorrow as the Sun crosses the celestial equator heading south. The event marks the astronomical beginning of spring in the southern hemisphere and autumn in the north. And though the connection is still puzzling, the equinox seasons bring an increase in geomagnetic storms. So as northern nights grow longer, the equinox also heralds the arrival of a good season for aurora hunters. Recorded on September 20, these colorful northern lights were captured with camera and wide-angle lens near the Norwegian Sea coast outside Tromsø in Northern Norway. Shining at altitudes of 100 kilometers or so, the aurora rays are parallel, but perspective makes them appear to radiate from a vanishing point behind the silhouetted pine tree. Stars in this enchanting northern night include Polaris above and right of the tree top, and yellowish giant stars Shedar (Alpha Cassiopiae) to the left and Kochab (Beta Ursae Minoris) to the right. Bright Altair shines through the greenish auroral curtain at the lower left of the scene.

APOD: 2012 July 25 - Pink Aurora Over Crater Lake
Explanation: Why is this aurora strikingly pink? When photographing picturesque Crater Lake in Oregon, USA last month, the background sky lit up with auroras of unusual colors. Although much is known about the physical mechanisms that create auroras, accurately predicting the occurrence and colors of auroras remains a topic of investigation. Typically, it is known, the lowest auroras appear green. These occur at about 100 kilometers high and involve atmospheric oxygen atoms excited by fast moving plasma from space. The next highest auroras -- at about 200 kilometers up -- appear red, and are also emitted by resettling atmospheric oxygen. Some of the highest auroras visible -- as high as 500 kilometers up -- appear blue, and are caused by sunlight-scattering nitrogen ions. When looking from the ground through different layers of distant auroras, their colors can combine to produce unique and spectacular hues, in this case rare pink hues seen above. As Solar Maximum nears over the next two years, particle explosions from the Sun are sure to continue and likely to create even more memorable nighttime displays.

APOD: 2012 July 8 - Volcano and Aurora in Iceland
Explanation: Sometimes both heaven and Earth erupt. In Iceland in 1991, the volcano Hekla erupted at the same time that auroras were visible overhead. Hekla, one of the most famous volcanoes in the world, has erupted at least 20 times over the past millennium, sometimes causing great destruction. The last eruption occurred only twelve years ago but caused only minor damage. The green auroral band occurred fortuitously about 100 kilometers above the erupting lava. Is Earth the Solar System's only planet with both auroras and volcanos?

APOD: 2012 April 30 - Aurora Over Raufarhöfn
Explanation: It was all lined up even without the colorful aurora exploding overhead. If you follow the apex line of the recently deployed monuments of Arctic Henge in Raufarhöfn in northern Iceland from this vantage point, you will see that they point due north. A good way to tell is to follow their apex line to the line connecting the end stars of the Big Dipper, Merak and Dubhe, toward Polaris, the bright star near the north spin axis of the Earth projected onto the sky. By design, from this vantage point, this same apex line will also point directly at the midnight sun at its highest point in the sky just during the summer solstice of Earth's northern hemisphere. In other words, the Sun will not set at Arctic Henge during the summer solstice in late June, and at its highest point in the sky it will appear just above the aligned vertices of this modern monument. The above image was taken in late March during a beautiful auroral storm.

APOD: 2012 March 21 - Aurora Over Iceland
Explanation: If you see a sky like this -- photograph it. Three nights ago in Iceland, an adventurous photographer (pictured) chanced across a sky full of aurora and did just that. Afterwards, by stitching together five smaller photographs, the entire aurora-lit sky was recreated in this 180-degree panorama taken from Vatnajökull glacier. Auroras are sparked by energetic particles from the Sun impacting the magnetic environment around the Earth. Resultant energetic particles such as electrons and protons rain down near the Earth's poles and impact the air. The impacted air molecules obtain excited electrons, and when electrons in oxygen molecules fall back to their ground state, they emit green light. Auroras are known to have many shapes and colors.

APOD: 2012 February 9 - Trees, Stars, Aurora
Explanation: Have you ever seen an aurora? Auroras are occurring again with increasing frequency. With the Sun being unusually dormant over the past four years, the amount of Sun-induced auroras has been unusually low. More recently, however, our Sun has become increasingly active and exhibiting a greater abundance of sunspots, flares, and coronal mass ejections. Solar activity like this typically expels charged particles into the Solar System, some of which may trigger Earthly auroras. Two weeks ago, beyond trees and before stars, a solar storm precipitated the above timelapse displays of picturesque auroras above Ravnastua, Skoganvarre and Lakselv, Norway. Curtains of auroral light, typically green, flow, shimmer and dance as energetic particles fall toward the Earth and excite air molecules high up in the Earth's atmosphere. With solar maximum still in the future, there may be even better opportunities to see spectacular auroras personally over the next few years.

APOD: 2012 February 1 - Red Aurora Over Australia
Explanation: Why would the sky glow red? Aurora. Last week's solar storms, emanating mostly from active sunspot region 1402, showered particles on the Earth that excited oxygen atoms high in the Earth's atmosphere. As the excited element's electrons fell back to their ground state, they emitted a red glow. Were oxygen atoms lower in Earth's atmosphere excited, the glow would be predominantly green. Pictured above, this high red aurora is visible just above the horizon last week near Flinders, Victoria, Australia. The sky that night, however, also glowed with more familiar but more distant objects, including the central disk of our Milky Way Galaxy on the left, and the neighboring Large and Small Magellanic Cloud galaxies on the right. A time-lapse video highlighting auroras visible that night puts the picturesque scene in context. Why the sky did not also glow green remains unknown.

APOD: 2012 January 28 - Planet Aurora Borealis
Explanation: Illuminated by an eerie greenish light, this remarkable little planet is covered with ice and snow and ringed by tall pine trees. Of course, this little planet is actually planet Earth, and the surrounding stars are above the horizon near Östersund, Sweden. The pale greenish illumination is from a curtain of shimmering Aurora Borealis also known as the Northern Lights. The display was triggered when a giant solar coronal mass ejection (CME) rocked planet Earth's magnetosphere on January 24th and produced a strong geomagnetic storm. Northern hemisphere skygazers will also recognize the familiar orientation of stars at the left, including the Pleiades and Hyades star clusters and the stars of Orion. Increasing solar activity has caused recent auroral displays to be wide spread, including Aurora Australis, the Southern Lights, at high southern latitudes.

APOD: 2012 January 24 - January Aurora Over Norway
Explanation: What's that in the sky? An aurora. A large coronal mass ejection occurred on our Sun five days ago, throwing a cloud of fast moving electrons, protons, and ions toward the Earth. Although most of this cloud passed above the Earth, some of it impacted our Earth's magnetosphere and resulted in spectacular auroras being seen at high northern latitudes. Pictured above is a particularly photogenic auroral corona captured last night above Grotfjord, Norway. To some, this shimmering green glow of recombining atmospheric oxygen might appear as a large eagle, but feel free to share what it looks like to you. This round of solar activity is not yet over -- a new and even more powerful solar flare occurred yesterday that might provide more amazing aurora as soon as tonight.

APOD: 2012 January 3 - A Full Sky Aurora Over Norway
Explanation: Higher than the highest building, higher than the highest mountain, higher than the highest airplane, lies the realm of the aurora. Auroras rarely reach below 60 kilometers, and can range up to 1000 kilometers. Aurora light results from energetic electrons and protons striking molecules in the Earth's atmosphere. Frequently, when viewed from space, a complete aurora will appear as a circle around one of the Earth's magnetic poles. The above wide angle image, horizontally compressed, captured an unexpected auroral display that stretched across the sky one month ago over eastern Norway.

APOD: 2011 December 5 - A Memorable Aurora Over Norway
Explanation: It was one of the most memorable auroras of the season. There was green light, red light, and sometimes a mixture of the two. There were multiple rays, distinct curtains, and even an auroral corona. It took up so much of the sky. In the background were stars too numerous to count, in the foreground a friend trying to image the same sight. The scene was captured with a fisheye lens around and above Tromsø, Norway, last month. With the Sun becoming more active, next year might bring even more spectacular aurora.

APOD: 2011 November 14 - Waterfall, Moonbow, and Aurora from Iceland
Explanation: The longer you look at this image, the more you see. Perhaps your eye is first drawn to the picturesque waterfall called Skogarfoss visible on the image right. Just as prevalent, however, in this Icelandic visual extravaganza, is the colorful arc of light on the left. This chromatic bow is not a rainbow, since the water drops did not originate in rainfall nor are they reflecting light from the Sun. Rather, the drops have drifted off from the waterfall and are now illuminated by the nearly full Moon. High above are the faint green streaks of aurora. The scene, captured one night last month, also shows a beautiful starscape far in the background, including the Big Dipper, part of the constellation of the Great Bear (Ursa Major).

APOD: 2011 September 23 - September's Aurora
Explanation: September's equinox arrives today at 0905 UT. As the Sun crosses the celestial equator heading south, spring begins in the southern hemisphere and autumn in the north. And though the seasonal connection is still puzzling, both spring and autumn bring an increase in geomagnetic storms. So as northern nights grow longer, the equinox also heralds the arrival of a good season for viewing aurora. Recorded earlier this month, these curtains of September's shimmering green light sprawl across a gorgeous night skyscape. In the foreground lies Hidden Lake Territorial Park near Yellowknife, Northwest Territories, Canada. Calm water reflects the aurora, with bright star trails peering through the mesmerizing sky glow. Of course, shining at altitudes of 100 kilometers or so, planet Earth's auroras are visible from space.

APOD: 2011 August 23 - Aurora Over Greenland
Explanation: This aurora arched from horizon to horizon. During the current Shelios expedition to observe and learn about the northern lights, the sky last weekend did not disappoint. After sunset and some careful photographic planning, the above image was taken from the expedition's Qaleraliq campsite in southern Greenland. Visible straight through the center of the aurora, found with a careful eye, is the Big Dipper and the surrounding constellation of the Big Bear (Ursa Major). The brightest orb on the far right is the Moon, while Jupiter can be seen even further to the right. The Shelios expedition is scheduled to last until the end of August and include live broadcasts of ongoing auroras.

APOD: 2010 November 24 - Flowing Auroras Over Norway
Explanation: Have you ever seen an aurora? Auroras are occurring again with increasing frequency. With the Sun being unusually dormant over the past three years, the amount of Sun-induced auroras has also been unusually low. More recently, however, our Sun has become increasingly active and exhibiting a greater abundance of sunspots, flares, and coronal mass ejections. Solar activity like this typically expels charged particles into the Solar System, some of which may trigger Earthly auroras. As this year unfolded, the above timelapse displays of picturesque auroras were captured above Tromsø, Norway. Curtains of auroral light, usually green, flow, shimmer and dance as energetic particles fall toward the Earth and ionize air molecules high up in the Earth's atmosphere. With solar maximum still in the future, there may be opportunities to see spectacular aurora personally over the next three years.

APOD: 2010 October 6 - Aurora Over Alaska
Explanation: Are those green clouds or aurora? Photographed above two weeks ago, puffy green aurora help the Moon illuminate the serene Willow Lake and the snowy Wrangell and Saint Elias Mountains in eastern Alaska, USA. Although auroras might first appear to be moonlit clouds, they only add light to the sky and do not block background stars from view. Called northern lights in the northern hemisphere, auroras are caused by collisions between charged particles from the magnetosphere and air molecules high in the Earth's atmosphere. If viewed from space, auroras can be seen to glow in X-ray and ultraviolet light as well. Predictable auroras likely occur a few days after a powerful magnetic event has been seen on the Sun.

APOD: 2010 September 20 - Aurora Over Norway
Explanation: Auroras can make spectacular sights. Photographed above last weekend, flowing multi-colored auroras helped illuminate a busy sky above Tromsø, Norway. Besides the spectacular aurora pictured above, the photographer caught three satellites streaks, one airplane streak, and a friend trying to capture the same sight. Although auroras might first appear to be moonlit clouds, they only add light to the sky and do not block background stars from view. Called northern lights in the northern hemisphere, auroras are caused by collisions between charged particles from the magnetosphere and air molecules high in the Earth's atmosphere. If viewed from space, auroras can be seen to glow in X-ray and ultraviolet light as well. Predictable auroras might occur a few days after a powerful magnetic event has been seen on the Sun.

APOD: 2010 September 17 - Northern Lights over Prelude Lake
Explanation: Curtains of shimmering green light sprawl across this gorgeous night skyscape. In the foreground lies the peaceful Prelude Lake, located about 30 kilometers east of Yellowknife, Northwest Territories, Canada. From high northern latitudes these mesmerizing northern lights, also known as the aurora borealis, are becoming a more familiar sight. As the September 23rd equinox approaches, nights grow longer and a favorable season for aurora begins. Recorded on September 11, this panoramic scene spans about 180 degrees. Brighter stars peering through the auroral glow at the left form the recognizable northern asterism, the Big Dipper. A more compact Pleiades star cluster shines at the far right.

APOD: 2010 July 1 - Above Aurora Australis
Explanation: On May 29, looking southward from a vantage point about 350 kilometers above the southern Indian Ocean, astronauts onboard the International Space Station watched this enormous, green ribbon shimmering below. Known as aurora australis or southern lights, the shifting, luminous bands are commonly seen at high northern latitudes as well, there known as the aurora borealis or northern lights. North or south their cause is the same though, as energetic charged particles from the magnetosphere pile into the atmosphere near the Earth's poles. To produce the characteristic greenish glow, the energetic particles excite oxygen atoms at altitudes of 100 kilometers or more. Aurora on May 29 were likely triggered by the interaction of the magnetosphere with a coronal mass ejection erupting from the Sun on May 24.

APOD: 2010 March 11 - Yukon Aurora with Star Trails
Explanation: Fixed to a tripod, a camera can record graceful trails traced by stars as planet Earth rotates on its axis. But at high latitudes during March and April, it can also capture an aurora shimmering in the night. In fact, the weeks surrounding the equinox, in both spring and fall, offer a favorable season for aurora hunters. The possibilities are demonstrated in this beautiful moonlit vista from northwestern Canadian territory the Yukon. It was taken during the early morning of March 1, off the Klondike Highway about 60 kilometers south of Dawson City. To compose the picture, many short exposures were digitally combined to follow the concentric star trail arcs while including the greenish auroral curtains also known as the northern lights.

APOD: 2009 December 19 - Aurora Shimmer, Meteor Flash
Explanation: Northern Lights, or aurora borealis, haunted skies over the island of Kvaløya, near Tromsø Norway on December 13. This 30 second long exposure records their shimmering glow gently lighting the wintery coastal scene. A study in contrasts, it also captures the sudden flash of a fireball meteor from December's excellent Geminid meteor shower. Streaking past familiar stars in the handle of the Big Dipper, the trail points back toward the constellation Gemini, off the top of the view. Both aurora and meteors occur in Earth's upper atmosphere at altitudes of 100 kilometers or so, but aurora are caused by energetic charged particles from the magnetosphere, while meteors are trails of cosmic dust.

APOD: 2009 September 22 - Aurora Over Yellowknife
Explanation: Sometimes, after your eyes adapt to the dark, a spectacular sky appears. In this case, a picturesque lake lies in front of you, beautiful green auroras flap high above you, brilliant stars shine far in the distance, and a brilliant moon shines just ahead of you. This digitally fused panorama was captured earlier this month from Yellowknife, Northwest Territories, Canada, and includes the Pleiades open cluster of stars just to the upper right of the Moon. Since auroras are ultimately started by solar activity, this current flurry of auroras is somewhat surprising, given the historic lack of sunspots and other activity on the Sun over the past two years. This time of year is known as aurora season, however, for noted average increases in auroras. The reason for the yearly increase is not known for sure, but possibly relates to the tilt of the Earth creating a more easily traversable connection between the Earth's magnetic field and the magnetic field of the Sun's changing wind streams.

APOD: 2009 July 28 - A Floral Aurora Corona
Explanation: Few auroras show this level of detail. Above, a standard digital camera captured a particularly active and colorful auroral corona that occurred last week above Alberta, Canada. With a shape reminiscent of a flower, the spectacular aurora had an unusually high degree of detail. The vivid green and purple auroral colors are caused by high atmospheric oxygen and hydrogen reacting to a burst of incoming electrons. Many photogenic auroras have been triggered from a solar wind stream that recently passed the Earth. The auroras were unexpected because the initiating Sun has been unusually quiet of late.

APOD: 2009 February 1 - Auroral Corona Over Norway
Explanation: Higher than highest communications tower, higher than highest mountain, higher than highest airplane, lies the realm of the aurora. Auroras rarely reach below 60 kilometers, and can range up to 1000 kilometers. Aurora light results from energetic electrons and protons striking molecules in the Earth's atmosphere. Frequently, when viewed from space, a complete aurora will appear as a circle around one of the Earth's magnetic poles. This particularly rare purple auroral corona occurred in 2004 high above Harstad, Norway.

APOD: 2008 November 19 - Unusual Auroras Over Saturns North Pole
Explanation: What's causing this unusual aurora over Saturn? No one is sure. Infrared images by the robotic Cassini spacecraft of the north pole of Saturn have uncovered aurora unlike any other seen previously in our Solar System. The strange aurora are shown in blue in the above image, while the underlying clouds are shown in red. The previously recorded, also-strange hexagon cloud patterns are visible in red below the aurora. These Saturnian aurora can cover the entire pole, while auroras around Earth and Jupiter are typically confined by magnetic fields to rings surrounding the magnetic poles. More normal auroral rings had been previously imaged around Saturn. The recently imaged strange auroras above Saturn's north pole can change their global patterns significantly in only a few minutes. The large and variable nature of these auroras indicate that charged particles streaming in from the Sun are experiencing some type of magnetism above Saturn that was previously unexpected.

APOD: 2008 August 9 - Aurora Persei
Explanation: Dark skies are favored for viewing meteor showers -- so the best viewing of this year's Perseids will occur in the early morning. While the Perseid meteor shower is scheduled to peak over the next few days, bright light from a gibbous Moon will also flood the early evening and mask the majority of relatively faint meteors. Still, skygazing in the early morning after the Moon sets (after about 2 AM local time) could reveal many faint meteors. Persistant observing at any time after sunset can reward northern hemisphere watchers looking for occasional Perseid fireballs. Astronomer Jimmy Westlake imaged this bright Perseid meteor despite the combination of moonlight and auroral glow over Colorado skies in August of 2000.

APOD: 2008 January 7 - Quadrantid Meteors and Aurora from the Air
Explanation: Where do meteor showers originate? To help answer this question, astronomers studied in some detail the Quadrantid meteor shower that occurred over this past weekend. In particular, astronomers with specialized cameras flew as part of the Quadrantid's Multi-Instrument Aircraft Campaign (MAC) aboard a Gulfstream V aircraft above northern Canada over the past few days and studied the Quadrantid meteor shower in unprecedented detail. Pictured above is a composite image combining many short exposures. Visible in the image are the wingtip of the airplane reflecting a red beacon on the left, green aurora most prominent on the image right, and numerous meteor streaks throughout. Preliminary indications are that the meteor stream is quite stable in time but variable in meteor abundance. Over 100 meteors per hour were visible at the peak from the MAC aircraft. Meteor data from around the world will continue to be analyzed to try to verify Peter Jenniskens's recent hypothesis that minor planet 2003 EH1 is an intermittently active comet and the parent body of the annual Quadrantid meteor shower.

APOD: 2008 January 1 - Rays from an Unexpected Aurora
Explanation: This aurora was a bit of a surprise. For starters, on this day in 2002, no intense auroral activity was expected at all. Possibly more surprising, however, the aurora appeared to show an usual structure of green rays from some locations. In this view, captured from North Dakota, USA, a picket fence of green rays stretches toward the horizon. Mirroring the green rays is a red band, somewhat rare in its own right. Lights from the cities of Bismarck and Mandan are visible near the horizon.

APOD: 2007 November 19 - Aurora in the Distance
Explanation: Some auroras can only be seen with a camera. They are called sub-visual and are too faint to be seen with the unaided eye. The reason is that the human eye only accumulates light for a fraction of a second at a time, while a camera shutter can be left open indefinitely. When photographing an already picturesque scene above Juneau, Alaska, USA, a camera caught green sub-visual aurora near the horizon. Auroras are sparked by energetic particles from the Sun impacting the magnetic environment around the Earth. Resultant energetic particles such as electrons and protons rain down near the Earth's poles and impact the air. The impacted air molecules temporarily lose electrons, and when oxygen molecules among them reacquire these electrons, they emit green light. Auroras are known to have many shapes and colors.

APOD: 2007 October 9 - Aurora, Stars, Meteor, Lake, Alaska
Explanation: Sometimes, after your eyes adapt to the dark, a spectacular sky appears. In this case, a picturesque lake lies in front of you, beautiful green aurora flap high above you, brilliant stars shine far in the distance, and, for a brief moment, a bright meteor streaks by. This digitally fused breathtaking panorama was captured late last month across one of the Chena Lakes in North Pole, Alaska, USA, and includes the Pleiades open cluster of stars on the image right. The shot is unusual not only for the many wonders it has captured simultaneously, but because lakes this far north tend to freeze and become non-reflecting before a sky this dark can be photographed.

APOD: 2007 July 15 - Aurora from Space
Explanation: From the ground, spectacular auroras seem to dance high above. But the International Space Station (ISS) orbits at nearly the same height as many auroras, sometimes passing over them, and sometimes right through them. Still, the auroral electron and proton streams pose no direct danger to the ISS. In 2003, ISS Science Officer Don Pettit captured the green aurora, pictured above in a digitally sharpened image. From orbit, Pettit reported that changing auroras appeared to crawl around like giant green amoebas. Over 300 kilometers below, the Manicouagan Impact Crater can be seen in northern Canada, planet Earth.

APOD: 2007 April 9 - Aurora Over Alaska
Explanation: Higher than the highest mountain, higher than the highest airplane, lies the realm of the aurora. Aurora rarely reach below 60 kilometers, and can range up to 1000 kilometers. Aurora light results from solar shockwave causing energetic electrons and protons to striking molecules in the Earth's atmosphere. Frequently, when viewed from space, a complete aurora will appear as a circle around one of the Earth's magnetic poles. The above digitally enhanced photograph was taken in 2005 January shows a spectacular aurora borealis above the frozen landscape of Bear Lake, Alaska, USA. The above image was voted Wikipedia Commons Picture of the Year for 2006.

APOD: 2006 December 18 - Aurora Over Iowa
Explanation: Last Thursday evening, stars were not the only lights in Iowa skies. Spectacular northern lights also shone from the heavens, extending across the midwestern USA and other locations not often graced with auroral displays. The wide-ranging auroral activity was triggered as a large solar flare - an energetic cloud of particles blasted outward from the Sun a few days earlier - collided with planet Earth's magnetosphere. Alerted to conditions ripe for aurora, photographer Stan Richard recorded this apparition over Saylorville Lake, near Des Moines, Iowa, USA. While the colorful rays seem to end just above the water, they are actually at altitudes of 100 kilometers or more.

APOD: 2006 September 6 - Green Aurora Over Lake Superior
Explanation: What if your horizon was green? If you've got a camera, take a picture! That was the experience of Jeff Hapeman last week when visiting the Pictured Rocks National Lakeshore in Michigan. On a quiet night toward the northern horizon over Lake Superior was a long lasting diffuse green aurora. The above image was taken in an effort to capture the sense of wonder one gets when watching an auroral display. Auroras are sparked by energetic particles from the Sun impacting the magnetic environment around the Earth. Resultant energetic particles such as electrons and protons rain down near the Earth's poles and impact the air. The impacted air molecules temporarily lose electrons, and when oxygen molecules among them reacquire these electrons, they emit green light. Auroras are known to have many shapes and colors.

APOD: 2006 March 29 - Green and Black Auroras Over Norway
Explanation: What causes gaps between aurora curtains? These unusual gaps can make auroral displays appear more detailed and intricate. Research using data from four Cluster spacecraft orbiting the Earth has likely found the secret: auroral gaps, sometimes knows as black auroras, are actually anti-auroras. In normal auroras, electrons and/or predominantly negatively charged particles fall toward Earth along surfaces of constant magnetic field. They ionize the Earth's atmosphere on impact, causing the bright glows. In auroral gaps, however, negatively charged particles may be sucked out from the Earth's ionosphere along adjoining magnetic field lines. These dark anti-auroras can climb to over 20,000 kilometers and last for several minutes. Pictured above, a series of well-defined auroral gaps is seen dividing green aurora curtains high above Harstad, Norway, earlier this month.

APOD: 2006 March 5 - Colorful Light Pillars
Explanation: How can an aurora appear so near the ground? Pictured above are not aurora but nearby light pillars, a local phenomenon that can appear as a distant one. In most places on Earth, a lucky viewer can see a Sun-pillar, a column of light appearing to extend up from the Sun caused by flat fluttering ice-crystals reflecting sunlight from the upper atmosphere. Usually these ice ice crystals evaporate before reaching the ground. During freezing temperatures, however, flat fluttering ice crystals may form near the ground in a form of light snow, sometimes known as a crystal fog. These ice crystals may then reflect ground lights in columns not unlike a Sun-pillar. In the above picture, the colorful lights causing the light pillars surround a ice-skating rink in Fairbanks, Alaska.

APOD: 2006 January 29 - Volcano and Aurora in Iceland
Explanation: Sometimes both heaven and Earth erupt. In Iceland in 1991, the volcano Hekla erupted at the same time that auroras were visible overhead. Hekla, one of the most famous volcanoes in the world, has erupted at least 20 times over the past millennium, sometimes causing great destruction. The last eruption occurred only six years ago but caused only minor damage. The green auroral band occurred fortuitously about 100 kilometers above the erupting lava. Is Earth the Solar System's only planet with both auroras and volcanos?

APOD: 2005 November 20 - Rays from an Unexpected Aurora
Explanation: This aurora was a bit of a surprise. For starters, on this Friday morning in August 2002, no intense auroral activity was expected at all. Possibly more surprising, however, the aurora appeared to show an usual structure of green rays from some locations. In the above image, captured from North Dakota, USA, a picket fence of green rays stretches toward the horizon. Mirroring the green rays is a red band, somewhat rare in its own right. Lights from the cities of Bismarck and Mandan are visible near the horizon. Large sunspot groups indicate that activity from an active Sun is relatively likely, possibly causing other streams of energetic particles to cascade onto the Earth and so causing more auroras.

APOD: 2005 November 5 - Aurora from Space
Explanation: From the ground, spectacular auroras seem to dance high above. But the International Space Station (ISS) orbits at nearly the same height as many auroras, sometimes passing over them, and sometimes right through them. Still, the auroral electron and proton streams pose no direct danger to the ISS. In 2003, ISS Science Officer Don Pettit captured the green aurora, pictured above in a digitally sharpened image. From orbit, Pettit reported that changing auroras appeared to crawl around like giant green amoebas. Over 300 kilometers below, the Manicouagan Impact Crater can be seen in northern Canada, planet Earth.

APOD: 2005 September 16 - Northern Lights, September Skies
Explanation: So far, the Aurora Borealis or Northern Lights have made some remarkable visits to September's skies. The reason, of course, is the not-so-quiet Sun. In particular, a large solar active region now crossing the Sun's disk has produced multiple, intense flares and a large coronal mass ejection (CME) that triggered wide spread auroral activity just last weekend. This colorful example of spectacular curtains of aurora was captured with a fish-eye lens in skies over Quebec, Canada on September 11. Also featured is the planet Mars, the brightest object above and left of center. Seen near Mars (just below and to the right) is the tightly knit Pleiades star cluster. Although they can appear to be quite close, the northern lights actually originate at extreme altitudes, 100 kilometers or so above the Earth's surface.

APOD: 2005 May 20 - Aurora Iowa
Explanation: Early last Sunday morning stars were not the only lights in Iowa skies. The northern lights also shone from the heavens, extending across the midwestern USA and other locations not often graced with auroral displays. The wide-ranging auroral activity was triggered as a coronal mass ejection - an energetic cloud of particles blasted outward from the Sun a few days earlier - collided with planet Earth's magnetosphere. Alerted to conditions ripe for aurora, photographer Stan Richard recorded this aparition over Saylorville Lake, near Des Moines. Bright planet Mars in the constellation Aquarius is above the horizon near the center of the eastward-looking view. While the colorful rays seem to end just above the water, they are actually at altitudes of 100 kilometers or more.

APOD: 2005 February 19 - Saturnian Aurora
Explanation: Saturn's Rings are one of the most spectacular sights in the solar system. Still, this image from the Hubble Space Telescope offers a striking view of another kind of ring around Saturn - pole encircling rings of ultraviolet aurora. Towering more than 1,000 miles above the cloud tops, these Saturnian auroral displays were thought to be analogous to Earth's. But following the ebb and flow of Saturn's aurora, with the Hubble's cameras and instruments onboard the Cassini spacecraft, researchers are now reporting some surprising results. In this false-color image made in ultraviolet light, the dramatic red aurora identify emission from atomic hydrogen, while the more concentrated white areas are due to hydrogen molecules.

APOD: 2004 November 17 - Aurora Over Wisconsin
Explanation: The auroral displays of the past week are being reported as some of the most beautiful in memory. In particular, impressive auroral bands fanned out over much of eastern North America after sunset on November 8. The multicolored aurora pictured above was caught reflecting in one of the many small lakes in central Wisconsin near that time. Continued solar activity might create more aurora visible over the next few nights as the Leonids meteor shower peaks.

APOD: 2004 September 28 - Aurora Over a Communications Tower
Explanation: Higher than highest communications tower, higher than highest mountain, higher than highest airplane, lies the realm of the aurora. Auroras rarely reach below 60 kilometers, and can range up to 1000 kilometers. Aurora light results from energetic electrons and protons striking molecules in the Earth's atmosphere. Frequently, when viewed from space, a complete aurora will appear as a circle around one of the Earth's magnetic poles. Pictured above is a particularly rare purple auroral corona that occurred on August 30, high above Harstad, Norway.

APOD: 2004 June 13 - Volcano and Aurora in Iceland
Explanation: Sometimes both heaven and Earth erupt. In Iceland in 1991, the volcano Hekla erupted at the same time that auroras were visible overhead. Hekla, one of the most famous volcanoes in the world, has erupted at least 20 times over the past millennium, sometimes causing great destruction. The last eruption occurred only two years ago but caused only minor damage. The green auroral band occurred fortuitously about 100 kilometers above the erupting lava. Is Earth the Solar System's only planet with both auroras and volcanos?

APOD: 2003 December 17 - A Proton Aurora
Explanation: What are auroras made out of? Triggered by solar activity, normal auroras are caused by collisions between fast-moving electrons and the oxygen and nitrogen in Earth's upper atmosphere. The electrons come from the magnetosphere, the region of space controlled by Earth's magnetic field. As the excited oxygen and nitrogen molecules return to their low energy state, they emit light, seen as the auroral glow. Sometimes, however, auroras can be caused by collisions with heavier protons, causing a more energetic display with strong ultraviolet emission. In addition, protons can temporarily capture an electron and emit light for themselves. Such a proton aurora is seen above, recorded by the IMAGE satellite. A special feature is the bright spot near picture center, embedded in a ring of auroral emission around the north magnetic pole of planet Earth. Most solar wind protons never reach the Earth to cause auroras because they are completely deflected away at a great distance by the Earth's magnetic field. The bright spot in the auroral ring indicates a particularly deep crack in the Earth's magnetic field where protons were able to flow along a temporarily connected region between the Sun and the Earth, relatively undeflected, until they impacted the Earth's ionosphere.

APOD: 2003 November 13 - Aurora Oklahoma
Explanation: Nestled in the central US, the state of Oklahoma is noted for its gorgeous prairie skies and wide-open spaces, but not for frequent visitations of the northern lights. Still, following the intense solar activity late last month, aurora did come sweeping down the Oklahoma plains and skywatcher Dave Ewoldt managed to catch up with this photogenic apparition 40 miles northwest of Oklahoma City at about 3am CST on October 29. Anticipating aurora sightings, Ewoldt had spent the evening photographing nighttime views of small towns in the area while keeping an eye toward the north. He reports, "I was just about ready to call it a night when the show started. When it did, it was like someone turned on a lightswitch. I wish it would have lasted longer... [it] seemed like it was completely done in about 25 minutes." Watery reflections of the colorful show highlight the foreground in the stunning image while stars of the Big Dipper and the northern sky shine behind the dazzling Oklahoma auroral display.

APOD: 2003 November 4 - Aurora Over Edmonton
Explanation: Northern and southern locales saw many a beautiful aurora over the last week, as particles from several large solar flares impacted the Earth. Many reported unusually red auroras, although colors across the spectrum were also seen. Power grids and orbiting satellites braced for the onslaught, but little lasting damage was reported. Pictured above, the Clover Bar Power Plant was photographed from the banks of the North Saskatchewan River in Edmonton, Alberta, Canada. A small pond in the foreground reflects predominantly green aurora light far in the distance. Two days ago, again unexpectedly, another large solar flare occurred from sunspot group 10486, the site of other recent major flares. This unusually active solar region is now rotating to the far side of the Sun.

APOD: 2003 October 30 - Aurora in Colorado Skies
Explanation: Vivid auroral displays were triggered by a cloud of high energy particles and magnetic fields from the Sun that collided with planet Earth's magnetosphere yesterday, October 29, at about 06:30 Universal Time. The collision was anticipated, following an intense solar flare and coronal mass ejection detected on October 28, and many anxious skywatchers were rewarded with an enjoyable light show. While aurorae don't normally haunt skies in the southern United States, they were reported from locations in Missouri, Texas, New Mexico, and California in the early morning hours. Near Yampa, Colorado astronomer Jimmy Westlake also spent early yesterday morning enjoying the stormy space weather. He was impressed by this colorful apparition of the northern lights -- produced by oxygen and nitrogen atoms excited by collisions with energetic particles from the magnetosphere and returning to lower energy states, at altitudes of 100 kilometers or more. Brighter stars shine through the extreme high-altitude glow which shows much lower clouds and the distant horizon in silhouette.

APOD: 2003 September 29 - Aurora Over the Chugach Mountains
Explanation: Auroras can make spectacular sights. Photographed above, flowing green auroras help the Moon illuminate the serene Portage Lake and the snowy Chugach Mountains near Anchorage, Alaska, USA. Although auroras might first appear to be moonlit clouds, they only add light to the sky and do not block background stars from view. Called northern lights in the northern hemisphere, auroras are caused by collisions between charged particles from the magnetosphere and air molecules high in the Earth's atmosphere. If viewed from space, auroras can be seen to glow in X-ray and ultraviolet light as well. Predictable auroras likely occur a few days after a powerful magnetic event has been seen on the Sun.

APOD: 2003 September 10 - Aurora Over Clouds
Explanation: Aurorae usually occur high above the clouds. The auroral glow is created when fast-moving charged particles from the Earth's magnetosphere impact air molecules high in the Earth's atmosphere. An oxygen molecule, for example, will emit a green light when reacquiring an electron lost during a collision. The lowest part of an aurora will typically occur at 100 kilometers and up, while most clouds usually exist only below about 10 kilometers. The relative heights of clouds and auroras are shown clearly in the above picture taken last month from near Quebec City, Canada. The most likely time to see an aurora is around midnight.

APOD: 2003 August 9 - A Perseid Aurora
Explanation: Just after the Moon set but before the Sun rose in the early morning hours of 2000 August 12, meteors pelted the Earth from the direction of the constellation Perseus, while ions pelted the Earth from the Sun. The meteors were expected as sub-sand grains long left behind by Comet Swift-Tuttle annually create the Perseids Meteor Shower. The aurorae were unexpected, however, as electrons, protons, and heavier ions raced out from a large Coronal Mass Ejection that had occurred just days before on the Sun. In the foreground is Hahn's Peak, an extinct volcano in Colorado, USA. The Perseid meteor shower peaks this year over the next few days, with as much as one bright meteor per minute visible from some locations.

APOD: 2003 July 2 - Aurora Over Cape Cod
Explanation: Active pillars of colorful aurora were captured dancing over a serenely smooth and nearly colorless Cape Cod Bay last month. North is straight ahead so that the town lights near the center originate from Provincetown, Massachusetts, USA. The unusual red colors in the aurora slightly reflect off the ocean inlet. Several familiar constellations are visible in the sky, including the famous stellar W of Cassiopeia on the far right.

APOD: 2003 April 8 - Aurora from Space
Explanation: What do auroras look like from space? From the ground, auroras dance high above clouds, frequently causing spectacular displays. The International Space Station (ISS) orbits just at the same height as many auroras, though. Therefore, sometimes it flies over them, but also sometimes it flies right through. The auroral electron and proton streams are too thin to be a danger to the ISS, just as clouds pose little danger to airplanes. ISS Science Officer Don Pettit captured a green aurora, pictured above in a digitally sharpened image. From orbit, Dr. Pettit reports, changing auroras can appear to crawl around like giant green amoebas. Far below, on planet Earth, the Manicouagan Impact Crater can be seen in northern Canada.

APOD: 2002 October 31 - Aurora in the Night
Explanation: For much of the month of October, traveling shock waves from the Sun and solar wind gusts have buffeted planet Earth's magnetosphere. As a result, skywatchers at high latitudes in the northern hemisphere were treated to many displays of the aurora borealis or northern lights. For example, on the first of October this particularly ghostly apparition was photographed looming above the horizon near the town of Inari in northern Finnish Lapland. But the solar wind is dying down for now. So if you just happen to be out tonight and you see such a specter haunting your skies ... it may not be an aurora. Have a safe and happy Halloween!

APOD: 2002 October 15 - Aurora's Ring
Explanation: Gusting solar winds and blasts of charged particles from the Sun made the early days of October rewarding ones for those anticipating auroras. While out enjoying the stormy space weather from Toemmeraas, Norway, Trygve Lindersen recorded this picturesque apparition of the northern lights with a digital camera on October 6. From this perspective, the curtains of green light formed a ring which seemed to hover, wraithlike, just above the foreground trees. But the ring of light was actually 100 kilometers or more above the trees and the greenish glow produced by oxygen molecules interacting with energetic electrons and fluorescing near the edge of space. After days of enchanting auroral displays on planet Earth, the solar activity which triggered October's geomagnetic storms seems to have subsided ... for now.

APOD: 2002 August 5 - Rays from an Unexpected Aurora
Explanation: This aurora was a bit of a surprise. For starters, last Friday morning, no intense auroral activity was expected at all. Possibly more surprising, however, the aurora appeared to show an usual structure of green rays from some locations. In the above image, captured from North Dakota, USA, a picket fence of green rays stretches toward the horizon. Mirroring the green rays is a red band, somewhat rare in its own right. Lights from the cities of Bismarck and Mandan are visible near the horizon. Large sunspot groups indicate that activity from the currently active Sun is relatively likely, possibly causing other streams of energetic particles to cascade onto the Earth and so causing more auroras.

APOD: 2002 April 22 - Comet and Aurora Over Alaska
Explanation: Can you spot the comet? Flowing across the frozen Alaskan landscape is an easily visible, colorful aurora. Just to the lower left, however, well in the background, is something harder to spot: Comet Ikeya-Zhang, the brightest comet of recent years. Although the aurora faded in minutes, the comet is just now beginning to fade. It remains just barely visible without aid, however, before sunrise in the East. The comet is actually a giant dirt-covered snowball that spends most of its time in the outer Solar System -- to where it is now returns. The above photograph was taken on March 20 when Comet Ikeya-Zhang was near its brightest. Careful inspection of the photo will uncover several other sky delights, including the giant galaxy M31.

APOD: 2002 March 20 - Aurora Over Antarctica
Explanation: Looking out from the bottom of the world, strange and spectacular sights are sometimes observed. Such was the case during the long Antarctic night of 1998, as awesome aurora sub-storms were photographed above scientific outposts. Visible in the left foreground of the above photograph is the Martin A. Pomerantz Observatory while the now defunct SPIREX telescope canvas dome is visible to its right. The outside temperature at the time this photograph was taken was about -73 Celsius (-100 Fahrenheit), although a slightly heated box sheltered the camera.

APOD: 2002 January 21 - Volcano and Aurora in Iceland
Explanation: Sometimes both heaven and Earth erupt. In Iceland in 1991, the volcano Hekla erupted at the same time that auroras were visible overhead. Hekla, one of the most famous volcanoes in the world, has erupted at least 20 times over the past millennium, sometimes causing great destruction. The last eruption occurred only two years ago but caused only minor damage. The green auroral band occurred fortuitously about 100 kilometers above the erupting lava. Is Earth the Solar System's only planet with both auroras and volcanos?

APOD: 2002 January 1 - The Secret of the Black Aurora
Explanation: What causes black aurora? These gaps in normal bright aurora are frequently recorded but rarely questioned. Recent research using data from four Cluster spacecraft orbiting the Earth has now likely found the secret: black auroras are actually anti-auroras. In normal auroras, electrons and/or predominantly negatively charged particles fall toward Earth along surfaces of constant magnetic field. They ionize the Earth's atmosphere on impact, causing the bright glows. In black anti-auroras, however, negatively charged particles are sucked out from the Earth's ionosphere along adjoining magnetic field lines. These dark anti-auroras can climb to over 20,000 kilometers and last for several minutes. Pictured above, a black aurora is seen dividing bright auroras over Fairbanks, Alaska, USA.

APOD: 2001 December 23 - Saturnian Aurora
Explanation: the second largest planet in the Solar System, Saturn's Rings are one of the most spectacular sights for earthbound telescopes. This image from the orbiting Hubble Space Telescope's STIS instrument, offers a striking view of another kind of ring around Saturn - pole encircling rings of ultraviolet aurora. Towering more than 1,000 miles above the cloud tops, these Saturnian auroral displays are analogous to Earth's. Energetic charged particles in the Solar Wind are funneled by the planet's magnetic field into polar regions where they interact with atmospheric gases. Following the ebb and flow of Saturn's aurora, researchers can remotely explore the planet's atmosphere and magnetic field. In this false color image, the dramatic red aurora identify emission from atomic hydrogen, while the more concentrated white areas are due to hydrogen molecules. In 2004, NASA plans to begin making close-up studies of the Saturnian system with the Cassini Spacecraft.

APOD: 2001 November 5 - Aurora Over Winnipeg
Explanation: What's happening above that city? The city is Winnipeg, Canada, and the phenomenon is aurora. These past few months have been active ones for our Sun, producing several coronal mass ejections (CMEs) of particles that have swept past our Earth and caused many spectacular auroras. Specifically in this case, a CME that occurred on October 9 impacted the Earth on October 11 and 12, causing nearly 12 hours of auroras. The above-pictured aurora had to be very bright to be seen over the lights of Winnipeg, the city well below and in front of the cascading atmospheric airglow. Lights reflecting off of a slight haze cause an unrelated glow that emanates from some of the buildings.

APOD: 2001 October 8 - A Yukon Aurora
Explanation: Last week was another good week for auroras. The story began about two weeks ago when two large Coronal Mass Ejections exploded off the Sun. Waves of elementary particles and ions swept out past the Earth on September 28 and 29, causing many auroras. A week ago, a flapping sheet that divides north and south regions of the Sun's magnetic field passed the Earth, again causing auroras. Pictured above is a particularly good image of one of the October 1 northern lights. Taken in Canada's Yukon, the city lights of Whitehorse are seen below dark clouds and a twisting green aurora.

APOD: 2001 April 6 - Aurora Over New Zealand
Explanation: Last weekend skygazers at middle and high latitudes around the globe were treated to expansive auroral displays as a magnetic storm raged around planet Earth. The storm was triggered by a solar coronal mass ejection associated with the giant sunspot group cataloged as active region number 9393. For example, pictured here in the early morning hours of April 1, the skies over New Zealand are alive with "southern lights". In the wide-angle time exposure, a towering red aurora is visible suspended above the foreground of a well lit lumber yard, train station, church steeple and buildings of the city of Dunedin. On April 2, the largest solar flare of the last 25 years also erupted near active region 9393, but because of its position near the Sun's edge the effects were largely directed away from our fair planet. However, all the recent solar activity underscores the fact that the solar maximum is still with us.

APOD: 2001 April 2 - Aurora Over Clouds
Explanation: Aurorae usually occur high above the clouds. The auroral glow is created when fast-moving particles ejected from the Sun impact air molecules high in the Earth's atmosphere. An oxygen molecule, for example, will glow in a green light when reacquiring an electron lost during a collision with a solar particle. The lowest part of an aurora will typically occur at 100 kilometers up, while most clouds usually exist only below about 10 kilometers. The relative heights of clouds and aurorae are shown clearly in the above picture from Iceland, where aurorae are relatively common. Over the past weekend, one of the largest sunspot groups ever recorded has been associated with explosive solar activity and expansive terrestrial aurora displays. Although in Earth's northern hemisphere aurorae are usually seen only in the far north, these aurorae were so prevalent they were imaged by a continuous nighttime camera operating in southern Arizona!

APOD: 2001 March 29 - Aurora Alaskan Style
Explanation: Have you checked the space weather report lately? With a coronal mass ejection (CME) headed our way and an immense sunspot group tracking across the solar photosphere, skygazers should be on the alert. The interaction of clouds of energetic particles from the active Sun with planet Earth's magnetosphere often produces significant geomagnetic storms and auroral displays. In fact, just days ago on March 24, photographer Jan Curtis pointed his camera straight up to captured this awesome auroral curtain towering in clear and very cold (-25F) skies over Fairbanks, Alaska, USA. Now, forecasts indicate that a recent Earth-directed CME may also trigger moderate geomagnetic storms over the next few days. Night sky aurora, possibly extending to middle latitudes, would be most likely on March 30-31.

APOD: 2001 February 10 - Aurora Astern
Explanation: Sailing upside down, 115 nautical miles above Earth, the crew of the Space Shuttle Endeavour made this spectacular time exposure of the southern aurora (aurora australis) in October of 1994. Aurora, also known as the northern and southern lights, appear as luminous bands or streamers of light which can extend to altitudes of 200 miles. They are typically visible from the Earth's surface at high latitudes and are triggered by high energy particles from the Sun. The delicate colors are caused by energetic electrons colliding with oxygen and nitrogen molecules in the upper atmosphere. In this picture, the rear structure of the shuttle Endeavour is in the foreground with the vertical tail fin pointed toward Earth. Star trails are the short streaks above Earth's horizon.

APOD: 2000 December 19 - A Close Up of Aurora on Jupiter
Explanation: Jupiter has aurorae. Like Earth, the magnetic field of the gas giant funnels charged particles released from the Sun onto the poles. As these particles strike the atmosphere, electrons are temporarily knocked away from existing gas molecules. Electric force attracts these electrons back. As the electrons recombine to remake neutral molecules, auroral light is emitted. In the above recently released photograph by the Hubble Space Telescope taken in ultraviolet light, the aurorae appear as annular sheets around the pole. Unlike Earth's aurorae, Jupiter's aurorae include several bright streaks and dots. These marks are caused by magnetic flux tubes connecting Jupiter to its largest moons. Specifically, Io caused the bright streak on the far left, Ganymede caused the bright dot below center, and Europa caused the dot to its right.

APOD: 2000 September 17 - Saturnian Aurora
Explanation: Girdling the second largest planet in the Solar System, Saturn's Rings are one of the most spectacular sights for earthbound telescopes. This image from the orbiting Hubble Space Telescope's STIS instrument, offers a striking view of another kind of ring around Saturn - pole encircling rings of ultraviolet aurora. Towering more than 1,000 miles above the cloud tops, these Saturnian auroral displays are analogous to Earth's. Energetic charged particles in the Solar Wind are funneled by the planet's magnetic field into polar regions where they interact with atmospheric gases. Following the ebb and flow of Saturn's aurora, researchers can remotely explore the planet's atmosphere and magnetic field. In this false color image, the dramatic red aurora identify emission from atomic hydrogen, while the more concentrated white areas are due to hydrogen molecules. In 2004, NASA plans to begin making close-up studies of the Saturnian system with the Cassini Spacecraft.

APOD: 2000 September 16 - X-Ray Earth
Explanation: Above is a picture of the Earth in x-rays, taken in March of 1996 from the orbiting Polar satellite. Most of the planet is dark with superposed continent and coordinate grids, while the bright x-ray emission near the north pole is shown in red. Why does the Earth have an x-ray glow? Actually, the Earth itself does not, but the aurora high in the Earth's atmosphere do glow with x-rays detectable by space-based instruments. Gusts of energetic ions from the Sun can distort the Earth's magnetosphere allowing high energy electrons spiraling along magnetic field lines to slam into the upper atmosphere above the magnetic poles. This activity causes shimmering visible aurora along with x-ray, ultraviolet, and radio emission. The x-rays are not dangerous to life on Earth because they are absorbed by the dense, lower atmosphere.

APOD: 2000 September 15 - Aurora In West Texas Skies
Explanation: The aurora borealis, or northern lights, are not a common sight in the southwestern United States. But a strong solar coronal mass ejection in early August triggered geomagnetic storms and aurora which were widely reported, even under west Texas skies. This striking view of the aurora was recorded from a site near El Paso, Texas and the Hueco Tanks State Historical Park at a latitude just shy of 32 degrees north. Polaris is the brightest star visible near the top and right of center while a Perseid meteor pierces the auroral glow left of picture center, below the bowl of the little dipper. Want to see an aurora? Dark skies and high latitudes (closer to the north or south poles) help. And you might keep an eye on the space weather report. The last big coronal mass ejection headed toward planet Earth was detected by space-based instruments on September 12. It may trigger geomagnetic storms and auroral activity beginning September 14th.

APOD: 2000 September 4 - Aurora Persei
Explanation: Last month, skywatchers were treated to an unexpected coincidence: bright aurorae occurred during the Perseid Meteor Shower. The above picture was taken August 12 and captures eerie looking aurorae and a faint Perseid meteor above Cross Lake in Wisconsin, USA. The near future holds promise for both more aurorae and a better meteor shower. Aurorae are becoming increasingly common as their trigger -- our Sun -- nears its period of highest activity during its eleven-year magnetic cycle. Coming up in mid-November is the quirky Leonids Meteor Shower. Although one of the better studied meteor showers, the Leonids have surprised astronomers many times and so many an optimistic skywatcher promises to be outside this year hoping for a memorable show.

APOD: 2000 August 21 - A Perseid Aurora
Explanation: Just after the Moon set but before the Sun rose in the early morning hours of August 12, meteors pelted the Earth from the direction of the constellation Perseus, while ions pelted the Earth from the Sun. The meteors were expected as sub-sand grains long left behind by Comet Swift-Tuttle annually create the Perseids Meteor Shower. The aurorae were unexpected, however, as electrons, protons, and heavier ions raced out from a large Coronal Mass Ejection that had occurred just days before on the Sun. In the foreground is Hahn's Peak, an extinct volcano in Colorado, USA.

APOD: 2000 May 19 - An Aurora Before the Storm
Explanation: Early April brought some of the most intense auroral storms this decade. An aurora on April 6 was reported to be the largest visible on Earth since 1989, and was seen throughout Europe and much of northern North America. On that day, many skywatchers expecting to see a rare alignment of planets were treated to a additional treat. Many reported aurorae with a relatively unusual red color. The above aurora recorded at dusk over Alaska sported the more typical green glow. A huge auroral ring can be seen superposed above trees and a building. Auroral activity occurs high in the Earth's atmosphere and is a direct result of storms on our Sun. As huge sheets of charged particles stream out from the Sun, a small fraction of these particles are funneled in by Earth's magnetic field and strike atoms high in the atmosphere, causing the sky to glow. The particles are harmless to people on Earth's surface, but can cause havoc on satellites in orbit far above.

APOD: 2000 April 10 - Aurora in Red and Yellow
Explanation: The past week brought some spectacular aurora to northern skies. These aurorae were caused by a large interplanetary shock wave that exploded from the Sun on April 4. When the shock wave reached the Earth on April 6, the resulting aurora could be seen in clear skies as far south as North Carolina. As the aurorae occurred high in the Earth's atmosphere, they were accompanied by an unusual alignment of planets far in the background. Pictured above that night, an unusual multicolored auroral display graced the skies above the domes of the Brno Observatory in the Czech Republic.

APOD: December 23, 1999 - Unusual Aurora During Solar Wind Dropout
Explanation: On May 10, for some unknown reason, the Solar Wind virtually stopped. Normally our Sun emits a wind of between five and ten energetic particles per cubic centimeter moving outward at about 500 kilometers per second. Late on May 10, however, this gale was reduced to a mere breeze of one particle per every five cubic centimeters. The Sun's Corona was suddenly able to flow out into the Solar System relatively unimpeded, creating beams of energetic electrons. One such beam apparently reached Earth's North Magnetic Pole, and was seen as the unusual X-ray aurora digitally reconstructed in the above false-color image. Our atmosphere absorbed the electrons. This display gave direct evidence, however, that Earth's North Magnetic Pole was connected to the Sun, while the Earth's South Magnetic Pole connected to the distant Solar System. The Solar Wind returned to normal on May 12.

APOD: November 2, 1999 - Aurora Through a Moonlit Sky
Explanation: A night sky can glow in fascinating ways. Through a clearing in the woods, the pictured sky above Alaska shines by reflected light from a nearby city, by the brightness of the Moon, and by aurora. The night sky in or near a city appears to contain relatively few stars because lights there reflect off atmospheric particles, hiding stars in a diffuse glow. The bright Moon also creates a diffuse sky glow, although much less bright than the analogous blue-sky glow created during the day by the Sun. Particles from the Sun crashing into the Earth's atmosphere are seen here as bands of aurora. These glows also illuminate visible clouds. Auroral displays are becoming more frequent as the Sun approaches Solar Maximum.

APOD: March 20, 1999 - Aurora and Orion
Explanation: Looking toward the south from low Earth orbit, the crew of the Space Shuttle Endeavor made this stunning time exposure of the Aurora Australis or southern lights in April of 1994. Aurora are visible at high northern latitudes as well, with the northern lights known as Aurora Borealis. They are caused by high energy electrons from the Solar Wind which are funneled into the atmosphere near the poles by the Earth's magnetic field. The reddish colors occur at the highest altitudes (about 200 miles) where the air is least dense. At lower altitudes and greater densities green tends to dominate ranging to a pinkish glow at the lowest. The familiar constellation of Orion the Hunter is clearly visible above the dark horizon in the background. Because of the shuttle's orbital motion, the bright stars in Orion appear slightly elongated.

APOD: January 23, 1999 - Saturnian Aurora
Explanation: Girdling the second largest planet in the Solar System, Saturn's Rings are one of the most spectacular sights for earthbound telescopes. This image from the orbiting Hubble Space Telescope's STIS instrument, offers a striking view of another kind of ring around Saturn - pole encircling rings of ultraviolet aurora. Towering more than 1,000 miles above the cloud tops, these Saturnian auroral displays are analogous to Earth's. Energetic charged particles in the Solar Wind are funneled by the planet's magnetic field into polar regions where they interact with atmospheric gases. Following the ebb and flow of Saturn's aurora, researchers can remotely explore the planet's atmosphere and magnetic field. In this false color image, the dramatic red aurora identify emission from atomic hydrogen, while the more concentrated white areas are due to hydrogen molecules. In 2004, NASA plans to begin making close-up studies of the Saturnian system with the Cassini Spacecraft.

APOD: November 11, 1998 - Aurora Above
Explanation: On some nights the sky is the most interesting show in town. This picture captures a particularly active and colorful display of aurora that occurred a month ago high above Alaska. Auroras are more commonly seen by observers located near the Earth's poles. Aurora light results from solar electrons and protons striking molecules high in the Earth's atmosphere. Planetary aurora activity can sometimes be predicted after particularly active solar coronal mass ejections.

APOD: October 21, 1998 - The Case of the Missing Aurora
Explanation: Sometimes, near midnight, auroras suddenly stop. Nobody knows why. This nightside gap in aurora was confirmed recently by D. Chua (U. Washington) and colleagues in data from the Ultraviolet Imager onboard the Polar spacecraft. The gap appears from space as a slight break in a more full auroral arc surrounding a magnetic pole of the Earth. Pictured above are clouds and auroras occurring last August near Wildcat Mountain in Wisconsin.

APOD: October 16, 1998 - Io Aurora
Explanation: Alluring aurora surrounding Io (eye-oh) appear as a ghostly glow while the volcanic moon orbits within Jupiter's dark shadow. Gas giant Jupiter is off to the right of this image, recorded in May by the robot Galileo spacecraft's solid state imaging camera from a distance of about 1.3 million kilometers. Energetic charged particles colliding with Io's atmospheric gases create the vivid colors and produce the red and green glow analogous to the aurora of Earth. The striking blue light is caused by dense volcanic plumes and may indicate regions electrically connected to Jupiter itself.

APOD: September 1, 1998 - A Colorful Aurora
Explanation: A solar storm overtook the Earth on August 26th. The Earth survived unscathed, as usual, although many northerners reported an impressive display of aurora. Many of these auroras changed rapidly, with patterns appearing and disappearing sometimes in less than a second. Out away from city lights, observers also reported an unusually spectacular array of colors. Some of these colors were captured in the photograph above. Solar particles that strike oxygen high in Earth's atmosphere cause rare, red auroras, while oxygen lower to the ground will glow a more familiar green. Ionized nitrogen glows blue or red.

APOD: May 5, 1998 - Aurora at Midnight
Explanation: What's happening behind those trees? Aurora. This picture was taken at midnight near Fairbanks, Alaska, and captures familiar trees, common clouds, and a glowing sky markedly different than a sunset. Particularly strange is the green auroral ring caused by ionized oxygen high in the Earth's atmosphere. The small water droplets composing clouds reflect and absorb aurora light, giving clouds a reddish tinge. The above picture was taken on September 20th of last year. In the next few years the Sun will reach the most active part of its 11 year cycle, meaning more puffs of high energy solar particles will be released, and more spectacular auroras will occur when these particles strike the Earth.

APOD: March 4, 1998 - Aurora Over Alaska
Explanation: Higher than the highest mountain, higher than the highest airplane, lies the realm of the aurora. Aurora rarely reach below 60 kilometers, and can range up to 1000 kilometers. Aurora light results from solar electrons and protons striking molecules in the Earth's atmosphere. Frequently, when viewed from space, a complete aurora will appear as a circle around one of the Earth's magnetic poles. The above photograph was taken in January in Alaska and shows a spectacular aurora borealis above a frozen landscape which includes spruce trees and the photographer's truck. The picture had to be taken quickly as the temperature was below -40 degrees.

APOD: February 22, 1998 - Southern Lights and Shuttle Glow
Explanation: A background of distant stars, sinuous and spiky bands of Southern Lights (Aurora Australis), and the faint glow of charged plasma (ionized atomic gas) surrounding the Space Shuttle Discovery's engines give this photo from the STS-39 mission an eerie, otherworldly look. This image reflects Discovery's April 1991 mission well - its payload bay (PLB) was filled with instruments designed to study celestial objects, aurora and atmospheric phenomena, and the low Earth orbit environment around the PLB itself. The aurora seen here are at a height of about 50-80 miles. Aurora are caused by charged particles in the solar wind, channeled through the Earth's magnetic field which excite molecules in the upper atmosphere.

APOD: January 23, 1998 - Jovian Aurora
Explanation: These two recently released Hubble Space Telescope close-ups show the Northern and Southern lights ... on Jupiter. Like aurora on Earth, these Jovian aurora are caused by charged particles funneled into the atmosphere above the planet's North (right) and South poles by magnetic fields. But Jupiter's magnetic field is extremely large and ionized material expelled from the volcanic moon Io is trapped in it creating light shows 1,000 times more intense than Earth's auroral storms. Charged particles released by Io are also funneled along magnetic flux tubes which form a direct "bridge" to the Jovian atmosphere. The result is auroral hot spots - magnetic footprints 600 or more miles across which race over Jupiter's cloud tops. A hot spot is visible in both images as a comet-like feature just outside the polar auroral rings. In these false color ultraviolet images, Jupiter's limb (edge) appears dull brown while the auroral displays are shades of white and blue.

APOD: January 9, 1998 - Saturnian Aurora
Explanation: Girdling the second largest planet in the Solar System, Saturn's Rings are one of the most spectacular sights for earthbound telescopes. This recently released image, from the orbiting Hubble Space Telescope's STIS instrument, offers a striking view of another kind of ring around Saturn - pole encircling rings of ultraviolet aurora. Towering more than 1,000 miles above the cloud tops, these Saturnian auroral displays are analogous to Earth's. Energetic charged particles in the Solar Wind are funneled by the planet's magnetic field into polar regions where they interact with atmospheric gases. Following the ebb and flow of Saturn's aurora, researchers can remotely explore the planet's atmosphere and magnetic field. In this false color image, the dramatic red aurora identify emission from atomic hydrogen, while the more concentrated white areas are due to hydrogen molecules. In 2004, NASA plans to begin making close-up studies of the Saturnian system with the Cassini Spacecraft.

APOD: April 18, 1997 - Solar Storm Causes X-Ray Aurora
Explanation: On April 7, the SOHO spacecraft spotted a Solar Storm ejecting a cloud of energetic particles toward planet Earth. The plasma cloud's center missed Earth, but high energy particles swept up by Earth's magnetosphere still created a geomagnetic storm! Residents of northerly lattitudes were treated to the spectacle of brilliant aurora as curtains of green and white light danced across the sky. In this image from April 11, the Polar Ionospheric X-ray Imaging Experiment (PIXIE) onboard NASA's orbiting POLAR spacecraft records the strongest X-ray aurora seen in more than a year of operation. The false color image overlaying a map of North America reveals X-rays generated in the upper atmosphere by showers of high energy electrons.

APOD: April 2, 1997 - A Complete Aurora
Explanation: Aurora frequently make complete rings around a pole of the Earth. This particular "crown", visible in orange near the top of this image, was taken by the orbiting Polar spacecraft about one year ago and released by NASA last month. A complete auroral oval is normally hard to photograph because part of it usually occurs over a brightly sunlit portion of the Earth. Polar's Earth Camera, however, can be programmed to filter out all but a certain type of ultraviolet light. In this "color", atmospheric oxygen can glow brighter than reflected sunlight. People with normal eyesight living near the Great Lakes in North America would have been able to see this aurora, were it not daytime!

APOD: January 26, 1997 - Aurora and Orion
Explanation: Looking toward the south from low Earth orbit, the crew of the Space Shuttle Endeavor made this stunning time exposure of the Aurora Australis or southern lights in April of 1994. Aurora are visible at high northern latitudes as well, with the northern lights known as Aurora Borealis. They are caused by high energy electrons from the Solar Wind which are funneled into the atmosphere near the poles by the Earth's magnetic field. The reddish colors occur at the highest altitudes (about 200 miles) where the air is least dense. At lower altitudes and greater densities green tends to dominate ranging to a pinkish glow at the lowest. The familiar constellation of Orion the Hunter is clearly visible above the dark horizon in the background. Because of the shuttle's orbital motion, the bright stars in Orion appear slightly elongated.

APOD: January 1, 1997 - Aurora Over Circle, Alaska
Explanation: Aurora can make spectacular sights. This particular aurora was photographed hovering over the town of Circle, Alaska. Although Aurora might first appear to be moonlit clouds, they only add light to the sky, and hence can not block background stars from view. Called "northern lights" in the northern hemisphere of the Earth, aurora are caused by charged particles streaming from the Sun entering the Earth's atmosphere. If viewed from space, aurora glow in X-ray light as well as in the visible! Several WWW sites can tell you if aurora are predicted to be visible in your area.

APOD: November 30, 1996 - Aurora Astern
Explanation: Sailing upside down, 115 nautical miles above Earth, the crew of the Space Shuttle Endeavour made this spectacular time exposure of the southern aurora (aurora australis) in October of 1994. The aurora, also known as the northern and southern lights, appear as luminous bands or streamers of light which can extend to altitudes of 200 miles. They are typically visible from the Earth's surface at high latitudes and are caused by high energy particles from the Sun. The delicate colors are caused by energetic electrons colliding with oxygen and nitrogen in the atmosphere. In this picture, the rear structure of the Space Shuttle is visible in the foreground with the vertical tail fin pointed toward Earth. Star trails are visible as small streaks above Earth's horizon.

APOD: June 19, 1996 - Aurora: Curtains in the Sky
Explanation: Looking out over Lake Superior at dusk you see Venus (lower left) and ... curtains? Like an ant looking up at window curtains, aurora frequently appear as huge flowing light displays. These colorful, often spectacular phenomena are most frequently visible from locations near the Earth's poles. Aurora are caused by electrons from the solar wind funneling to Earth along magnetic field lines, and striking atoms and molecules in our atmosphere. Auroral color is determined by which atmospheric ions are struck and recombine to form neutral atoms. Hourly updates of auroral sightings are posted to the WWW. It is still controversial whether aurora make any sound audible from the ground. If you think you have "heard an aurora," please report it!

APOD: May 27, 1996 - Aurora Crown the Earth
Explanation: What do aurora look like from space? The POLAR spacecraft answered this by photographing an auroral oval surrounding the north pole of the Earth, causing displays on both the night and day side. The auroral sub-storm, pictured in false-color above, developed within 15 minutes and may have lasted as long as on hour. Aurora are caused by charged particles streaming away from the Sun and towards the Earth. As the particles fall to Earth, they spiral along magnetic field lines and cause colorful radiation. The UVI experiment onboard the POLAR spacecraft is equipped with special filters that allow it to see aurora in a band of ultraviolet light where sunlight is relatively dim. The more red the emission depicted in the above photo, the more intense the radiation. Earth's continents have been drawn in for clarity

APOD: May 6, 1996 - Southern Lights and Shuttle Glow
Explanation: A background of distant stars, sinuous and spiky bands of Southern Lights (Aurora Australis), and the faint glow of charged plasma (ionized atomic gas) surrounding the Space Shuttle Discovery's engines give this photo from the STS-39 mission an eerie, otherworldly look. This image reflects Discovery's April 1991 mission well - its payload bay (PLB) was filled with instruments designed to study celestial objects, aurora and atmospheric phenomena, and the low Earth orbit environment around the PLB itself. The aurora seen here are at a height of about 50-80 miles and caused by charged particles in the solar wind, channeled through the van Allen Radiation Belts which excite atoms of oxygen in the upper atmosphere.

APOD: November 14, 1995 - Aurora and Orion
Explanation: Looking toward the south from low Earth orbit, the crew of the Space Shuttle Endeavor made this stunning time exposure of the Aurora Australis (southern lights) in April of 1994. The aurora are caused by high energy electrons from the Solar Wind which are funneled into the atmosphere by the Earth's magnetic field. The reddish colors occur at the highest altitudes (about 200 miles) where the air is least dense. At lower altitudes and greater densities green tends to dominate. At the lowest altitudes a pinkish glow is sometimes produced. The familiar constellation of Orion the Hunter is clearly visible above the dark horizon in the background. Because of the shuttle's orbital motion, the bright stars in Orion appear slightly elongated.

APOD: October 26, 1995 - Aurora Astern
Explanation: Sailing upside down, 115 nautical miles above Earth, the crew of the Space Shuttle Endeavour made this spectacular time exposure of the southern aurora (aurora australis) in October of 1994. The aurora, also known as the northern and southern lights, appear as luminous bands or streamers of light which can extend to altitudes of 200 miles. They are typically visible from the Earth's surface at high latitudes and are caused by high energy particles from the Sun. The delicate colors are caused by energetic electrons colliding with oxygen and nitrogen in the atmosphere. In this picture, the rear structure of the Space Shuttle is visible in the foreground with the vertical tail fin pointed toward Earth. Star trails are visible as small streaks above Earth's horizon.