Astronomy Picture of the Day |
APOD: 2023 April 30 – Saturn's Moon Helene in Color
Explanation:
Although its colors may be subtle, Saturn's moon Helene is an enigma in any light.
The moon was imaged in
unprecedented detail in 2012 as the
robotic Cassini spacecraft orbiting Saturn
swooped
to within a single Earth diameter of the
diminutive moon.
Although conventional craters and hills
appear, the
above
image also
shows terrain that appears unusually smooth and streaked.
Planetary astronomers are inspecting these detailed images of
Helene to
glean clues
about the origin and evolution of the 30-km across floating iceberg.
Helene is also unusual because it circles
Saturn just ahead of the large moon
Dione, making it one of only
four known
Saturnian moons to occupy a gravitational dimple known as a stable
Lagrange point.
APOD: 2021 April 4 - In, Through, and Beyond Saturn's Rings
Explanation:
Four moons are visible on the
featured image -- can you find them all?
First -- and farthest in the background -- is
Titan, the largest moon of
Saturn and one of the larger moons in the
Solar System.
The dark feature across the top of this perpetually cloudy world is the
north polar hood.
The next most obvious moon is bright
Dione,
visible in the foreground, complete with craters and long
ice cliffs.
Jutting in from the left are several of Saturn's
expansive rings,
including Saturn's A ring featuring the dark
Encke Gap.
On the far right, just outside the rings, is
Pandora,
a moon only 80-kilometers across that
helps shepherd
Saturn's F ring.
The fourth moon?
If you look closely inside Saturn's rings, in the
Encke Gap,
you will find a speck that is actually
Pan.
Although one of Saturn's smallest moons at 35-kilometers across,
Pan is massive enough to help keep the
Encke gap relatively free of ring particles.
After more than a decade of exploration and discovery, the
Cassini spacecraft ran
low on fuel in 2017 and was directed to
enter Saturn's atmosphere,
where it surely
melted.
APOD: 2019 December 29 - Cassini Spacecraft Crosses Saturn's Ring Plane
Explanation:
If this is Saturn, where are the rings?
When Saturn's "appendages"
disappeared in 1612,
Galileo
did not understand why.
Later that century, it became understood that
Saturn's
unusual protrusions were rings and that when the
Earth crosses the ring plane,
the edge-on rings will
appear to disappear.
This is because Saturn's rings are confined to a plane many times thinner, in proportion, than a
razor blade.
In modern times, the
robot Cassini spacecraft orbiting Saturn frequently crossed
Saturn's ring plane during its mission to Saturn,
from 2004 to 2017.
A series of plane crossing images from 2005 February
was dug out of the vast
online Cassini raw image archive by interested Spanish amateur
Fernando Garcia Navarro.
Pictured here, digitally cropped and set in representative colors,
is the striking result.
Saturn's thin ring plane
appears in blue, bands and clouds in
Saturn's upper atmosphere
appear in gold.
Details of Saturn's rings can be seen in the high
dark shadows across the top of this image,
taken back in 2005.
The moons
Dione and
Enceladus appear as
bumps in the rings.
APOD: 2019 June 15 - Stereo Helene
Explanation:
Get out your
red/blue glasses and float next to Helene,
small, icy moon of Saturn.
Appropriately named, Helene
is one of four known Trojan moons, so called because it orbits at a
Lagrange
point.
A Lagrange point is a gravitationally stable position
near two massive bodies, in this case
Saturn
and larger moon Dione.
In fact, irregularly shaped ( about 36 by 32 by 30 kilometers)
Helene orbits at Dione's leading Lagrange point while
brotherly ice moon Polydeuces follows at Dione's trailing Lagrange
point.
The sharp stereo
anaglyph was constructed from two
Cassini images captured during
a
close flyby in 2011.
It shows part of the Saturn-facing hemisphere of Helene
mottled with craters and gully-like features.
APOD: 2015 August 24 - Dione, Rings, Shadows, Saturn
Explanation:
What's happening in this strange juxtaposition of moon and planet?
First and foremost, Saturn's moon Dione was
captured here
in a dramatic panorama by the robotic
Cassini spacecraft currently orbiting the giant planet.
The bright and
cratered moon itself spans about 1100-km, with the large multi-ringed
crater Evander visible on the lower right.
Since the rings of Saturn are seen here nearly edge-on, they are
directly visible only as a thin horizontal line that passes behind
Dione.
Arcing across the bottom of
the image, however, are
shadows of Saturn's rings, showing some of the rich texture that could not be seen directly.
In the background, few cloud features are visible on
Saturn.
The featured image was taken during the
last planned flyby of Dione by Cassini, as the spacecraft is scheduled to
dive into Saturn's atmosphere
during 2017.
APOD: 2015 July 8 - In the Company of Dione
Explanation:
That is not our Moon.
It's Dione,
and it’s a moon of Saturn.
The robotic Cassini spacecraft
took the
featured image during a flyby of Saturn's cratered Moon last month.
Perhaps what makes
this image so interesting, though, is the background.
First, the large orb looming behind
Dione is Saturn itself,
faintly lit by sunlight first reflected from the rings.
Next, the thin lines running diagonally across the image are the
rings of Saturn themselves.
The millions of icy rocks that
compose Saturn's spectacular rings all orbit Saturn in the same
plane, and so appear surprisingly thin when seen nearly edge-on.
Front and center,
Dione appears in
crescent phase, partially lit by the Sun that is off to the lower left.
A careful inspection of the ring plane should also locate the moon
Enceladus on the upper right.
APOD: 2015 June 3 - Flyby Image of Saturn's Sponge Moon Hyperion
Explanation:
Why does this moon look like a sponge?
To better investigate,
NASA and
ESA sent the Saturn-orbiting robotic
spacecraft Cassini zooming past
Saturn's moon
Hyperion, once again, earlier this week.
One of the images beamed back to Earth is
featured above, raw and unprocessed.
Visible, as expected, are many
unusually shaped craters with an unusual dark material at the bottom.
Although Hyperion
spans about 250 kilometers, its small gravitational tug on
Cassini indicates that it is mostly empty space and so has very low
surface gravity.
Therefore, the
odd shapes of many of Hyperion's craters are thought to result from impacts that
primarily compress and eject surface material -- instead of the more
typical round craters that appear after a circular shock wave that explosively redistributes surface material.
Cassini is
on track for another flyby of
Saturn's
Dione in about two weeks.
APOD: 2014 November 7 - The Map of Dione
Explanation:
This cylindrical projection global map is
one
of six new color maps
of Saturn's midsized icy moons,
constructed using 10 years of image data from the
Cassini spacecraft.
Discovered by Cassini (the astronomer) in 1684,
Dione is about 1,120 kilometers across.
Based on data extending
from infrared to ultraviolet,
the full resolution of this latest space-age map is 250 meters per pixel.
The remarkable brightness difference between the
tidally locked
moon's lighter leading hemisphere (right) and
darker trailing hemisphere clearly stands out.
Like other Saturn moons orbiting within the broad E-ring, Dione's
leading hemisphere is kept shiny as it picks up a coating of
the faint ring's icy material.
The E-ring material is
constantly replenished by
geysers on moon
Enceladus' south pole.
Lighter, younger surface fractures
also appear to cross the dark, cratered trailing hemisphere.
APOD: 2013 March 29 - Ringside with Rhea
Explanation:
Orbiting in the plane of Saturn's rings,
Saturnian moons have a perpetual
ringside view of the gas giant planet.
Of course, while passing near the ring plane
the Cassini spacecraft also shares
their stunning perspective.
The thin rings themselves slice across the middle of
this Cassini snapshot from April 2011.
The scene looks toward the dark
night side of Saturn, in the frame at the
left, and the still sunlit side of the rings from just above the
ringplane.
Centered, over 1,500 kilometers across, Rhea is
Saturn's second largest moon and
is closest to the spacecraft, around 2.2 million kilometers away.
To Rhea's right, shiny, 500 kilometer diameter
Enceladus is about 3 million kilometers distant.
Dione, 1,100 kilometers wide,
is 3.1 million kilometers from Cassini's camera
on the left, partly blocked by Saturn's night side.
APOD: 2013 January 5 - Stereo Helene
Explanation:
Get out your
red/blue glasses and float next to Helene,
small, icy moon of Saturn.
Appropriately named, Helene
is one of four known Trojan
moons, so called because it orbits at a
Lagrange
point.
A Lagrange point is a gravitationally stable position
near two massive bodies, in this case
Saturn and larger moon Dione.
In fact, irregularly shaped ( about 36 by 32 by 30 kilometers)
Helene orbits at Dione's leading Lagrange point while
brotherly ice moon Polydeuces follows at Dione's trailing Lagrange
point.
The sharp stereo
anaglyph
was constructed from two
Cassini images
(N00172886,
N00172892) captured during
a close flyby in 2011.
It shows part of the Saturn-facing hemisphere of Helene
mottled with craters and gully-like features.
APOD: 2012 November 5 - Saturn's Moon Dione in Slight Color
Explanation:
Why does one half of Dione have more craters than the other?
Start with the fact that
Saturn's moon Dione
has one side that always faces Saturn, and one side that always faces away.
This is similar to
Earth's Moon.
This tidal locking
means that one side of
Dione always leads as the moon progresses in its orbit,
while the other side always trails.
Dione
should therefore have undergone a significant number of impacts on its leading half.
Strangely, the current leading half of
Dione
is less cratered than the trailing half.
A leading explanation is that some crater-forming impacts were so large they spun
Dione,
changing the part that suffered the highest impact rate before the
moon's spin again became locked.
The above detailed image of Dione highlighting the moon's subtle hues
is a meticulously-constructed mosaic --
by an dedicated amateur --
of pictures taken during the April 2010
flyby of Dione by NASA's robotic
Cassini spacecraft.
APOD: 2012 May 21 - A Close Pass of Saturn's Moon Dione
Explanation:
What's that past Dione?
When making its closest pass yet of Saturn's moon
Dione
late last year, the robotic Cassini spacecraft snapped this far-ranging picture featuring Dione, Saturn's rings, and the two small moons
Epimetheus and
Prometheus.
The above image
captures part of the heavily cratered snow-white surface of the 1,100 kilometer wide
Dione, the thinness of Saturn's rings, and the
comparative darkness
of the smaller moon Epimetheus.
The image was taken when Cassini was only about 100,000 kilometers from the
large icy moon.
Future events in Cassini's
continuing exploration of Saturn and its moons include tomorrow's
flyby of Titan
and imaging the distant Earth
passing behind Saturn in June.
APOD: 2012 May 2 - Saturn's Moon Helene in Color
Explanation:
Although its colors may be subtle, Saturn's moon Helene is an enigma in any light.
The moon was imaged in
unprecedented detail last June as the
robotic
Cassini spacecraft orbiting Saturn
swooped
to within a single Earth diameter of the
diminutive moon.
Although conventional craters and hills
appear, the
above
image also
shows terrain that appears unusually smooth and streaked.
Planetary astronomers are inspecting these detailed images of
Helene to glean
clues
about the origin and evolution of the 30-km across floating iceberg.
Helene is also unusual because it circles
Saturn just ahead of the large moon
Dione, making it one of only
four known Saturnian moons to occupy a gravitational well known as a stable
Lagrange point.
APOD: 2012 April 14 - Six Moons of Saturn
Explanation:
How many moons does Saturn have?
So far 62 have
been discovered, the smallest only a fraction
of a kilometer across.
Six of its largest satellites can be seen here, though, in a sharp
Saturnian family portrait
taken on March 9.
Larger than Earth's Moon and even slightly larger than Mercury,
Titan
has a diameter of 5,150 kilometers and starts the line-up
at the lower left.
Continuing to the right across the frame are
Mimas,
Tethys, [Saturn],
Enceladus,
Dione, and
Rhea at far right.
Saturn's first known natural satellite, Titan was
discovered in 1655 by
Dutch astronomer Christiaan Huygens, while most recently the
satellite provisionally designated
S/2009 S1 was found
by the Cassini Imaging Science Team in 2009.
Tonight,
Saturn reaches opposition
in planet Earth's sky, offering
the best telescopic views of the ringed planet and moons.
APOD: 2012 January 5 - Ringside with Titan and Dione
Explanation:
Orbiting in the plane of
Saturn's rings,
Saturnian moons have a perpetual ringside view of the
gorgeous gas giant planet.
Of course, while passing near the ring plane
the Cassini spacecraft also shares
their stunning
perspective.
The rings themselves can be seen slicing across the middle of
this Cassini snapshot from May of last year.
The scene features Titan, largest,
and Dione,
third largest moon of Saturn.
Remarkably thin,
the bright rings still cast arcing shadows
across the planet's cloud tops at the bottom of the frame.
Pale
Dione is about 1,100 kilometers
across and orbits over 300,000 kilometers from the
visible outer edge of the A ring.
Dione is seen through Titan's
atmospheric haze.
At 5,150 kilometers across, Titan is about 2.3 million kilometers from
Cassini, while Dione is 3.2 million kilometers away.
APOD: 2011 October 26 - In, Through, and Beyond Saturn's Rings
Explanation:
A fourth moon is visible on the
above image
if you look hard enough.
First -- and farthest in the background -- is
Titan, the largest moon of Saturn and one of the larger moons in the Solar System.
The dark feature across the top of this perpetually cloudy world is the
north polar hood.
The next most obvious moon is bright
Dione,
visible in the foreground, complete with craters and long
ice cliffs.
Jutting in from the left are several of Saturn's
expansive rings,
including Saturn's A ring featuring the dark
Encke Gap.
On the far right, just outside the rings, is
Pandora,
a moon only 80-kilometers across that
helps shepherd
Saturn's F ring.
The fourth moon?
If you look closely in the Encke Gap you'll find a speck that is actually
Pan.
Although one of Saturn's smallest moons at 35-kilometers across, Pan is massive enough to help keep the
Encke gap relatively free of ring particles.
APOD: 2011 June 23 - Stereo Helene
Explanation:
Get out your
red/blue glasses and float next to Helene,
small, icy moon of Saturn.
Appropriately named, Helene
is one of four known Trojan
moons, so called because it orbits at a
Lagrange point.
A Lagrange point is a gravitationally stable position
near two massive bodies, in this case
Saturn and larger moon Dione.
In fact, irregularly shaped ( about 36 by 32 by 30 kilometers)
Helene orbits at Dione's leading Lagrange point while
brotherly ice moon Polydeuces follows at Dione's trailing Lagrange
point.
The sharp stereo anaglyph
was constructed from two
Cassini images
(N00172886,
N00172892) captured during
the recent close flyby.
It shows part of the Saturn-facing hemisphere of Helene
mottled with craters and gully-like features.
APOD: 2010 April 20 - Saturn's Moons Dione and Titan from Cassini
Explanation:
What would it be like to see a sky with many moons?
Such is the sky above
Saturn.
When appearing close to each other, moons will show a similar
phase.
A view with two of the more famous moons of
Saturn in gibbous
phase was captured last month by the
robot spacecraft
Cassini now orbiting Saturn.
Titan,
on the left, is among the largest moons in the
Solar System and is perpetually shrouded in clouds.
In 2005, the Huygens probe
landed on Titan
and gave humanity its first view of its unusual surface.
Dione,
on the right, has less than a quarter of
Titan's diameter and has no
significant atmosphere.
The above uncalibrated
image
was taken on April 10 after
Cassini
swooped by each moon the previous week.
APOD: 2010 April 5 - Prometheus Remastered
Explanation:
What does Saturn's shepherd moon Prometheus really look like?
The raw images from the
robotic Cassini spacecraft's January flyby of the small moon showed tantalizing clues on
grainy images,
but now that the
Cassini team has
digitally remastered these images,
many more details have come out.
Pictured above, Prometheus more clearly shows its oblong shape as well as numerous craters over its 100-kilometer length.
In the above image, the bright part of
Prometheus is lit directly by the Sun,
while much of the dark part is
still discernible through sunlight first reflected off of
Saturn.
These new surface details, together with
the moon's
high reflectivity, can now help humanity better understand the history of
Prometheus
and Saturn's rings.
Today, Cassini has a
planned targeted flyby of Saturn's largest moon
Titan, while on Wednesday,
Cassini is scheduled to swoop to within 600 kilometers of
Dione.
APOD: 2010 March 10 - Saturn's Moon Helene from Cassini
Explanation:
What's happening on the surface of Saturn's moon Helene?
The moon was imaged in
unprecedented detail last week as the
robotic
Cassini spacecraft orbiting Saturn
swooped to
within
two Earth diameters of the diminutive moon.
Although conventional craters and hills appear, the above raw and unprocessed image also
shows terrain that appears unusually smooth and
streaked.
Planetary astronomers will be inspecting these detailed images of
Helene to glean clues about the origin and evolution of the 30-km across floating iceberg.
Helene is also unusual because it circles Saturn just ahead of the large moon
Dione, making it one of only four known Saturnian moons to occupy a gravitational well known as a stable
Lagrange point.
APOD: 2009 March 19 - Saturn: Moons in Transit
Explanation:
Every 14 to 15 years, Saturn's rings
are tilted
edge-on to our line of sight.
As the bright, beautiful rings seem to grow narrower
it becomes increasingly
difficult to see them, even with large telescopes.
But it does provide the opportunity to watch multiple
transits of Saturn's moons.
During a transit, a sunlit moon and its shadow
glide across the cloudy face of the gas giant.
Recorded on February 24,
this
Hubble image is part of a
sequence
showing the transit of four of Saturn's moons.
From left to right are Enceladus
and shadow,
Dione
and shadow, and
Saturn's largest moon Titan.
Small moon Mimas is just
touching Saturn's disk near the
ring plane at the far right.
The shadows of Titan and Mimas have both moved off
the right side of the disk.
Saturn itself
has an equatorial diameter of about 120,000 kilometers.
APOD: 2007 August 1- Unusual Cratering on Saturns Dione
Explanation:
Why does one half of Dione have more craters than the other?
Start with the fact that
Saturn's moon Dione
always has one side that faces Saturn, and always has one side that faces away.
This is similar to
Earth's Moon.
This tidal locking
means that one side of
Dione always leads as the moon progresses in its orbit,
while the other side always trails.
Dione
should therefore have undergone a significant amount of impacts on its leading half.
But the current leading half of
Dione
is less cratered than the trailing half!
A possible explanation is that some impacts were so large they spun
Dione,
sometimes changing the part that suffered the highest impact rate before the
moon's spin again became locked.
Pictured above,
it is the top part of Dione that appears significantly more cratered than the bottom half.
APOD: 2006 September 5 - Bright Cliffs Across Saturns Moon Dione
Explanation:
What causes the bright streaks on Dione?
Recent images of this unusual moon by the
robot Cassini spacecraft now orbiting
Saturn
are helping to crack the mystery.
Close inspection of Dione's trailing hemisphere,
pictured above, indicates that the white wisps are composed of deep
ice cliffs dropping hundreds of meters.
The cliffs may indicate that Dione has undergone some sort of
tectonic surface displacements in its past.
The bright ice-cliffs run across some of
Dione's many craters, indicating that the
process that created them occurred later than the
impacts that created those craters.
Dione
is made of mostly water ice but its relatively high density
indicates that it contains much
rock inside.
Giovanni Cassini discovered Dione in 1684.
The above image was taken at the end of July from a distance of about 263,000 kilometers.
Other high resolution images of
Dione were taken by the passing
Voyager spacecraft in 1980.
APOD: 2005 December 31 - A Year at Saturn
Explanation:
Arriving at Saturn in July of 2004, the
Cassini spacecraft
has now spent a year and a half exploring the
magnificent rings and moons of the distant gas giant.
The year 2005 began with Cassini's
Huygens probe landing
on Saturn's large moon Titan.
Cassini's continuing series of close flybys
also revealed
details and discoveries
across the surface of the smog shrouded moon.
In fact, with a ringside
seat throughout 2005, Cassini's cameras
have made spectacular pictures of Titan along with
Saturn's
other moons and rings
almost
common place.
But often, Saturn itself provided the most dramatic backdrop.
In this
view, Saturn's moon Dione lies in front of edge-on
rings and the gas giant's cloud tops draped with broad
ring shadows.
Dione is 1,118 kilometers across
and lies about 300,000 kilometers from the ring's edge.
APOD: 2005 October 26 - 4500 Kilometers Above Dione
Explanation:
What does the surface of Saturn's moon Dione look like?
To find out, the
robot Cassini spacecraft
currently orbiting
Saturn
flew right past the fourth largest moon of the giant planet earlier this month.
Pictured above
is an image taken about 4,500 kilometers above
Dione's icy surface,
spanning about 23 kilometers.
Fractures, grooves, and craters in
Dione's ice and rock are visible.
In many cases, surface features are caused by unknown processes and can only be described.
Many of the
craters have bright walls but
dark floors, indicating that fresher ice is brighter.
Nearly parallel grooves run from the upper right to the lower left.
Fractures sometimes across the bottom of craters, indicating a relatively recent formation.
The lip of a 60-kilometer wide crater runs from the middle left to the upper
center of the image, while the crater's center is visible on the lower right.
Images like this
will continue to be
studied to better understand
Dione as well as
Saturn's complex system of
rings and
moons.
APOD: 2005 October 21 - Ringside
Explanation:
Orbiting in the plane of
Saturn's rings,
Dione and the other icy saturnian moons have a perpetual
ringside view of the
gorgeous gas giant
planet.
Of course, while passing through the ring plane
the Cassini spacecraft also shares
their stunning
perspective.
The rings themselves can be seen slicing across the bottom of
this Cassini snapshot.
Remarkably thin,
the bright rings still cast arcing shadows
across the planet's cloud tops.
Pale
Dione, in the foreground, is
about 1,100 kilometers
across and orbits over 300,000 kilometers from the
visible outer edge of the A ring.
APOD: 2005 March 29 - Crescents of Titan and Dione
Explanation:
What would it be like to see a sky with many moons?
Such is the sky above
Saturn.
When appearing close to each other, moons will show a similar
phase.
A view with two of the more famous moons of
Saturn in crescent
phase was captured last month by the
robot spacecraft
Cassini now orbiting Saturn.
Titan,
on the lower left, is among the largest moons in the
Solar System and is perpetually shrouded in clouds.
Recently, the Huygens probe
landed on Titan
and gave humanity its first view of its unusual surface.
Dione,
on the upper right, has less than a quarter of
Titan's
diameter and has no significant atmosphere.
Dione,
although appearing smaller, was only half the distance to
Titan when the
above image was taken.
APOD: 2005 February 15 - Saturns Moon Rhea from Cassini
Explanation:
Each moon of Saturn seems to come with its own
mystery.
Rhea, Saturn's second largest moon behind
Titan, shows unusual wisps, visible above as light colored streaks.
Higher resolution images of similar wisps on Dione indicate that they
might be made of long braided fractures.
Rhea is composed mostly of
water ice,
but likely has a
small rocky core.
Rhea's rotation and orbit are locked together, just like
Earth's Moon, so that one
side always faces Saturn.
A consequence of this is that one side always leads the other.
Rhea's leading surface is much more heavily
cratered than the trailing surface, pictured above.
The above image in natural color was taken last month by the
Cassini robot spacecraft in orbit around Saturn.
APOD: 2004 December 1 - Saturn's Moon Dione from Cassini
Explanation:
What causes the bright streaks on Dione?
Recent and likely future images of this unusual moon by the
robot Cassini spacecraft now orbiting
Saturn
might help us find out.
The above image was taken at the end of October from a distance of about one million kilometers.
The bright streaks run across some of Dione's many craters, indicating that the
process that created them occurred later than the
impacts that created those craters.
Dione
is made of mostly water ice but its relatively high density
indicates that it contains much rock inside.
Giovanni Cassini discovered Dione in 1684.
The Cassini spacecraft is scheduled to photograph Dione
at higher resolution in mid-December.
Currently, the
highest resolution images of
Dione remain those taken by the passing
Voyager spacecraft in 1980.
APOD: 2003 February 22 - Infrared Saturn
Explanation:
This delightfully detailed
false-color
image of Saturn was taken in January 1998 by the
orbiting Hubble Space Telescope.
The picture is a combination of three images from Hubble's
NICMOS instrument and shows the lovely ringed planet in reflected
infrared
sunlight.
Different colors indicated varying heights and compositions of cloud
layers generally thought to consist of ammonia ice crystals.
The eye-catching rings cast a shadow
on
Saturn's upper hemisphere.
The bright stripe seen within the left portion of the shadow
is infrared sunlight streaming through the large
gap
in the rings known
as the Cassini Division.
Two of
Saturn's many moons have also put in an appearance,
Tethys just
beyond the planet's disk at the upper right, and Dione at the lower left.
Presently, Saturn shines brightly in evening skies as a
pale yellow "star" near the constellation
Orion.
APOD: July 24, 1999 - Infrared Saturn
Explanation:
This delightfully detailed
false color image of Saturn
was earmarked to
celebrate the 8th anniversary of the orbiting Hubble Space Telescope.
The picture is a combination of three images taken in January 1998
and shows the lovely ringed planet in reflected
infrared light.
Different colors indicated varying heights and compositions of cloud
layers generally thought to consist of ammonia ice crystals.
The eye-catching rings cast a shadow
on Saturn's upper hemisphere,
while the bright stripe seen within the left portion of the shadow
is infrared
sunlight streaming through the large
gap in the rings known
as the Cassini Division.
Two of
Saturn's many moons have also put in an appearance,
Tethys just
beyond the planet's disk at the upper right, and Dione at the lower left.
APOD: April 24, 1998 - Infrared Saturn
Explanation:
This delightfully detailed
false color image of Saturn
has been earmarked to
celebrate the 8th anniversary of the orbiting Hubble Space Telescope.
The picture is a combination of three images taken in January of this year
with the Hubble's new NICMOS instrument and shows the lovely ringed planet in reflected
infrared light.
Different colors indicated varying heights and compositions of cloud
layers generally thought to consist of ammonia ice crystals.
The eye-catching rings cast a shadow
on Saturn's upper hemisphere,
while the bright stripe seen within the left portion of the shadow
is infrared
sunlight streaming through the large
gap in the rings known
as the
Cassini Division.
Two of
Saturn's many moons have also put in an appearance,
Tethys just
beyond the planet's disk at the upper right, and Dione at the lower left.
APOD: January 18, 1998 - Saturn, Rings, and Two Moons
Explanation:
NASA's robot spacecraft
Voyager 2 made this image of Saturn as it
began to explore the Saturn system in 1981.
Saturn's famous rings are visible along with two of
its moons,
Rhea and
Dione
which appear as faint dots on the right
and lower right part of the picture.
Astronomers believe that Saturn's moons play a
fundamental role in sculpting its elaborate ring system.
A robot spacecraft named
Cassini was
launched last October and is expected to
rendezvous with the giant gas planet in 2004.
APOD: May 31, 1997 - Saturn with Moons Tethys and Dione
Explanation:
Saturn and two of its larger moons -
Tethys and
Dione - were photographed by the
Voyager 1
spacecraft which flew by the planet in November of 1980.
This picture gives an indication of
Saturn's extensive ring system, which
can be seen casting a shadow on the planet, as does Tethys.
Saturn's rings are composed of many chunks of ice ranging in size
from a pebble to a car. The rings have several large gaps, the largest of
which is clearly visible in the picture and is named the
Cassini
Division, after its
discoverer.
Saturn
appears brighter than most stars in the sky,
and its rings can be discerned with a small telescope.
A new spacecraft -
Cassini - will visit
Saturn
and is currently scheduled for launch later in 1997.
APOD: May 12, 1996 - Tracking Saturn's Moons
Explanation:
These five pairs of
Hubble Space Telescope images track some of
Saturn's moons as they orbit the ringed planet.
A pair of images was taken every 97 minutes on November 21, 1995 with
the Wide Field Planetary Camera-2, the normally bright ring system
appearing nearly edge-on. In the top pair, the large
bright moon Dione hangs above center while the smaller moons
Pandora, Prometheus,
and Mimas (top right image)
appear near the planet's disk close to the outer ring. By the second and third
pair of images, moons Rhea
and Epimetheus have joined the dance.
During the Saturn ring plane crossings, the reduction in light from
the edge-on rings provided an opportunity for astronomer's to
explore Saturn's complex moon system and search for elusive
undiscovered satellites.
APOD: March 18, 1996 - Saturn with Moons Tethys and Dione
Explanation:
Saturn and two of its larger moons -
Tethys and
Dione - were photographed by the
Voyager 1
spacecraft which flew by the planet in November of 1980.
This picture gives an indication of
Saturn's extensive ring system, which
can be seen casting a shadow on the planet, as does Tethys.
Saturn's rings are composed of many chunks of ice ranging in size
from a pebble to a car. The rings have several large gaps, the largest of
which is clearly visible in the picture and is named the
Cassini
Division, after its
discoverer.
Saturn
appears brighter than most stars in the sky,
and its rings can be discerned with a small telescope.
A new spacecraft -
Cassini - will visit
Saturn
and is currently scheduled for launch in 1997.
APOD: October 10, 1995 - Dione's Lagrange Moon Helene
Explanation:
Saturn's moon
Helene
is very unusual in that it circles
Saturn near the
orbit of a bigger moon:
Dione.
Helene is situated in what is called a
"Lagrange point" of Dione - a place of stability created by Dione's
gravity. Were
Helene to stray slightly from its orbit 1/6 ahead of Dione,
the larger moon's gravity would cause Helene to move back toward the
Lagrange point. Many massive orbital bodies have stable Lagrange points,
including the Earth and Moon. Helene was discovered from the ground by P.
Laques & J. Lecacheux in 1980. The photograph above was taken by Voyager 2
as it passed Saturn in 1981. NASA's
Cassini
mission to Saturn is currently
scheduled for launch in October 1997.
APOD: October 9, 1995 - Saturn's Moon Dione
Explanation:
Dione, one of
Saturn's larger moons, is remarkable for its
bright surface streaks. These streaks run across some of Dione's many
craters, which indicate that the process which created the streaks occurred
later than the process which created the craters.
Dione
is made of mostly water ice but its relatively high density indicates that
it contains much rock inside. Dione was discovered by Giovanni Cassini in
1684. NASA's
Cassini
mission to Saturn is currently scheduled for launch in
October 1997. Dione's orbit is remarkable it that it also houses the much
smaller moon
Helene.
This moon, once designated "Dione B", precedes Dione by about 1/6th of an
orbit.
APOD: July 6, 1995 - Saturn, Rings, and Two Moons
Explanation:
This image of Saturn was made by NASA's robot spacecraft
Voyager
2 as it began to explore the Saturn system in 1981.
Saturn's famous rings are visible along with two of its moons, Rhea and
Dione which appear as faint dots in the right and lower right
part of the picture.
Astronomers believe that Saturn's moons play a fundamental
role in sculpting its elaborate ring system.