Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

2014 September 22

Earth at Equinox
Video Credit: Roscosmos / NTSOMZ /
Courtesy: Igor Tirsky, Vitaliy Egorov

Explanation: Earth is at equinox. Over the next 24 hours, day and night have nearly equal duration all over planet Earth. Technically, equinox transpires at 2:29 am Universal Time tomorrow, but this occurs today in North and South America. This September equinox signal that winter is approaching in the northern hemisphere, and summer is approaching in the south. At equinox, the dividing line between the sunlit half of Earth and the nighttime half of Earth temporarily passes through Earth's north and south spin poles. This dividing line is shown in clear detail in the featured video, taken by the Russian meteorological satellite Elektro-L during last year's September equinox. The Elektro-L satellite is in geostationary orbit over one spot on Earth's equator and always points directly toward the Earth. The featured video shows a time lapse for an entire day surrounding the equinox, with a new image taken every 30 minutes. Cloud motions are visible as well as the reflection of the Sun are visible as the equinox day progressed. The next Earth equinox is scheduled for March.

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