Astronomy Picture of the Day

Explanation: Today the Sun crosses the celestial equator heading south -- marking the Autumnal Equinox, the first day of Autumn. Equinox means equal night and with the Sun on the celestial equator, Earthlings will experience 12 hours of daylight and 12 hours of darkness regardless of their location. Then, for those in the northern hemisphere, the days will begin to grow shorter with the Sun marching lower in the sky as winter approaches. A few weeks after the Autumnal Equinox of 1994, the Crew of the Shuttle Endeavor recorded this image of the Sun poised above the Earth's limb. The glare illuminates Endeavor's vertical tail (pointing toward the Earth) along with radar equipment in the payload bay.