Watching solstices and equinoxes from space Jun 20, 2015 by EarthSky in Videos »

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Watching solstices and equinoxes from space
Jun 20, 2015
by EarthSky in Videos » Science Wire, Space

How sunlight falls on Earth’s surface during the solstices and equinoxes, as seen from geosynchronous orbit.

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EUMETSAT‘s Meteosat-9 (a weather satellite) captured the four views above of Earth from geosynchronous orbit a few years ago. A satellite in geosynchronous orbit stays over the same point on Earth all the time. The images above show how sunlight fell on the Earth on December 21, 2010 (upper left), March 20 (upper right), June 21 (lower left), and September 20, 2011 (lower right). Each image was taken at 6:12 a.m. local time.

Around 6 a.m. local time each day, the sun, Earth, and any geosynchronous satellite form a right angle, affording straight-down view of Earth’s terminator line, that is, the line between our world’s day and night sides. The shape of this line between night and day varies with the seasons, which means different lengths of days and differing amounts of warming sunshine.

The line is actually a curve because the Earth is round, but satellite images show it in two dimensions only.

On March 20 and September 20, the terminator is a straight north-south line, and the sun is said to sit directly above the equator. On December 21, the sun resides directly over the Tropic of Capricorn when viewed from the ground, and sunlight spreads over more of the Southern Hemisphere. On June 21, the sun sits above the Tropic of Cancer, spreading more sunlight in the north.

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