At around 6 am local time each day the Sun, Earth, and any geosynchronous satellite form a right angle giving a straight down view of the terminator, the edge between dusk and dawn.
The angle of the terminator varies with the seasons, causing the different day lengths and the amount of warmth we feel from the sunshine.
The Spinning Enhanced Visible and Infrared Imager (SEVIRI) on EUMETSAT’s Meteosat-9 captured these images of Earth from geosynchronous orbit. Although the Earth is fixed in the video it illustrates just how much it tilts throughout the year. The axis is tilted away from the Sun during winter solstice and toward it for summer solstice. At equinoxes the tilt is at a right angle to our star.
Autumn equinox occurred yesterday (23rd September 2011) at 09:04 UTC/GMT. Equinox means “equal night” in Latin, but while that is true of the Sun’s presence above the horizon it doesn’t account for twilight, when the Sun’s rays extend from beyond the horizon to illuminate the atmosphere.
I like this video a lot
NASA images and animation by Robert Simmon, using data from EUMETSAT. Caption by Mike Carlowicz.
YouTube video uploaded by: camillasdo