In the wake of last week's equinox, the days are shorter than the nights in the Northern Hemisphere, and longer in the south. Every day from now until December will increase the imbalance. How does that happen? It has to do with Earth's changing tilt with respect to the sun, as explained in this tutorial. But sometimes a moving picture can be worth a thousand words.
This 12-second video clip has been assembled from a year's worth of imagery captured by a visible-light and infrared camera on EUMETSAT's Meteosat-9 satellite. Meteosat-9, like other satellites in geosynchronous orbit, has an unchanging view of Earth from a height of about 22,000 miles. Every day, around 6 a.m. local time, the satellite watches the terminator line between night and day move across Africa.
As it spins, Earth is tipped 23.5 degrees on its axis relative to the sun, with the northern point of the axis pointing away from the sun in December and pointing toward the sun in June. That means the Northern Hemisphere is more shadowed in winter and more sunlit in summer. That back-and-forth shift is exactly what you're seeing in the video. At the midpoints between those extremes — for instance, last week's equinox — the terminator line goes straight down the middle of Earth's disk, as seen by Meteosat-9.
Click on over to our tutorial or NASA's Earth Observatory posting to learn more about the changing seasons, as seen from space. And if you're still scratching your head over Earth's tilt, check out this video:
More views of Earth from space:
- Jupiter probe looks back at Earth and moon
- Deep Impact probe sends alien's-eye view of Earth
- Japan's moon probe updates Earthrise picture
- Rosetta comet probe takes Earth snapshot
- Rover spots Earth amid Martian sunrise
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