Sliver of Daylight
December 23, 2002
At first glance, there's not much to see on this visible satellite image, taken over the Indian Ocean. The image date is December 20 - just one day before the solstice. For the Northern Hemisphere, December 21 is the first day of winter, and it's the first day of summer in the Southern Hemisphere. The sliver of light at the lower left and bottom of the image confirms that indeed it's summer in the Southern Hemisphere. Note that the terminator, or edge of night, extends from over the Southern Atlantic Ocean to Antarctica, where the Sun is now up all day. At the South Pole, the Sun won't set again until March 21. The Earth's Southern Hemisphere is currently tilted (23 1/2 degrees) toward the Sun, thus the Sun's direct rays at noon fall over the Tropic of Capricorn (23 1/2 degrees south of the Equator) rather than over the Equator. On the above image, taken 22,000 miles (35,000 km) above the Equator, the Sun has just set over the southern tip of South Africa, while at all latitudes to the north, at the same longitude, it's already dark.