Spring is here
Monday, March 31st, 2008
The first day of spring is around March 20 or 21, depending on what day the vernal equinox occurs. This is when the sun sits directly above the equator on its apparent trip northward. Of course this sun isn’t moving; Earth is. As Earth revolves around the sun, the top half, called the Northern Hemisphere, becomes tilted more toward the sun as winter turns to spring. Meanwhile the bottom half, the Southern Hemisphere, becomes tilted more away from the sun. The beginning of spring for us is the beginning of autumn for people in Australia and the southern parts of Africa and South America.
Unequal equinox
The word “equinox” comes from Latin and means “equal nights.” Around March 20, sunrise and sunset are about twelve hours apart everywhere on Earth. Because of that, a lot of people think that day and night are of equal length on March 20. But actually the day is a little longer than the night on this date. There are a few reasons for that. Sunrise occurs when the top of the sun (not the center) is on the horizon. But the sun actually appears to be above the horizon when it is in fact still below it. That’s because Earth’s atmosphere refracts or “bends” light coming from the sun, so we see the sun a couple of minutes before it actually rises over the horizon. If you add the daylight that persists after sunset, you’ll find the day on the equinox is several minutes longer than the night.
