Friday, March 20, 2009
Happy First Day of Spring!
You don’t have to look far to see signs of spring. From the budding of the trees and the warming of the temperatures to the animals coming out of their winter hideouts, there seems to be a promise of new birth and color in the springtime air.
The first day of spring in the U.S. is considered to be 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. So it is autumn for people in Australia and the southern parts of Africa and South America.
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.
Variety in Spring Weather
In the United States, spring is a time of transition not only for plant and animal life, but for the weather too. It can mean weather extremes from very cold and snowy days to humid and stormy days. Some of the country's biggest snowfalls have occurred in March, and the period from March to May is the time of year when much of the south is most likely to get severe thunderstorms with hail and even tornadoes. This is why the beginning of spring is a good time to put together a plan for what you and your family would do in case of a severe thunderstorm or tornado.