Today is the spring equinox, the first day of spring. But you may be surprised to learn some of the things that make this day so unusual. Earth rotates at an angle, but on the first day of spring and the first day of fall, that angle is such that the sun is directly over the equator. Thus, the entire planet experiences days and nights of the same length—12 hours of daylight and 12 hours of darkness. There is a slight variation from that time because of such things as mountains blocking the sun, curvature of the Earth, and even our definition of sunrise and sunset.
The exact dates of the spring and fall equinoxes vary slightly, but
they always fall near the 3rd week of the month. From now until the first day of
summer, in late June, days in the Northern Hemisphere will get longer and longer. After
that, they'll get shorter, and in late September, we will finally have another day
with 12 hours of light, worldwide.
Listen to the Audio (mp3 format) as recorded by KTEP, Public Radio for the Southwest.
Contributor: Robert Schmidt, Department of Geology, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.