Spring is finally here with the arrival of the vernal equinox, as determined by people who base their seasons on the Earth’s position relative to the sun and stars. Here are five things to know:
1. What is it? During the vernal equinox, the sun shines directly on the equator, and the northern and southern hemispheres get exactly the same amount of rays. Night and day are almost equal length.
2. What does equinox mean? The Earth spins on a tilted axis, which means its northern and southern hemispheres trade places in receiving more light as it orbits the sun. The axis is not inclined toward or away from the sun at the equinox, which is derived from the Latin words for equal (aequus) and night (nox).
3. Why is it important? For ancient societies, the vernal and autumnal equinoxes marked when winter turned to spring and when summer turned to fall, respectively, and helped people track time-sensitive things, such as when to plant crops.
4. Didn’t spring start already? It might feel as if it has. Austin has had unseasonably warm temperatures for much of winter, even reaching 90 degrees March 10.
5. Forecasters’ spring started March 1: Meteorologists like to start the season March 1 because they prefer a calendar in which the seasons start on the same days every year. It helps with record keeping, among other reasons. But the Earth, sun and stars don’t quite conform to the Gregorian calendar — thus the vernal equinox doesn’t fall on the same day every year.