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? Meteorological spring started March 1. Forecasters like to start the season on the first day of March because they prefer a calendar in which each season starts on the same day 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.
5. What's next? The summer solstice is June 21, but meteorological summer begins a few weeks earlier on June 1.
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