Vernal Equinox Ushers in Spring Monday

There's no "official" start of spring, but for most the vernal equinox, or spring equinox, marks the start of the season.

And it's starting soon. The vernal equinox will happen at 5:28 a.m. CDT on Monday, March 20, 2017.

That marks the time when the sun crosses over the equator and the length of days and nights will be almost equal.

Almost equal.

The day that comes the closest to having 12 hours of equal day and night was March 16.

For example, in Alabama on March 16 the day length is 12 hours and 6 seconds in Birmingham, 11:59:51 in Huntsville and 12:00:40 in Mobile.

Day length has been growing since the winter solstice last Dec. 21. It will continue to increase until the summer solstice.

The equinoxes also mark the two times each year when the Earth is not tilted either forward or away from the sun, according to EarthSky.org.

Our planet is tilted on its axis at about 23.4 degrees, and as it makes its yearly trip around the sun one hemisphere faces the sun more than the other, hence we have the seasons.

So while the vernal equinox marks the start of astronomical spring in the northern Hemisphere, it is also the onset of fall in the southern Hemisphere.

The summer solstice will be June 20, 2017, at 11:24 p.m.