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Spring starts Sunday, but what does that actually mean?

Vernal equinox delivers equal day and night, more or less
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Posted at 10:41 AM, Mar 16, 2022
and last updated 2022-03-16 13:41:10-04

LAS VEGAS (KTNV) — The spring equinox is Sunday, March 20, at 8:33 a.m. in Las Vegas. That means the sun will be directly over the equator at this time as the northern hemisphere tilts toward the sun.

In a few months, the sun will be directly over the Tropic of Cancer, 23.5° north latitude, on the summer solstice on June 21.

Both the spring and fall equinoxes are thought of as having equal day and night, although based on how we measure the start of sunrise and finish of sunset, that's not quite accurate.

March 16 is actually closest to equal day and night, with 11 hours, 59 minutes, and 16 seconds of daylight. To be fair, this is more of a bookkeeping note than anything: the start of sunrise is when the top of the sun rises in the east (when the sun is first visible on the flat horizon, removing the effect of any topography that may block the view), and the finish of sunset is when the top of the sun vanishes in the west (again, calculated assuming a flat, unimpeded view).

This means that on the equinox, there is actually a bit more daylight than darkness, to the tune of 12 hours, 8 minutes, and 29 seconds.

An interesting tidbit is that the sunrise happens directly in the east on the equinox, and the sunset is directly in the west.

Another fun fact: the sun is 90° over the equator at the start of spring, i.e. at its zenith, or, directly overhead.

Las Vegas is located at approximately 36° north latitude, and our sun angle on the equinox is 54°.

It's not a coincidence that the math works out!