An equinox is one of the two days a year, in March and September, when the sun crosses the equator and day and night are nearly equal everywhere.

In 2026 they fall on March 20 and, by most clocks, September 23 — the instant is 00:05 UTC, so the Americas keep the 22nd. The sun's noon altitude that day equals 90° minus your latitude, and day length is changing by its most — about three minutes a day at 45°, and not at all at the equator. Day is a little longer than night even then, because refraction and the sun's width both count toward the day.

The sun rises due east and sets due west that day, at every latitude; the light changes fastest around it.