The Equinox Isn't What You Think It Is

[MUSIC] It was easy for our ancestors to figure out that every year, one day had the fewest hours of daylight, and one day had the most, and these made an easy way to divide the year th ings, inwe h dalivf.id ed it again, marking days halfway between the Th e equitwnoo.xe s: the day when theres equal day and night.

Except day and night on the equinoxes isn't equal.

And theyre not halfway between the shortest and longest days of the year.

The equinox probably isnt what you think it is.

[MUSIC] Instead of being a whole day, the equinox is one very specific moment, when Earths axis isn't pointing toward or away from the sun at all, which is also when the center of the sun crosses the equator.

But if exactly half of Earth is bathed in darkness and the equator is perpendicular to the sun, then why doesnt the equinox have equal day and night?

Because we mark “sunrise ” when the top of the sun rises above the horizon, and “sunset ” doesnt happen until the last sliver disappears, “day ” is several minutes longer than “night ” e of the eIfqu tinheox s.un were a point, instead of a disk, this wouldnt be a problem, but even then, the sun would appear to be up in the sky for longer, because near the horizon, Earths atmosphere acts like a lens, bending the suns rays to make them visible even when its As aal rreesaduly t,dr tophepe dd atbee lowhw.en night and day are exactly equal, the equilux, happens a few days earlier than the equinox in March, and a few days later in September, although precisely when depends on your latitude.

And because Earths orbit is elliptical, the solstices and equinoxes dont divide the year into even halves or quarters.

Because of gravity, as Earth gets closer to the sun, it travels slightly faster in its solar orbit, which means theres more days on the June side of the equinoxes than on the December side.

and so on.

For the same reason, in the northern hemisphere we get a few more days between the summer solstice and the winter solstice than vice versa.

So while the name might mean “equal night ”, each equinox has a bit more day, as sure as the sun rises in the east and sets in the west Stay curious.