There are copiousness of annual events that symbol a commencement of fall: a Labor Day holiday, a attainment of Pumpkin Spice Lattes during Starbucks, a changing colors of a leaves, a initial strenuous titillate to wear a sweater given a finish of spring. But there’s usually one central start of a season, and that’s a autumnal equinox, that arrives this Wednesday, Sept. 23., according to a U.S. Naval Observatory.
As TIME has explained before: “While that competence sound like a name of a place where hunks carve their biceps, a word comes from a Latin tenure aequinoctium, definition equivalence between day and night (aequi = equal and noct = night). That is what [the equinox] is after all: one of a dual durations of a year when a object crosses a equator and a days and nights are in equal length all over a earth.”
If we wish to get really technical, day and night aren’t indeed ideally equal on a tumble equinox. That’s since a equinox is strictly noted by a day a core of a object sets accurately 12 hours after it rises everywhere in a world—while a length of a day is totalled differently, formed on a time a really tip of a object rises and sets, according to a U.S. Naval Observatory. But a measurements are tighten adequate that day and night are approximately equal for several days around a equinox.
While it’s technically still summer until Sept. 23, that doesn’t meant it hasn’t already started feeling like fall—just demeanour during this TIME interactive graphic that marks a attainment of temperatures we many associate with autumn.