But traditionally, fall begins promptly with the autumn equinox.
The equinox occurs twice a year. The vernal equinox happens around March 21, when the sun moves north across the celestial equator. The autumnal equinox occurs around September 22nd or 23rd, when the sun crosses the celestial equator going south.
The word equinox comes from Latin and means equality of night and day. Contrary to popular belief, the equinox doesn’t last for 24 hours. It occurs at two specific moments in time when the sun is exactly above the equator. In 2016, the Northern Hemisphere’s moment for the autumnal equinox is Thursday, September 22, at 14:21 UTC—that’s 10:21 a.m. in Boston, and 7:21 a.m. in San Francisco.
If you want to be truly egalitarian, opt for saying March equinox and September equinox. These terms avoid the Northern Hemisphere bias that March is in the spring and September is in the autumn.
The equinox is often confused with the solstice, which is either of the two times a year when the sun is at its greatest distance from the celestial equator. The solstice occurs around June 21 and December 22. Solstice derives from the Latin solstitium, which literally means “the standing still of the sun.”
The equinox has inspired a number of false beliefs, including that the event causes a massive disruption of communication satellites, or that on the equinox an egg can effortlessly be balanced on its end.
Are there natural phenomena you’d like us to examine? Events, physical occurrences, holidays you’d like us to define and unwind? Let us know, right below. And all of Dictionary.com wishes you a happy autumn!