Even though it happens year after year, the arrival of autumn is always a little surprising. Almost as if on a switch, one day late in the summer you feel it – a subtle crispness in the air. And before you know it, it’s pumpkin-spice-everything everywhere. We are suddenly swathed in sweaters and wearing boots and bombarded by shades of orange, often even before the thermometer warrants it. After slogging through a long hot August, it’s exciting.
We can thank the autumnal equinox for this shift from sultry summer to cozy fall. And while most of us are aware of when the first day of autumn lands on the calendar, there’s more to the equinox than meets the eye. Consider the following.
1. This year, the autumnal equinox arrives precisely at 10:21 a.m. (EDT) on Thursday, September 22. Unlike an event like New Year’s midnight that follows the clock around the time zones, equinoxes happen at the same moment everywhere.
2. There are two equinoxes annually, vernal and autumnal, marking the beginning of spring and fall. They are opposite for the northern and southern hemispheres.
3. The autumnal equinox happens the moment the sun crosses the celestial equator, which is an imaginary line in the sky that corresponds to Earth’s equator. (Old Farmer’s Almanac describes it as a plane of Earth’s equator projected out onto the sphere.) Every year this occurs on September 22, 23, or 24 in the northern hemisphere.
Some Additional Facts you might need to know to win those bets today: