Fall is just around the corner for everyone in the Northern Hemisphere, while those in the Southern Hemisphere are bracing for warmer spring weather.
Depending on where you live in the world, the season will change on September 22 or 23. This is because the equinox is not a one-day event. Rather, the equinox is defined by the position of the earth and the sun at a particular moment in time.
Time zones are not the only source of confusion regarding the date of the equinox. To further complicate our calendars, the fall equinox can occur anytime between September 21 and 24. [Autumn Equinox: 5 Odd Facts About Fall]
On September 22 at 9:04 pm EDT (01:04 GMT on September 23), the sun will cross the celestial equator, or an imaginary line that projects Earth’s equator back into space. At this exact moment, the northern and southern hemispheres will receive the same amount of sunlight, and the length of day and night will be roughly the same around the world, hence the term “equinox,” which is derived from the Latin phrase meaning means “same”. night.”
Most years, this happens on September 22 or 23. However, from time to time, the autumnal equinox may occur on September 21 or 24. This happens because the duration of a calendar year (365 days) is not equal to the time it takes for the Earth to go around the sun (365.25 days). To compensate for this inconsistency, people have observed “leap years” for the past two millennia. By adding a “leap day” (February 29) to the calendar every four years, we have managed to keep our seasons more or less consistent year after year.
However, leap years do not ensure that the equinoxes always fall on the same date. “Because of leap years, the dates of the equinoxes and solstices can change by a day or two over time, causing the start dates of the seasons to change as well,” according to The Old Farmer’s Almanac.
The last time the fall equinox fell on September 21 was over a thousand years ago, and the last equinox on September 24 was in 1931. according to timeanddate.com. While it has been a long time since the September 21st equinox occurred, we can expect it to occur twice in the next century, first in 2092 and then in 2096. The next September 24th equinox will be in the year 2303. (Please note Note that these dates are based on universal time, so some time zones may not experience these equinoxes on the dates listed here).
EDITOR’S NOTE: This article was updated on September 19, 2022 to reflect the date and time of the 2022 autumnal equinox.
Originally published on Space.com.