The equinox dates vary because of the difference between how the Gregorian calendar defines a year (365 days) and the time it actually takes for Earth to complete its orbit around the Sun (about 365 and 1/4 days). The last September 24 equinox occurred in 1931, the next one will take place in 2303. However, in the 21st century, it will happen twice-in 20. A September 21 equinox has not happened for several millennia. While the September equinox usually occurs on September 22 or 23, it can very rarely fall on September 21 or September 24. Statue of Pope Gregory XIII Bologna, Italy. The September equinox is also known as the vernal or spring equinox in the Southern Hemisphere and is considered by astronomers as the first day of spring there. In the Southern Hemisphere, the September equinox is the vernal (spring) equinox. The fall season ends on the December solstice, when astronomical winter begins.įor meteorologists, on the other hand, fall in the Northern Hemisphere begins about 3 weeks before the September equinox on September 1 and ends on November 30. Astronomically, the September equinox is the autumnal, or fall, equinox marking the end of summer and the beginning of fall (autumn). The September equinox is on or around September 22, while the first equinox of the year, the March Equinox, takes place on or around March 21 every year. Business Date to Date (exclude holidays).

2021 equinox fall