September equinox

The September equinox (or southward equinox) is the moment when the Sun appears to cross the celestial equator, heading southward. Due to differences between the calendar year and the tropical year, the September equinox can occur at any time between September 21 and 24.

UT date and time of
equinoxes and solstices on Earth[1][2]
event equinox solstice equinox solstice
month March June September December
yeardaytimedaytimedaytimedaytime
2016 2004:312022:352214:212110:45
2017 2010:292104:252220:022116:29
2018 2016:152110:072301:542122:22
2019 2021:582115:542307:502204:19
2020 2003:502021:432213:312110:03
2021 2009:372103:322219:212115:59
2022 2015:332109:142301:042121:48
2023 2021:252114:582306:502203:28
2024 2003:072020:512212:442109:20
2025 2009:022102:422218:202115:03
2026 2014:462108:252300:062120:50
Illumination of Earth by the Sun on the day of an equinox

At the equinox, the Sun as viewed from the equator rises due east and sets due west. Before the Southward equinox, the Sun rises and sets more northerly, and afterwards, it rises and sets more southerly.

The equinox may be taken to mark the end of astronomical summer and the beginning of astronomical autumn (autumnal equinox) in the Northern Hemisphere, while marking the end of astronomical winter and the start of astronomical spring (vernal equinox) in the Southern Hemisphere.[3]

The Autumnal and Spring equinoxes mark the point in the calendar at which the length of night and the length of day are almost exactly equal.