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UT date and time of
equinoxes and solstices on Earth[1][2]
event equinox solstice equinox solstice
month March[3] June[4] September[5] December[6]
year day time day time day time day time
2017 20 10:29 21 04:25 22 20:02 21 16:29
2018 20 16:15 21 10:07 23 01:54 21 22:22
2019 20 21:58 21 15:54 23 07:50 22 04:19
2020 20 03:50 20 21:43 22 13:31 21 10:03
2021 20 09:37 21 03:32 22 19:21 21 15:59
2022 20 15:33 21 09:14 23 01:04 21 21:48
2023 20 21:25 21 14:58 23 06:50 22 03:28
2024 20 03:07 20 20:51 22 12:44 21 09:20
2025 20 09:02 21 02:42 22 18:20 21 15:03
2026 20 14:46 21 08:25 23 00:06 21 20:50
2027 20 20:25 21 14:11 23 06:02 22 02:43
Illumination of Earth by the Sun on the day of an equinox
Illumination of Earth by the Sun on the day of an equinox

The September equinox (or southward equinox) is the moment when the Sun appears to cross the celestial equator, heading southward. Because of differences between the calendar year and the tropical year, the September equinox may occur anytime from September 21 to 24.

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.[7]

Occurrences

Sunset at the equinox from the site of Pizzo Vento at Fondachelli Fantina, Sicily
Sunset at the equinox from the site of Pizzo Vento at Fondachelli Fantina, Sicily

See also: Tropical year

The September equinox is one point in time commonly used to determine the length of the tropical year.

The dates and times of the September equinoxes[8] that occur from the year 2017 to 2027 (UTC) are listed as follows:

Date time (UTC)
2017-09-22 20:01
2018-09-23 01:54
2019-09-23 07:50
2020-09-22 13:30
2021-09-22 19:21
2022-09-23 01:03
2023-09-23 06:50
2024-09-22 12:43
2025-09-22 18:19
2026-09-23 00:05
2027-09-23 06:01

Constellation

The point where the Sun crosses the celestial equator southwards is called the First Point of Libra. However, because of the precession of the equinoxes, this point is no longer in the constellation Libra, but rather in Virgo.

The solar point of the September equinox passed from Libra and into Virgo in −729 (730 BCE) and will enter Leo in 2439.

Apparent movement of the Sun in relation to the horizon

At the equinox, the Sun rises directly in the east and sets directly in the west. However, because of refraction it will usually appear slightly above the horizon at the moment when its "true" middle is rising or setting. For viewers at the north or south poles, it moves virtually horizontally on or above the horizon, not obviously rising or setting apart from the movement in "declination" (and hence altitude) of a little under a half (0.39) degree per day.

For observers in either hemisphere not at the poles, the Sun rises and sets more and more to the south during the 3 months following the September equinox. This period is the second half of a 6-month long southerly movement, beginning with the June solstice when the Sun rises and sets at its most northern point.

Culture

See also: March equinox § Culture

Calendars

The September equinox marked the first day of the French Republican Calendar.

Commemorations

West Asia

East Asia

Judaism

Europe

Neopaganism

Americas

See also

References

  1. ^ Astronomical Applications Department of USNO. "Earth's Seasons - Equinoxes, Solstices, Perihelion, and Aphelion". Retrieved August 1, 2022.
  2. ^ "Solstices and Equinoxes: 2001 to 2100". AstroPixels.com. February 20, 2018. Retrieved December 21, 2018.
  3. ^ Équinoxe de printemps entre 1583 et 2999
  4. ^ Solstice d’été de 1583 à 2999
  5. ^ Équinoxe d’automne de 1583 à 2999
  6. ^ Solstice d’hiver
  7. ^ "Defining Seasons". Time and Date AS. Retrieved May 31, 2019.
  8. ^ "Solstices & Equinoxes for UTC (Surrounding 10 Years)". www.timeanddate.com. Retrieved October 10, 2021.
  9. ^ "Autumnal Equinox Day (秋分の日): More Than Just a Change of Seasons". cotoacademy.com. September 23, 2017. Retrieved September 22, 2020.
  10. ^ "Visitors Guide to the Woodhenge". Retrieved December 19, 2017.
  11. ^ Iseminger, William. "Welcome the Fall Equinox at Cahokia Mounds". Illinois Department of Natural Resources. Retrieved December 20, 2017.
  12. ^ "Winter Solstice Sunrise Observance at Cahokia Mounds". Collinsville Chamber of Commerce. Retrieved December 20, 2017.
  13. ^ "Cahokia Mounds Mark Spring Equinox : The keepers of Cahokia Mounds will host a spring gathering to celebrate the vernal equinox". Indian Country Today. Indian Country Media Network. Retrieved December 20, 2017.