March equinox

Illumination of Earth by the Sun on the day of an equinox

The March equinox or Northward equinox is the equinox on the Earth when the Sun appears to leave the southern hemisphere and cross the celestial equator, heading northward as seen from earth. In the Northern Hemisphere the March equinox is known as the vernal equinox, and in the Southern Hemisphere as the autumnal equinox.

On the Gregorian calendar the Northward equinox can occur as early as March 19 or as late as March 21. For a common year the computed time slippage is about 5 hours 49 minutes later than the previous year, and for a leap year about 18 hours 11 minutes earlier than the previous year. Balancing the increases of the common years against the losses of the leap years keeps the calendar date of the March equinox from drifting more than one day from March 20 each year.

The March equinox may be taken to mark the beginning of spring and the end of winter in the Northern Hemisphere but marks the beginning of autumn and the end of summer in the Southern Hemisphere.[1]

Northward equinox solar year

Main article: tropical year
UT date and time of
equinoxes and solstices on Earth[2]
event equinox solstice equinox solstice
month March June September December
year
day timeday timeday timeday time
2010 2017:322111:282303:092123:38
2011 2023:212117:162309:042205:30
2012 2005:142023:092214:492111:12
2013 2011:022105:042220:442117:11
2014 2016:572110:512302:292123:03
2015 2022:452116:382308:212204:48
2016 2004:302022:342214:212110:44
2017 2010:282104:242220:022116:28
2018 2016:152110:072301:542122:23
2019 2021:582115:542307:502204:19
2020 2003:502021:442213:312110:02

The March equinox is one point in time commonly used to determine the length of the tropical year. The mean tropical year is the average of all the tropical years measured from every point along the earth's orbit.[3] When tropical year measurements from several successive years are compared, variations are found which are due to nutation, and to the planetary perturbations acting on the Sun. Meeus and Savoie (1992, p. 41) provided the following examples of intervals between northward equinoxes:

time in excess of 365 days and 5 hours
mins
1985–1986 48 59
1986–1987 49 15
1987–1988 46 38
1988–1989 49 42
1989–1990 51 06

Constellation

The point where the sun crosses the celestial equator northwards is called the First Point of Aries. However, due to the precession of the equinoxes, this point is no longer in the constellation Aries, but rather in Pisces. By the year 2600 it will be in Aquarius.

Conditions at the Earth's horizon in relation to the Sun

In its apparent motion on the day of an equinox, the Sun's disk crosses the Earth's horizon directly to the east at dawn—rising; and again, some 12 hours later, directly to the west at dusk—setting. But an equinoctial day produces several minutes more daylight time than nighttime, for reasons that follow.

Due to refraction of light rays in the Earth's atmosphere the Sun, whether rising or setting, will, in part, show above the horizon even when its disc is completely below the limb of Earth's horizon. Also, viewed from the Earth, the Sun presents as an extended object (a disc) source of light rather than a point source of light, and its upper disk is visible even when the center of the Sun is below Earth's horizon. Thus, sunrise produces daylight several minutes before the Sun's geometric center crosses from below the horizon; a converse sequence occurs at dusk, and sunset produces daylight several minutes after the setting of the center of the Sun to below Earth's horizon. These conditions produce differentials of actual durations of light and darkness at various locations on Earth during an equinox; see lengths of equinoctial day and night.

To viewers at the north or south poles, the sun appears to move steadily around the horizon, and just above the horizon, neither rising nor setting apart from "movement in declination", i.e., elevation, which is about (0.39) degree per day.

Human culture

Calendars

The Babylonian calendar began with the first full moon after the vernal equinox, the day after the Sumerian goddess Inanna's return from the underworld (later known as Ishtar), in the Akitu ceremony, with parades through the Ishtar Gate to the Eanna temple, and the ritual re-enactment of the marriage to Tammuz, or Sumerian Dummuzi.

The Persian calendar begins each year at the northward equinox, observationally determined at Tehran.[4]

The Indian national calendar starts the year on the day next to the vernal equinox on March 22 (March 21 in leap years) with a 30-day month (31 days in leap years), then has 5 months of 31 days followed by 6 months of 30 days.[4]

Julian calendar

The Julian calendar reform lengthened seven months and replaced the intercalary month with an intercalary day to be added every four years to February. It was based on a length for the year of 365 days and 6 hours (365.25 d), while the mean tropical year is about 11 minutes and 15 seconds less than that. This had the effect of adding about three quarters of an hour every four years. The effect accumulated from inception in 45 BC until the 16th century, when the northern vernal equinox fell on March 10 or 11.

The date in 1452 was March 11 11:52 (Julian) [5] In 2547 it will be March 20 21:18 (Gregorian) and March 3 21:18 (Julian).[6]

Commemorations

Bas-relief in Persepolis – a symbol Iranian/Persian Nowruz – on the day of an equinox, the power of an eternally fighting bull (personifying the Earth) and that of a lion (personifying the Sun) are equal.
Chichen Itza pyramid during the spring equinox – Kukulkan, the famous descent of the snake
Abrahamic tradition
West Asia
North Africa
South and Southeast Asia

According to the sidereal solar calendar, celebrations which originally coincided with the vernal equinox now take place throughout South Asia and parts of Southeast Asia on the day when the sun enters the sidereal Aries, generally around 14 April.

East Asia
Europe
The Americas
Modern culture

See also

References

  1. ↑ https://www.timeanddate.com/calendar/aboutseasons.html
  2. ↑ United States Naval Observatory (2015-09-21). "Earth's Seasons: Equinoxes, Solstices, Perihelion, and Aphelion, 2000-2025". Retrieved 2015-12-09.
  3. ↑ http://individual.utoronto.ca/kalendis/leap/Solar-Year-Length-Variations.pdf
  4. 1 2 Dr. Irv Bromberg, University of Toronto, Canada. "The Lengths of the Seasons". Individual.utoronto.ca. Retrieved 2013-07-06.
  5. ↑ Ivan Smith (2002-05-10). "Vernal Equinox, 1452 - 1811". Ns1763.ca. Retrieved 2013-07-06.
  6. ↑ Ivan Smith (2002-05-10). "Vernal Equinox, 2188-2547". Ns1763.ca. Retrieved 2013-07-06.
  7. ↑ Cooley, Keith (2001). "Keith's Moon Facts". Hiwaay.net personal pages.
  8. ↑ "Navroz". The Ismaili. Islamic Publications Limited. Retrieved 2011-07-04.
  9. ↑ "With Spring comes the Baha'i New Year". Bahai.us. National Spiritual Assembly of the Baha'is of the United States. Retrieved 2011-07-04.
  10. ↑ "Disablót". Nationalencyklopedin (Swedish).
  11. ↑ "World Citizens Day - World Unity Day". Consultative Assembly of the Peoples Congress (2007).
  12. ↑ "Annapolis Welcomes Spring by Burning Socks". First Coast News.
  13. ↑ Rey, Diane. "Hillsmere Joins in Sock Burning Tradition". The Capital. Annapolis, Maryland. Retrieved 25 April 2011.
  14. ↑ Gander, Kashmira (2014-03-20). "Spring equinox 2014: First day of spring marked by Google Doodle". The Independent. independent.co.uk. Retrieved 2014-03-20.

External links

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