This page uses content from Wikipedia and is licensed under CC BY-SA.

March equinox

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

The March equinox[citation needed] or Northward equinox[citation needed] is the equinox on the Earth when the subsolar point 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.[citation needed]

On the Gregorian calendar the Northward equinox can occur as early as 19 March or as late as 21 March. 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 20 March 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 time day time day time day time
2010 20 17:32 21 11:28 23 03:09 21 23:38
2011 20 23:21 21 17:16 23 09:04 22 05:30
2012 20 05:14 20 23:09 22 14:49 21 11:12
2013 20 11:02 21 05:04 22 20:44 21 17:11
2014 20 16:57 21 10:51 23 02:29 21 23:03
2015 20 22:45 21 16:38 23 08:21 22 04:48
2016 20 04:30 20 22:34 22 14:21 21 10:44
2017 20 10:28 21 04:24 22 20:02 21 16:28
2018 20 16:15 21 10:07 23 01:54 21 22:23
2019 20 21:58 21 15:54 23 07:50 22 04:19
2020 20 03:50 20 21:44 22 13:31 21 10:02

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, many slight variations are found which are due to a variety of phenomena, including nutation and the planetary perturbations from the Sun.[4] The following table shows the small variations in timing over a long period of time; the mean Tropical year lasts 365 days, 5 hours, 48 minutes, 45 seconds.

Variation from average tropical year length
Year Variation
1985–1986 - 14s
1986–1987 - 30s
1987–1988 + 2m 7s
1988–1989 - 57s
1989–1990 - 2m 21s

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. The Earth's axis causes the First Point of Aries to travel westwards across the sky at a rate of roughly one degree every 72 years. Based on the modern constellation boundaries, the northward equinox passed from Taurus into Aries in the year −1865 (1866 BC), passed into Pisces in the year −67 (68 BC), will pass into Aquarius in the year 2597, and will pass into Capricornus in the year 4312. It passed by (but not into) a 'corner' of Cetus at 0°10′ distance in the year 1489.

Apparent movement of 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. The March equinox, like all equinoxes, is characterized by having an almost exactly equal amount of daylight and night across most latitudes on Earth.

Due to refraction of light rays in the Earth's atmosphere the Sun will be visible above the horizon even when its disc is completely below the limb of the Earth. Additionally, when seen from the Earth, the Sun is a bright disc in the sky and not just a point of light, thus sunrise and sunset can be said to start several minutes before the sun's geometric center even crosses the horizon, and extends equally long after. These conditions produce differentials of actual durations of light and darkness at various locations on Earth during an equinox. This is most notable at the more extreme latitudes, where the Sun may be seen to travel sideways considerably during the dawn and evening, drawing out the transition from day to night. 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 a slight change in declination of about 0.39° per day as the equinox passes.[3]

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.[5]

The Indian national calendar starts the year on the day next to the vernal equinox on 22 March (21 March 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.[5]

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 10 or 11 March.

The date in 1452 was 11 March, 11:52 (Julian) [6] In 2547 it will be 20 March, 21:18 (Gregorian) and 3 March, 21:18 (Julian).[7]

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. ^ [www.timeanddate.com]
  2. ^ United States Naval Observatory (21 September 2015). "Earth's Seasons: Equinoxes, Solstices, Perihelion, and Aphelion, 2000-2025". Retrieved 9 December 2015. 
  3. ^ a b Bromberg, Irv. "Solar Year Length Variations" (PDF). University of Toronto, Canada. 
  4. ^ Meeus and Savoie (1992, p. 41)[full citation needed]
  5. ^ a b Bromberg, Irv. "The Lengths of the Seasons". University of Toronto, Canada. Retrieved 6 July 2013. 
  6. ^ Smith, Ivan (10 May 2002). "Vernal Equinox, 1452–1811". Ns1763.ca. Retrieved 6 July 2013. 
  7. ^ Smith, Ivan (10 May 2002). "Vernal Equinox, 2188–2547". Ns1763.ca. Retrieved 6 July 2013. 
  8. ^ Cooley, Keith (2001). "Keith's Moon Facts". Hiwaay.net personal pages. [self-published source]
  9. ^ "Navroz". The Ismaili. Islamic Publications Limited. Retrieved 4 July 2011. 
  10. ^ "With Spring comes the Baha'i New Year". National Spiritual Assembly of the Baha'is of the United States. Retrieved 4 July 2011. 
  11. ^ "Disablót". Nationalencyklopedin (in Swedish). 
  12. ^ "World Citizens Day—World Unity Day". Consultative Assembly of the Peoples Congress. 2007. 
  13. ^ "Annapolis Welcomes Spring by Burning Socks". First Coast News. [not in citation given]
  14. ^ Rey, Diane. "Hillsmere Joins in Sock Burning Tradition". The Capital. Annapolis, Maryland. Retrieved 25 April 2011. 
  15. ^ Gander, Kashmira (20 March 2014). "Spring equinox 2014: First day of spring marked by Google Doodle". The Independent. London. Retrieved 20 March 2014. 

External links