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.
Northward equinox solar year
|UT date and time of
equinoxes and solstices on Earth
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. 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.  provided the following examples of intervals between northward equinoxes:
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.
- 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.
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.
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 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.
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.
- Abrahamic tradition
- The Jewish Passover usually falls on the first full moon after the northern hemisphere vernal equinox, although occasionally (currently three times every 19 years) it will occur on the second full moon.
- The Christian Churches calculate Easter as the first Sunday after the first full moon on or after the March equinox. The official church definition for the equinox is March 21. The Eastern Orthodox Churches use the older Julian calendar, while the western churches use the Gregorian calendar, and the western full moons currently fall four, five or 34 days before the eastern ones. The result is that the two Easters generally fall on different days but they sometimes coincide. The earliest possible Easter date in any year is March 22 on each calendar. The latest possible Easter date in any year is April 25.
- West Asia
- The northward equinox marks the first day of various calendars including the Iranian calendar. The ancient Iranian new year's festival of Nowruz can be celebrated March 20 or March 21. According to the ancient Persian mythology Jamshid, the mythological king of Persia, ascended to the throne on this day and each year this is commemorated with festivities for two weeks. These festivities recall the story of creation and the ancient cosmology of Iranian and Persian people. It is also a holiday celebrated in Azerbaijan, Afghanistan, Pakistan, Turkey, Zanzibar, Albania, and various countries of Central Asia, as well as among the Kurds. As well as being a Zoroastrian holiday, it is also a holy day for adherents of the Bahá'í Faith and the Nizari Ismaili Muslims. The Bahá'í Naw-rúz is calculated using astronomical tables - the new year always starts at the sunset preceding the vernal equinox calculated for Tehran.
- In many Arab countries, Mother's Day is celebrated on the northward equinox.
- North Africa
- Sham el-Nessim was an ancient Egyptian holiday which can be traced back as far as 2700 BC. It is still one of the public holidays in Egypt. Sometime during Egypt's Christian period (c. 200–639) the date moved to Easter Monday, but before then it coincided with the vernal equinox.
- 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.
- In Manipur, this day marks the beginning of a new year of the Meetei lunar calendar and the day is celebrated as Cheiraoba by the Meeteis in Manipur. Since Meeteis use lunar calendar for its religious and social and religious festivals, the day varies from year to year and Cheiraoba is observed on the first day of Sajibu (the first month of Meetei lunar calendar).
- It marks the beginning of the new year of the Tamil calendar and is celebrated in the South Indian state of Tamil Nadu.
- This day is celebrated as the last day of the year according to the Bengali calendar and Assamese calendar in West Bengal, Assam, Tripura, Bangladesh and throughout Eastern and North Eastern India. The day is known as Chaitra Sankranti in Bengali. The following day is celebrated as the Bengali New Year's Day and Assamese Bihu.
- In Andhra Pradesh, Telangana, Karnataka and Maharashtra people celebrate new year ugadi set by Satavahana on the first morning after the first new moon from the sidereal vernal equinox. Also the calculations of the great Indian mathematician Bhaskaracharya proclaim the Ugadi day as the beginning of the New Year, New month and New day.
- In the Indian state of Odisha, this day is celebrated as the New Year around April 14. It is known as 'Vishuva Sankranti' (meaning "equal" in Sanskrit). In Kerala though the new year is on Chingam 1, the beginning of sidereal zodiac Leo, sidereal vernal equinox is celebrated much more than new year as 'Vishu'.
- The traditional New Year celebrations in Cambodia, Laos, Myanmar and Thailand take place on 13 to 15 (or 16) April.
- East Asia
- The traditional East Asian calendars divide a year into 24 solar terms (节气, literally "climatic segments"), and the vernal equinox (Chūnfēn, Chinese and Japanese: 春分; Korean: 춘분; Vietnamese: Xuân phân) marks the middle of the spring. In this context, the Chinese character 分 means "(equal) division" (within a season).
- In Japan, Vernal Equinox Day (春分の日 Shunbun no hi) is an official national holiday, and is spent visiting family graves and holding family reunions.
- The Americas
- Modern culture
- World Storytelling Day is a global celebration of the art of oral storytelling, celebrated every year on the day of the northward equinox
- World Citizen Day occurs on the northward equinox.
- In Annapolis, Maryland in the United States, boatyard employees and sailboat owners celebrate the spring equinox with the Burning Of The Socks festival. Traditionally, the boating community wears socks only during the winter. These are burned at the approach of warmer weather, which brings more customers and work to the area. Officially, nobody then wears socks until the next equinox.
- Neopagans observe the March equinox as a cardinal point on the Wheel of the Year. In the northern hemisphere some varieties of paganism adapt vernal equinox celebrations, while in the southern hemisphere pagans adapt autumnal traditions.
- International Astrology Day
- On March 20, 2014, the March equinox was commemorated by an animated Google Doodle.
- United States Naval Observatory (2015-09-21). "Earth's Seasons: Equinoxes, Solstices, Perihelion, and Aphelion, 2000-2025". Retrieved 2015-12-09.
- Meeus and Savoie (1992, p. 41)
- Dr. Irv Bromberg, University of Toronto, Canada. "The Lengths of the Seasons". Individual.utoronto.ca. Retrieved 2013-07-06.
- Ivan Smith (2002-05-10). "Vernal Equinox, 1452 - 1811". Ns1763.ca. Retrieved 2013-07-06.
- Ivan Smith (2002-05-10). "Vernal Equinox, 2188-2547". Ns1763.ca. Retrieved 2013-07-06.
- Cooley, Keith (2001). "Keith's Moon Facts". Hiwaay.net personal pages.
- "Navroz". The Ismaili. Islamic Publications Limited. Retrieved 2011-07-04.
- "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.
- "Disablót". Nationalencyklopedin (Swedish).
- "World Citizens Day - World Unity Day". Consultative Assembly of the Peoples Congress (2007).
- "Annapolis Welcomes Spring by Burning Socks". First Coast News.[not in citation given]
- Rey, Diane. "Hillsmere Joins in Sock Burning Tradition". The Capital. Annapolis, Maryland. Retrieved 25 April 2011.
- 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.