What Is Vernal Equinox?

In astronomy, the vernal equinox (spring
equinox, March equinox, or northward equinox) is the equinox at the
beginning of spring in the northern hemisphere: the moment when the sun
appears to cross the celestial equator, heading northward.



The term can also be used to refer to the point on the sky defined as the
first point of Aries.



Considered as a time, rather than a point on the sky, the equinox occurs
from March 19 to March 21, the precise time being about 5 hours 49 minutes
later in a common year, and about 17 hours 26 minutes earlier in a leap
year, than in the previous year. (Refer to the 400-year cycle of leap
years at calendar
seasonal error).

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Nomenclature

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
(hence the term "the dawning of the Age of Aquarius").



In the Southern Hemisphere, the equinox occurs at the same moment, but at
the beginning of autumn. There are two conventions for dealing with this:
either the name of the equinox can be changed to the autumnal equinox, or
(apparently more commonly) the name is unchanged and it is accepted that
it is out of sync with the season. The alternative terms "March
equinox" or "northward equinox" (or even "vernal
equinox" for people prepared to ignore the etymology) avoid any such
ambiguity.

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Apparent Movement of Sun in Relation to 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 all slightly above the horizon at the moment when its
"true" middle is rising or setting. And for viewers at the north
or south poles it is moving 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 half a
degree per day - about 365.2/360 times the sine of 23.5 degrees.



For observers in either hemisphere not at the poles, the further one goes
in time away from the vernal equinox in the 3 months before that equinox,
the more to the south the sun has been rising and setting, and for the
three months afterwards it rises and sets more and more to the north.

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Holidays

The Iranian festival of Norouz is celebrated on the
vernal equinox, as is the Neopagan Sabbat of Ostara (or Eostar).
 



Also, in

Japan

Vernal Equinox Day (春分の日) is an
official national holiday and is spent visiting family graves and holding
family reunions.
 



Easter is celebrated on the Sunday after the first
ecclesiastical full moon day on or after the ecclesiastical vernal equinox
day 21 March (see computus).
 



Earth Day has been celebrated on the vernal equinox
each year since the first Earth Day on 21 March 1970.
 



Tamil New Year is celebrated after the vernal
equinox. This is celebrated in the South-Indian state of Tamil Nadu.

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Egg Balancing Myth

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