On 20 March, at 00:13 CDT, the sun will reach a point on its apparent path along the ecliptic where it
crosses the ‘celestial equator' moving northward from its December solstice position. The day of this occurrence, of which there are two,
is known as an equinox. The March Equinox marks the end of winter and the beginning of spring in the northern hemisphere.
Astronomically the sun has reached the celestial coordinates of 0 hours (right ascension), and 0 degrees (declination).
These are like the Earth surface-based grid system of latitude and longitude.
Click here to watch an animated graphic showing the Sun's apparent motion along the ecliptic during March. Geographically the sun is over the Earth's equator on this day and will rise approximately due east and set approximately
due west everywhere except at the poles. Historically the sun is located at the coordinates (not the constellation) that marked the beginning of
the year many thousands of years ago when the sun was ‘in' Aries.
Click here to watch a short video (flv format) about seasons on Earth. The ecliptic is the apparent path the sun follows throughout the year. This apparent motion of the sun is due to the Earth's
orbital motion around the sun. Since the Earth takes 365.25 days to complete the 360o revolution around the sun, the sun appears to move nearly 1o
eastward every day. From the day of the March Equinox the sun will continue to move northward until it reaches its maximum distance north (23.5o)
of the equator on the day of the June Solstice. This position on the Earth's surface is marked by the parallel of latitude known as the Tropic of Cancer .
Click here to read my Scope on the Skies column from March 2010 about measuring the rotational speed of the Earth. Click here to visit my Sun shadow project web site for some activities and other information about the equinox.
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