Autumnal Equinox 2010

New York (GaeaTimes.com) - The date of the Autumn Equinox is referred to that day when the Sun crosses the celestial equator which is moving in southward direction. It is also based on that day when night and day are nearly of the same duration. It is referred as the first day of autumn. This day is very close to the date 21st September.

In the northern hemisphere, the September equinox is also referred to as the autumnal or fall equinox. The spring equinox is also known as vernal equinox in the southern hemisphere. This happens due to the difference in season between both hemispheres all through the year. The equinox occurs on September 22, 2010 in the evening. This happens for locations on US Eastern Daylight Time or further west.

During the Autumn Equinox, the sun crosses the equator. It moves southward in the northern hemisphere. The subsolar point is that point on the earth where the sun is directly overhead at solar noon. In the September equinox, the subsolar point occurs on top of the equator. Then the axis with which the Earth rotates is 90 degree to the line which connects the centers of the earth and the sun.

The duration of night and day across the world during the equinox is not exactly equal. The reason behind it is that those places which are slightly further away from the equator experiences a longer sunrise. There is also an atmospheric refraction. It causes the sun to appear higher in the sky as if there is no atmosphere. The equinox dates are not the same each year. The September equinox occurred on September 22nd in the year 2008 and 2009. It will occur on September 23rd in the year 2010 and 2011.The Autumn Equinox has also occurred previously on September 24. This happened last in the year 1931.