Equinox - March Equinox & September Equinox

Equinox means "equal night." Because the Sun is positioned above the equator, day and night are about equal in length all over the world during the equinoxes.
March Equinox: March equinox or Spring Equinox is the movement when the sun crosses the true celestial equator – or the line in the sky above the earth’s equator – from south to north, around March 20 (or March 21) of each year. At that time, day and night are balanced to nearly 12 hours each all over the world and the earth’s axis of rotation is perpendicular to the line connecting the centers of the earth and the sun. March 20, 2012, is a date that most of us recognize as symbolic of changing seasons. As we welcome spring, people south of the equator are actually gearing up for the cooler temperatures of autumn. 
September equinox: A second equinox occurs each year on Sept. 22 in 2012, it will be on Sept. 22 at 10:49 A.M. EDT. The September equinox occurs at 14:49 (or 2.49pm) Coordinated Universal Time (UTC) on September 22, 2012. It is also referred to as the autumnal or fall equinox in the northern hemisphere, as well as the spring or vernal equinox in the southern hemisphere (not to be confused with the March equinox). This is due to the seasonal contrasts between both hemispheres throughout the year.

Related Quiz: Question asked in RAS Pres Exam 2008 (Geography)
3. Spring equinox falls on (A) March 21
(B) June 21
(C) September 23
(D) December 22
ANSWER: March 21