Autumnal Equinox 2014: Facts About the First Day of Fall
The sun's position in the sky dictates the equinoxes and solstices.
Say goodbye to summer: The Northern Hemisphere's autumnal equinox—the first day of fall—occurs Monday, September 22.
With its brilliant colors and crisper days, autumn is a favorite season for many. But what actually happens to make the seasons change? (See National Geographic's pictures of fall.)
The answer is the "clearly definable" position of the sun on the summer and winter solstices, the late Judith Young, a professor of astronomy at the University of Massachusetts in Amherst, told National Geographic News in 2011.
"The solstices are very accurately measured as the northernmost point that the sun rises along the horizon in June and the southernmost point along the horizon in December," she said. (See pictures of the sun's path across
