No, not the Chevy!
Today, September 22nd, 2013 at precisely 4:44 p.m., the Earth passes a point in its orbit where the noonday Sun is exactly above the equator.
That instant marks the official transition from Summer to Autumn in the Northern Hemisphere. The name Equinox, derived from the Latin aequinoctium, means “equal day and night”.
On the the two days each year in September and in March when the Sun is exactly over the equator, the sunlight reaches all the way to the North Pole and the South Pole. On those two days, and those two days only, people on all parts of the Earth can observe the Sun rising exactly in the East and setting exactly in the West, and every spot on Earth measures exactly 12 hours of daylight and 12 hours of darkness. Equal day and night.
As the Earth continues hurtling around the Sun at 67,000 miles per hour, each night from now until December 21st will be just a bit longer than the previous night, and each day will be just a bit shorter than the day before.