If you live in the Northern Hemisphere of the Earth, then today is Autumnal Equinox. If you live in the Southern Hemisphere of the Earth, then today is Vernal Equinox. It is one of two days of the year, when there is a moment in time, where the Earth's axis is tilted neither towards nor away from the Sun. It is also the day when there is 12 hours of daylight and 12 hours of night. By the way, there is always 12 hours of daylight and night at the equator.
The Equinox will occur today at 21:18 UTC (roughly equivalent to GMT) or 16:18 EST.
One urban legends that is linked to Equinox is that you can balance an egg on its end during the equinox, but you can do that any day of the year(given enough patience).
Most American consider the Autumnal Equinox as the start of Autumn, but to most Asian cultures (including Chinese, Japanese, and Korean) it represents the middle of the autumn season and is celebrated with harvest festivals.
So whether you consider today the beginning or middle of Autumn in the Northern Hemisphere or the beginning or middle of Spring in the Southern, Happy Equinox!!