Hello, Fall! (Tomorrow, That Is) So What is Autumn?

With Friday the last full day of summer 2012, fall is just hours away – and that means another autumnal equinox will be upon us on Saturday.

(If you really need to know, the exact moment of the autumnal equinox is at 10:49 a.m. on Sept. 22.)

But what is the autumnal equinox? Most people don't quite know, so let Belmont Patch serve as the great explainer for all things equinoctial.

Equinoxes fall on the halfway point between solstices and occur, according to the Washington Post, "when the sun crosses the equator and day and night are of roughly equal length, everywhere in the world."

The nearly equal 12 hours of light and darkness can be attributed to the Earth's lack of an axial tilt on the day of the equinox. In fact, the word equinox is derived from the Latin words aequus, meaning equal, and nox, meaning night.

In Belmont on the autumnal equinox, according to sunrisesunset.com, the sun will come up at 6:33 a.m. and set at 6:44 p.m. As you notice, that is not actually a perfect 12 hours of light and darkness. As timeanddate.com reports, this is because of issues such as light refraction and other reasons.

And for everyone who is inclined to celebrate the coming of fall, the Harvard Square Business Association and Revels is holding an Autumnal Equinox Celebration on Sunday (OK, they're a day late but who's counting?) Sept. 23. The festivities begin in historic Winthrop Park at 3 p.m. and culminate with the 9th Annual RiverSing communal singing concert on the Charles River at 6 p.m.

If you're interested in celebrating in a truly unique, and less hectic fashion, join the Sudbury Valley Trustees for a canoe trip down the nearby Concord River. You'll be on the river when the equinox takes place for this area. Check out additional information and register online at the link above.

So, so long shorts, whites and flip flops. Hello fall, and happy autumnal equinox!