It's Autumn!

The Autumnal Equinox occurred at 5:04 US Eastern Time this morning. The Earth's axis stood straight up and down, relative to the sun, and autumn began. For our neighbors south of the equator, it's spring that's beginning. For them, this was the Equinoccio de Septiembre (Equinócio de Setembro in Brazil).

Contrary to popular belief, in most of the world today the hours of daylight and dark will not be equal in duration. Close but not quite. From TimeandDate.com:

During the equinox, the length of night and day across the world is nearly, but not entirely, equal. This is because the day is slightly longer in places that are further away from the equator, and because the sun takes longer to rise and set in these locations. Furthermore, the sun takes longer to rise and set farther from the equator because it does not set straight down - it moves in a horizontal direction.

Moreover, there is an atmospheric refraction that causes the sun's disk to appear higher in the sky than it would if earth had no atmosphere. timeanddate.com has a more detailed explanation on this topic. timeanddate.com has more information on why day and night are not exactly of equal length during the equinoxes.

I think that an Oktoberfest Lager will be called for tonight!

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• For many, Oktoberfest —the annual lager beer celebration held in Munich, Bavaria, Germany, and arguably the largest party in the world— is a sure sign of autumn's arrival. Oktoberfest actually begins in late summer and ends in early October. This year's festivities kicked off last Saturday, 17 September 2011, and will continue through Monday, 3 October. More than six million guests from around the world are expected to consume some 7.1 million Maßkrüge — one-liter mugs of beer, pronounced "MAHSS KREW-guh). That's 17 days of gemütlichkeit.
• The Washington Post has published a round-up of Oktoberfest celebrations in Washington, D.C., and its Maryland, and Virginia suburbs.