Tonight's the equinox! Yay!
The timing of this is a bit funny. It's actually March 20 at 05:14 UTC, so it's 01:14 for eastern US folks, but actually on March 19 at 11:14 p.m. for us Mountain Timers. So I'm posting this now to make sure everyone gets a chance to see it.
Outside of astronomy, the equinox isn't that big of a deal. There are lots of ways of looking at it, but perhaps the easiest is to say that it's when the Sun rises due east and sets due west. It also means day and night are the same length, but that gets complicated: the Earth's air bends the light from the Sun so that we see it before it physically rises over the horizon and can still see it after it physically sets, adding a couple of minutes to the length of daylight. Another way to think of the equinox is that it's when the center of the Sun's disk is at the point on the sky where the Ecliptic (the path of the Sun on the sky over the year) intersects the Celestial Equator (the Earth's equator projected onto the sky).
I explain all this stuff in various earlier posts I've made on the equinoctes (which is the correct plural of equinox, it turns out). See Related Posts below.
One thing the equinox does not not NOT NOT mean is that you can balance ungainly objects on their ends on this day! This used to mean egg standing -- more on that in a sec -- but for reasons beyond my ability to parse the newest version of this involves standing brooms on their bristles. Don't believe me? Here's a gallery of people doing it. I've been hearing a lot about this, but it has nothing to do with the equinox (or the recent solar activity, another odd idea that's going around). It's actually a simply matter of center of mass and flat bristles. Honestly, it's not more mysterious than standing a brick up. Here's a good video explanation of it.
The picture above of the broom standing? That was taken on October 27, 2009. So there ya go. Also, you can try this: if you have a broom you can stand today, wait a week and try again. It'll stand then, too, if you try hard enough.
And finally, I'll leave you with this: how to stand an egg on end, equinox or equinot:
Image credit: Puuikibeach's Flickr photostream, used under Creative Commons license.