Happy equinox!

Happy equinox!

Happy equinox!

Bad Astronomy
The entire universe in blog form
Sept. 22 2007 5:42 PM

Happy equinox!

Sunday is the Autumnal Equinox, where day and night are the same length (except for a few minutes on either side caused by such trivialities as the ellipticity of the Earth's orbit and refraction due to the atmosphere, which makes daylight last longer).

On September 23 at 09:51 UT (5:51 a.m. Eastern US time) the Sun's position in the sky is exactly halfway between its farthest excursion north in the summer and the farthest south in winter (if you are in the southern hemisphere, swap the seasons). That's the actual definition of the equinox; it's an astronomical event that is only mildly connected to the seasons.

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You can also try standing an egg on end if you like... but make sure you try it again in a week.

Here in Boulder, you'd hardly notice. It was hot all week, and still pretty toasty as I write this. The mountains, kilometers away, are almost totally devoid of snow. I imagine in a month that scene will change, and in two months things will look a lot different. Snow again! Woohoo!

Of course, by December 22 -- the Winter Solstice -- we'll see how happy I am about cold weather.