The winter of our solsticular discontent

By Phil Plait | December 21, 2009 10:09 am

Happy winter solstice!


Today, at 17:47 GMT, the Sun reaches the southernmost point in its annual up-and-down journey in the sky. Because the Earth’s axis is tilted, the Sun gets higher in the sky in the summer, and lower in the winter. Today marks the moment when the center of the Sun just kisses that lowest point. From here on out, every day until the summer solstice next June, the Sun will get higher in the sky at local midday.

If you’re in the southern hemisphere, reverse that — replace higher with lower, winter with summer, color with colour, and peanut butter with Vegemite. I’d explain in detail, but that’s what you get for living standing on your heads all the time.

The winter solstice marks the longest night and shortest day of the year. However, it’s not when the Sun rises latest and sets earliest! The Earth has the unfortunate habit of orbiting the Sun in an ellipse, which screws things up a bit when it comes to timing. The actual rise and set times depend on your latitude, but for me, for example, in Boulder, the latest sunrise occurs in the first week of January, and the earliest sunset already happened in early December. Craziness! But the Earth is a crazy place.

If you want more information on this than you could possibly ever need, then try reading the Analemma website. Very cool stuff there. Or you could read what I wrote about this in 2005, 2006, 2007, and 2008.

Still and all, the good news here is that if you live above the equator, the days’re getting longer after today: the Sun will stay up a wee bit more every day. And that means soon it’ll be spring (when eggs will stand on end, just like they do EVERY FRAKKIN’ DAY), and then summer and then autumn and then we’ll be right back here again, as the Earth has done time and again, billions of times, and will continue to do so until the Sun swells into a red giant and consumes it in a fiery blaze of overwhelming solar red gigantism.

But until then, happy new year, too!

Image credit: NASA.

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