A Long, Drawn-Out Solstice

 The winter solstice this year came on about December 22. It was the shortest day of the year, but not by much. There’s a ten-day stretch in which the earliest sunsets and latest sunrises of the year are within a minute of each other.

What I find interesting is that, while these time markers are nearly stationary at the solstice, one is actually going in one direction and the other in the other. In Southeast Michigan we had our earliest sunset around December 10, at 5:02 PM. At the solstice, the sun has begun its upward journey, and sets at 5:05 PM. Our latest sunrise will be at 8:04 AM, on about January 4. At the solstice, it is still getting later, at 8:01 AM.

At the other solstice in June, the same phenomenon occurs: earliest sunrise and latest sunset are moving in opposite directions. June 15 gives us our earliest sunrise, at 4:57 AM, and the latest sunset comes on June 27, at 8:16 PM. Midway between these dates is the longest day of the year, on June 21.

It all has to do with the curvature of the earth and how the sun’s rays reach around the horizon. I don’t know enough about geometry to figure it out for myself, so I depend upon the U.S. Navel Observatory to provide me with a chart of sun times. If you want to find out what these times are for your location, go to their web site:

 http://aa.usno.navy.mil/data/docs/RS_OneYear.html

December 24, 2006

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