Sunday, October 5, 2008

The Sundials in the Yard

I love the time just before sunset here next to the Fox River. With the low sun angle, the grounds here just seem to glow with a spectacular golden light. But if you are paying attention, there are changes going on... The days are getting shorter as we move into fall, but what is really happening to us, living in the mid-northern latitudes, is that as we orbit the sun, the axis of rotation of the earth is slowly pointing away from the sun.

The most apparent affect of this, other than the shortening days, is that the sun appears to be moving southward. Check out the enclosed photos. The upper was taken just over 3 weeks ago on September 9th, the lower this afternoon on the 5th of October. Both were taken from exactly the same location at "magic time" when that golden glow enveloped us, and from my timings, the sun was within a half degree (the angle extended by the diameter of the sun or moon) in both exposures.

Readily observable is that the sun is moving south, about 13 degrees in those 3 weeks, from the solar calculator I found on the Internet. Also apparent is that the upper photo was taken about 6:30 and the lower at 5:40 to catch the sun at the same elevation. If I took another in a month or so at the same time as the upper exposure, I could likely catch star trails! Just another demonstration that observations of the everyday world can be astronomical in nature!

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