Gallivan Center Sundial at the Solstice

July 10, 2006


Provided by: Kurt Fisher
Summary authors & editors: Kurt Fisher

The animation above shows the moment of the Sun's transit of the local summer solstice indicated on the dial plate at the base of 2 1/2 story tall sundial, located at the Gallivan Center Plaza in downtown Salt Lake City, Utah (111.8 west longitude). Astrometric solstice occurs when the Sun reaches an ecliptic longitude of 90 degrees - a point located in the constellation Taurus that marks the beginning of the summer season. When the Sun reaches this ecliptic position, a person on the Earth sees the Sun at its highest apparent local altitude. This ecliptic position of the Sun defines the Tropic of Cancer (23° 26' 22" north latitude) when it's projected onto the Earth's globe. At the instant of this year's astrometric solstice, on June 21, 2006 at 12:26 UT, the Sun was directly over western Africa on the border between Mauritania and Mali. Each geographic location on the Earth experiences its own local summer solstice at local apparent noon over the next 24 hours. The above photograph was taken seven hours later at the local Utah solstice at 19:28 UTC (1:28 MDT). Note that the angular size of the light gnomon is 1 deg, and the elapsed time of the animation is approximately 4 minutes.

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