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StarDate: Summer Solstice— Plotting The Sun’s Motions

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FROM THE UNIVERSITY OF TEXAS McDONALD OBSERVATORY, AS HEARD ON KCBS RADIO WEEKDAYS @ 9:52 A.M., 7:35 P.M. & 2:52 A.M.

STARDATE 6/20/2014: Summer arrives tomorrow in the northern hemisphere, as the Sun stands farthest north for the entire year. It’s also the longest day of the year in the north, with at least 14 hours of daylight for everyone in the United States.

It’s not too surprising that the summer solstice has been an important day for almost every major civilization. Thousands of years ago, astronomers in Egypt and China could predict the solstice dates far in advance. And skywatchers in England built Stonehenge and many similar structures to help them predict and record solstices and other important astronomical dates.

Astronomers in the Americas built observatories, too — hundreds or even thousands of years before the first Europeans ventured across the Atlantic.

Perhaps the best example is El Caracol in the ancient Mayan city of Chichén Itzá. It was built around 1100 years ago, and was altered several times over the centuries.

El Caracol is a cylindrical tower that contains a series of tall, narrow windows. Priests used this structure to keep a close watch on the motions of the Sun, Moon, and the planet Venus. Two of its windows align with the sunrise and sunset points on the summer solstice.

This knowledge of the sky helped the Maya maintain both agricultural and religious calendars. It helped them know when to plant crops, when to sacrifice to the gods, and when to start wars — events regulated by the clock-like workings of the solar system.

Script by Damond Benningfield, Copyright 2014

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