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October 25, 2016

Cepheus, king of the legendary land of Ethiopia, had a problem. His wife, Cassiopeia, had bragged that she was the most beautiful woman of all. The sea nymphs were a bit miffed by that, so they convinced Poseidon to send a monster to avenge the slight. To save his country, Cepheus had his daughter, Andromeda, chained at the shore as a sacrifice. At the last minute, though, she was rescued by Perseus, who turned Cetus to stone by showing it the head of another monster, Medusa.

Most of the major players in that little drama are commemorated in the sky as constellations. And the tales of those constellations were handed down to us in one of the most important books in the history of astronomy.

The Almagest was written almost 2,000 years ago by Claudius Ptolemy, a scientist in the city of Alexandria. The book describes the motions of the Sun, Moon, and planets. It discusses eclipses and the length of the year. And it explains the cosmology of the time — the idea that Earth sat at the hub of a celestial sphere.

The book also includes a star catalog. Part of that catalog is a listing of 48 constellations visible in northern skies. Many of them had been around for millennia. But Ptolemy compiled them into a single convenient source.

All 48 of those constellations are still in use today — including Cepheus. It’s high in the north this evening, and looks like an upside-down version of a child’s drawing of a house.

More about Cepheus tomorrow.


Script by Damond Benningfield

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