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May 11, 2015

Much of what we know about ancient astronomy was passed down to us in a single book, known as the Almagest.

It was written about 1900 years ago by Claudius Ptolemy, a Greek astronomer, mathematician, and poet. It recorded the cosmology of Aristotle, which taught that Earth was at the center of a perfectly spherical universe. It explained the motions of the Sun, Moon, and planets. And it introduced a scale for measuring the relative brightness of stars that’s still in use today.

The Almagest also passed along 48 constellations from ancient Babylonia and Greece. Those, too, are still around. In fact, without Ptolemy, many of those star pictures might have disappeared.

The list includes Hercules, the strongman. It’s low in the east-northeast at nightfall, and soars high across the sky later on. It’s marked by a lopsided square of stars known as the Keystone. None of the stars of Hercules is all that bright, though, so the strongman is best viewed on Moon-less evenings — like tonight.

Hercules and the other constellations of the Almagest were simple connect-the-dots pictures. Almost a century ago, though, professional astronomers expanded them. So today, each constellation is a well-defined plot on the sky, and encompasses everything within its borders — not just stars, but star clusters, galaxies, and everything else.

In Hercules, one of those objects is a cluster of hundreds of thousands of stars. More about that tomorrow.


Script by Damond Benningfield, Copyright 2015

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