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Clockwork Eclipses

May 17, 2012

A solar eclipse is coming up on Sunday afternoon and evening for most of us in the United States. Most will see a partial eclipse, with the Moon covering up only a portion of the Sun’s disk. But across a 200-mile-wide path from California to Texas, the Moon will fit inside the solar disk, surrounding the dark Moon with a ring of fire — a configuration known as an annular eclipse.

The timing of the eclipse is known down to the second. In fact, the motions of Earth, Moon, and Sun are so well understood that astronomers have already prepared equally precise timings of eclipses that won’t take place for centuries.

Such precise timing hasn’t always been the case, though. In fact, an eclipse forecast made 250 years ago helped turn a French astronomer into the toast of French science and society.

Madame Nicole-Reine Lepaute was the court astronomer to King Louis XV. In 1762, she wrote a paper predicting the circumstances of an eclipse that would be visible from Paris two years later. Her predictions were right on target.

Her husband, the king’s clockmaker, built a special clock to celebrate her accomplishment. It included a diagram of the eclipse from her paper, plus a small figure of Urania, the muse of astronomy.

The clock is still around today — not in Paris, but on the campus of the University of Arizona — marking the never-ending motions of Earth around the Sun.

We’ll have more about Sunday’s eclipse tomorrow.


Script by Damond Benningfield, Copyright 2012


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