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Moon and Aldebaran

August 24, 2016

The Moon slides toward the eye of the bull early tomorrow. In fact, it’ll pass directly in front of the star for a while — but not until the middle of the day for those of us in the U.S. We’ll have to be content with a beautiful close encounter in the wee hours before daylight.

A similar encounter more than 1500 years ago helped prove that the stars move across the sky — sort of.

In the early 18th century, British astronomer Edmund Halley compared the positions of three stars to their positions almost 2,000 years earlier. The stars were Sirius, Arcturus, and Aldebaran — the star the Moon cozies up to early tomorrow. He also used Aldebaran’s position during a similar encounter with the Moon in the year 509.

Halley’s calculations showed that all three stars had moved a significant amount in that time — the width of the Moon or more. It was a crucial discovery, because it showed that the stars aren’t “fixed” in space — they move. Halley also suggested that because the three stars moved so far across the sky, they must be fairly close.

Modern calculations show that Halley’s numbers for Sirius and Arcturus were spot on. But his numbers for Aldebaran were off — it hadn’t moved nearly as much as he wrote. Even so, the bull’s eye does move across the sky — just like every other star.

Look for Aldebaran to the lower left of the Moon as they climb into good view by 1 or 2 in the morning. The Moon will move even closer to it by dawn.


Script by Damond Benningfield

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