Moon and Jupiter

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The Moon will be a pretty sight tonight. It's a little past first quarter, so the Sun illuminates a little more than half of the lunar hemisphere that faces our way. And it's especially eye-catching tonight, because it pairs up with Jupiter. The planet looks like a brilliant cream-colored star to the left of the Moon.

It's appropriate to watch the Moon today because it's the Moon's day -- Monday.

The seven-day week comes to us from the astrologers of Babylon, about 2700 years ago. They based the week on the seven known "planets" -- the objects that moved across the background of stars. The list included five real planets, plus the Sun and Moon.

The astrologers assigned one planet to each of the 24 hours of the day. In time, each day came to be known by the planet that ruled the first hour of the day -- the Sun, Moon, and so on. Jupiter's day is Thursday, which comes from Thor, the Anglo-Saxon name for the planet.

A thousand years after the Babylonians created the seven-day week, the Roman emperor Constantine formalized it, beginning with Sunday and followed by Monday.

Incidentally, the name for the Moon in many cultures is based on the Latin name luna. But the English words moon, Monday, and month come from Anglo-Saxon -- the language of the people who brought the seven-day week to Britain -- including what is now the least popular day of all, Moon-day.

More about the Moon and Jupiter tomorrow.

Script by Damond Benningfield, Copyright 2005, 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.