If you were born in early December, your astrological "sign" is Sagittarius, the archer. But contrary to what you might think, the Sun didn't appear against the stars of Sagittarius at the time you were born. Instead, it appeared against the thirteenth constellation of the zodiac: Ophiuchus, the serpent bearer. The difference illustrates how the Sun's path across the sky changes over the centuries.
The zodiac was first outlined about 3,000 years ago. It was split into 12 equal constellations, with the Sun spending 30 or 31 days in each.
But in the 1930s, astronomers drew boundaries for the astronomical constellations. The constellations are different sizes, so the Sun spends varying amounts of time inside the borders of each one.
More important, the Sun moves westward across the zodiac over time -- an effect called precession. It moves roughly one constellation every couple of thousand years. So today, the Sun passes through each astronomical constellation about a month later than it enters the astrological one. And the Sun's path across the stars has moved enough that it now passes through Ophiuchus. In fact, the Sun spends more time in Ophiuchus than in neighboring Scorpius.
The Sun is passing across the southern edge of Ophiuchus. But the constellation is so large that many of its stars are still in view at nightfall. They're low in the west, spreading out to the right of the brilliant planets Venus and Jupiter.
Script by Damond Benningfield, Copyright 2005, 2008
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
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