Shifting Seasons

StarDate: March 7, 2009

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Spring arrives in the northern hemisphere in a couple of weeks. It's a season of birth and renewal -- a time of year that's associated with the constellation Aries, the ram. But it's an association that doesn't have the same snap as it did in ancient times.

Several thousand years ago, when the zodiac was first drawn, the Sun stood inside Aries at the time of the equinox. And today, the March equinox is still known as the "first point of Aries" -- even though the Sun now appears in Pisces on the equinox.

The change is the result of an effect known as precession. It's basically a "wobble" in Earth's rotation caused by the gravitational pull of the Sun and Moon. As a result of this wobble, the point of the equinox moves all the way around the sky. That means that as the centuries roll by, the Sun appears against different stars at the equinox.

It takes about 26,000 years to complete one full wobble. Since it's been several thousand years since the Sun last appeared in Aries at the equinox, the ram won't mark the equinox again for another 22,000 years.

For now, look for the ram descending the western sky during early evening. But you'll have to look long and hard, and have a good imagination, to "see" a ram in these stars. In fact, from most locations you probably won't see more than one or two of its stars, and even those will be faint. Its brightest star is modest, and shines with a subtle yellow glow.

Script by Damond Benningfield, Copyright 2009

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