What's Your Sign--Really

There is no factual basis to astrology, of course, but now a story over at LiveScience shows that there is even less reason to believe our astrological forecast: our "sign" may not be what we think it is.

Zodiac signs were originally determined by which constellation the Sun was "in" on the day you were born.

Early astronomers observed the Sun traveling through the signs of the Zodiac in the course of one year, spending about a month in each. Thus, they calculated that each constellation extends 30 degrees across the ecliptic.

But this was more than 2,200 years ago.

Unbeknownst to the ancient astrologers, the Earth continually wobbles around its axis in a 25,800-year cycle. This wobble—called precession—is caused by the gravitational attraction of the Moon on Earth's equatorial bulge.

Over the past two-and-a-half millennia, this wobble has caused the intersection point between the celestial equator and the ecliptic to move west along the ecliptic by 36 degrees, or almost exactly one-tenth of the way around. This means that the signs have slipped one-tenth—or almost one whole month—of the way around the sky to the west, relative to the stars beyond.

For instance, those born between March 21 and April 19 consider themselves to be Aries. Today, the Sun is no longer within the constellation of Aries during much of that period. From March 11 to April 18, the Sun is actually in the constellation of Pisces!

So if the predetermined characteristics of your sign never seemed to apply to you, now you know why. Or, more likely, it could be because there is no reason to think that the positions of stars millions or billions of light-years away should have any bearing on your psychological make up.