Posted by: soniahs | January 17, 2011

Hey baby, what’s your sign?

Exciting breaking news! A Minnesota astronomer has announced that astrological signs are all a month off! And what’s with this new ’13th sign,’ Ophiuchus?

Well, it turns out that this news is not so new, after all. Astronomers have known about precession of the equinoxes since the time of the ancient Greeks, 2,100 years ago! Hardly breaking news.

Sorry, Slytherin fans: this serpent hasn't been promoted...

Precession is the motion of Earth’s axis of rotation with respect to the stars that’s noticeable on a timescale of decades (it moves through 1 cycle every 2,600 years). From Earth, the Sun appears to travel across the sky along a constant path across a background of constellations known as the Zodiac. Precession means that the apparent timing of the Sun’s travels seems to vary, as we observe it from Earth. The Sun’s path doesn’t change (and keep in mind that the Sun’s ‘path’ is an illusion of perspective from our position on Earth- we are traveling around the Sun, not the other way around).

The recent news has been about the fact that the timing of the ‘astrological calendar’ is wrong: the Sun is basically not ‘in’ the constellations when astrologers have been saying that they are. This is a phenomenon that’s been known for centuries! However, there are a few more things wrong with the astrological picture:

  • First, the division of the year into 12 equally-timed astrological signs is a matter of convenience. The Sun does not spend the same amount of time traversing the 12 Zodiacal signs (they’re widely-different in size).
  • Second, Ophiuchus, the ’13th sign,’ lies along the Zodiac, but was excluded from the count for some reason when the ancient Babylonians made the divisions. Why? Probably because it was easier for their calculations to divide the sky into 12 equal pieces.
  • Third, the constellations are an optical illusion, only visible from the vantage point of Earth. They’re made up of imaginary lines connecting star ‘groups’ that can be in reality thousands of light years apart.
  • Fourth, and most important: astrology does not work! The reason we can read a horoscope and later think ‘gee, that predicted event x so well’ is because of something called confirmation bias. Human memory is fallible, and after the fact we will selectively recall the few sentences of a horoscope that seem to ‘predict’ events that happened, and forget the many more ‘predictions’ that did not occur. Despite millennia of searching, we have not been able to identify any cosmic force that would cause the planets or stars to affect our individual lives. And multiple scientific studies have proven that horoscope charts are no more predictive of our personalities than statements chosen by random chance.

So the upshot is this: If you liked your ‘old’ sign, stick with it. Chances are, your horoscope based on that sign is just as accurate as the one from your ‘new’ sign. Meaning that it will predict your future no better than a set of sentences pulled randomly out of a hat.

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