So what's your sign, baby?

I got a question about this from one of my dearest friends, and so I’ll take a bit of time to answer it here. In the infamous words of Charlie Tolbert at UVa, “Astrology is bunk.”

That’s it. That’s the bottom line. But we’re good skeptics so we’ll delve a little deeper.

(First though, I should note, I just discovered that there is a whole Facebook page called “Astrology is bunk” for students who have had the honor of taking Tolbert’s class. I never did technically, but I was his TA, and enjoyed the class greatly!)

Astrology is essentially the idea that the alignment of the stars and planets when you were born have some kind of effect on your life. But there are some holes in this hypothesis. First of all, only 7 “planets” were known to the ancients: Sun, Moon, Mercury, Venus, Mars, Jupiter, and Saturn. Astrological forecasting took those into account, but not Uranus and Neptune, which were there, but simply undiscovered. Wouldn’t a good astrologer have realized that something was off, and maybe even predict the existence of those planets long before they were spotted with telescopes. And what about Pluto? It was a planet and now it’s not, how has that ever been worked in?

You think they'd find the gas giants...

Next, there is the question of how the celestial objects affect you. The nuclear forces work over too short of a range, and the electromagnetic force isn’t very useful over large distances as well. Plus, astronomical objects are pretty much neutral anyway. So that leaves us with gravity. I could go through the derivation to show you that the gravitational pull of you mom’s obstetrician is comparable to that of the largest planet of our solar system, Jupiter, but that’s already been done. Note that his or her presence is not included in astrological forecasting. After 4 centuries of study with telescopes, there is nothing special about the planets or stars that would make them seem to affect our lives, and gravity isn’t it.

The topic of the current kerfuffle are the zodiac constellations. Typical Western astrology splits up the human population into 12 “signs” based on the constellation in which the sun was when that person was born. Note that these are specifically the ancient Greek constellations, as if they hold any special knowledge or significance to mysticism. As any good Astro 101 student can tell you, the Earth goes through a process called precession, in which the axis of the Earth slowly moves around a circlethe sky in a 26,000 year cycle. Therefore, celestial north isn’t always at the star Polaris, and was indeed pointed near bright Vega some long time ago. When you map the sun’s position against the background stars, it will change over time! Astronomers have to constantly upgrade their coordinates to keep up, yet Western astrology pays no heed to this, and your newspaper horoscope has the birth range for if you were born thousands of years ago!

July 31 means I'm a Leo! And look, there's the Sun in Leo! Except, I'm not 2000 years old...

The position of the sun on my actual birthday.

Well, apparently an astronomer in Minnesota (eh?) pointed this out to a reporter, and it morphed somehow into this huge DEAL where everyone is trying to recalculate their sign. Or, in some cases, refusing to change because they are so attached to it. It’s okay. I’ve been there. Though I was never really convinced of astrology’s supposed predictive powers, I relished the idea of being lion-like. Grrr. But really, it’s just silliness. The Christian Science Monitor has a really good article about this silliness, and includes the dates and the “13th zodiac sign” Ophiuchus. As they point out, this is not news to anyone who knows their way around the sky.

Finally, one could point out that science has found weirder things than we can dream up in our imaginations. Even if the mechanism seems absolutely implausible, does it work? The data say No. In a review of some 500 studies done on astrology since the 1950s, astrology fails over and over and over again to predict anything about a person. (It is really fascinating and I encourage you to check out the above-linked pdf.) In fact, you could give a whole room of people the same newspaper style horoscope reading and have most of them tell you, “Oh yeah, this sounds like me!” because they are written so generally.

So not only is astrology implausible and incorrect, it just plain doesn’t work. Unfortunately, that’s not the message that came across through the twisted world of the media.

Finally, if astrology does nothing, then what is the harm in belief? Most of the time, nothing. But pseudo-scientific thinking seems to have a way of causing damage in any case, as is cataloged by Tim Farley’s “What’s the Harm” website. Go ahead, check out the astrology section. Sucks, doesn’t it?

A great reference on astrology is on Phil Plait’s original Bad Astronomy website. Also, check out his take on the matter on his blog. Thanks also to Tim Farley’s SkepSearch for weeding out the nonsense.

Shamelessly stolen from the Bad Astronomer...

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