Astrology - is there anything to it?

Anyone who has studied astronomy at even the most elementary level understands can see that the claims of astrology are untenable. Why? Because we know that we are only a small speck in a universe that's incomprehensibly large and old. The possibility that the stars and planets can have some special effect on our lives outside of the known laws of physics is improbable, to say the least. And even though the daily horoscope on one's favourite website or newspaper might be an amusing daily distraction, plenty of people take astrology seriously enough to spend sigificant amounts of time and money on it.

So just what is astrology? Astrology claims that the position of the sun and planets in relation to the zodiacal constellations (see below) at the time of our birth has a profound influence on our personality and destiny (for the purpose of this discussion I'm referring to "western" astrology, but the same principles apply to Chinese, Indian, Aztec and other variants). We'll take a look at the main, obvious evidence against this, and also why it's still around.

But first: a little astronomy :)

What are constellations? These are groups of stars that resemble terrestrial artifacts, mythological characters or animals. There are 88 recognized by the International Astronomical Union, details here. Some of these shapes take a little imagination to see, others are a bit more obvious. To the ancients, one group of stars looked vaguely like a lion, another a goat, and yet another a scorpion. We humans projected our bronze age world onto the stars, as did the 17th century explorers when they saw the southern hemisphere constellations for the first time. They saw ships prows, telescopes and crosses in the sky. The constellations in the sky are in fact paredolian artifacts.

But they're not fixed. Nothing in the sky is. It's just that our lives are too short to notice movements that take place over hundreds of thousands of years. In all of recorded history the skies haven't changed significantly. We don't notice that the pole star is gradually drifting away from celestial north and that in the future, various other candidates will take its place. In a few hundred thousand years, the constellations we look at will have changed beyond all recognition due to stellar migration. Those that concern us for the present discussion are the zodiacal constellations, those that are grouped on the ecliptic - the imaginary line traced by the sun's annual apparent path in the sky.

So how do the planets come in to all this? The planets move around the sun in fixed orbits. As they do, we see them move "in" and "out" of constellations in the background. This is what astrologers mean when they say, for example, that Jupiter is in Leo: the planet Jupiter, in it's journey around the sun as seen from our perspective, passes in front of the constellation Leo. Of course, Jupiter is a lot closer than any of the stars in Leo, and Leo itself is just an arbitrary collection of stars at various distances from us and each other. We know, thanks to Kepler and Newton, exactly where all the planets are are now, where they were in the past, and where they will be in the future. We also know that when a planet appears to move backwards in its orbit (in retrograde) that it's simply because the Earth's orbit is overtaking that of the planet in question. Here's a good visual explanation for how this works in the case of Mars.

By what mechanism could the planets and stars affect us at our birth? Physics tells us there are only four fundamental forces in the universe. The strong nuclear force, the weak nuclear force, gravity and electromagnetism. The first two can be eliminated as they concern only atomic nuclei. EM is plausible only if the baby is born outdoors, and even then the light from the planets takes a certain amount of time to get to the earth. So should that be part of the calculation? And what about gravity? Its effect is inversely proportional to the square of the distance between the two bodies (F=G (mm')/r² if you remember your high school physics classes) so the gravitational force of the baby's mother would be millions of times stronger than our closest celestial neighbour, the moon, never mind any other celestial bodies. To paraphrase Carl Sagan, the moon is more massive, but mommy is closer.

Another problem:
Due to precession of the equinoxes the sun doesn't "pass" through these constellations on the dates proposed by astrology proponents. Here are the dates that are commonly accepted as being the "sign" of a person born in that interval (when the sun's apparent movement takes it through the the zodiacal constellations), as compared to when the sun actually crosses these constellations:

Sign	Sun's actual passage through constellation	Commonly accepted Astrological solar passage through constellation
Capricorn	Jan 20 to Feb 16	December 23 - January 20
Aquarius	Feb 16 to Mar 11	January 21 - February 19
Pisces	Mar 11 to Apr 18	February 20- March 20
Aries	Apr 18 to May 13	March 21 - April 20
Taurus	May 13 to Jun 21	April 21 - May 21
Gemini	Jun 21 to Jul 20	May 22 - June 21
Cancer	Jul 20 to Aug 10	June 22 - July 22
Leo	Aug 10 to Sep 16	July 23 -August 21
Virgo	Sep 16 to Oct 30	August 22 - September 23
Libra	Oct 30 to Nov 23	September 24 - October 23
Scorpius	Nov 23 to Nov 29	October 24 - November 22
Ophiuchus	Nov 29 to Dec 17	?
Sagittarius	Dec 17 to Jan 20	November 23 - December 22

A related problem, as evidenced by the table above: The zodiacal constellations aren't spread neatly and evenly across the sky. For convenience, most astrologers use twelve virtual constellations that divide the zodiac into neat, thirty degree regions and work from this instead of using the visible night sky. For example, the sun takes more than twice as long to pass through Virgo (44 days) as it does Cancer (21 days), yet astrology counts them equally, as per column 2 above.

Looking at the table again, you'll see a thirteenth constellation that's rarely mentioned: Ophiuchus. Now why don't we see this in the daily horoscopes? How many people have you met that say "Hi I'm an Ophiuchus, what's your sign?" ? Logically there should be as many Ophiuchuses (Ophiuchi?) as Leos or Capricorns. But there aren't. There are some astrological systems that use the constellations as they appear in the sky, but are in the minority. This detail aside, however, the fundamental theory of all astrology is the same: celestial bodies influence our destiny.

One obvious test of astrology is fraternal twins (to eliminate any possible genetic factors): If astrology were valid, they should have similar lives as they were born under similar circumstances. Time and again we see that this is not the case.

So given that we have this evidence against astrology (and there's plenty more where that came from), why does it persist into the 21st century?

We can boil it down to two principle reasons:

• A fundamental lack of critical thinking skills;
  
• General scientific illiteracy\apathy and a lack of curiosity in how the world works.

Both of these are essential to understanding why astrology, like other pseudosciences, persist into our technological age. These problems can ultimately be addressed by teaching critical thinking skills at both high school and university level (using, for example The Baloney Detection Kit *), and by using creative outreach programs that engage the public at large. As regards the latter, CatherineQ recently wrote a wonderful piece on why engaging people's emotions in popularising science is essential.

In the end, we may think of astrology as a quaint, quirky holdover from the past, and so adopt a "what's the harm" attitude.

At first glance there is no real danger in letting people pursue beliefs that may cost them a little money but are otherwise harmless.Yet there is real harm here. Astrology, like homeopathy and other pseudosciences, promotes magical thinking. No evidence or thought is required. It leads us to take the word of anyone who comes along with a magic solution to any and all problems. And when magical thinking gets together with health care or politics, the results can be disastrous, much more than merely financial. Would you like your leaders making policy based in part on astrological advice?

*Taken from THE reference on critical thinking and skepticism, Carl Sagan's The Demon Haunted World . If you haven't yet read it, it's a lifechanger.

Posted via email from John's posterous