The Problem with Astrology

I have recently been quite sick, and I've had a lot of time to catch up on my reading.  One of my current crusades is to go through one of my big undergrad astronomy / astrophysics books (Carroll and Ostlie's 1400 page magnum opus An Introduction to Modern Astrophysics, for the curious) and doing all of the proofs.  I don't get a chance to keep my mathematical skills up at work, and I'm still seriously considering a run at grad school sometime in the mid-future.

Perusing the introductory chapters reminded me of an old topic that has long amused me.  Even if astrologers are entirely correct, and the position of the stars affects our lives, they are wrong.  Why?  Because their horoscopes and birth charts have no relation to the actual position of the stars in the sky.

Take, for example, your "sun sign."  I was born on Aug 5, so mine is supposed to be Leo.  I ran a plot of the sky at the time of my birth in Starry Night (a well known and very accurate all-sky simulator) and I noted something curious.  Click on the image at right and have a look for yourself.

The Sun isn't in the constellation Leo at all.  It's in Cancer.  So I should be a Cancer, shouldn't I?  Why on Earth does this happen?

A little research found an excellent article by the astronomer John Mosley at the Griffith Observatory.  In it, he presents what anyone familiar with astronomy knows to be the reasons:

The idea that all constellations are the same size is not true.

First of all, not all of the constellations cross the ecliptic (the path of the Sun through the sky, shown as a green line on my plots) the same amount.  Scorpius is a tiny, narrow, constellation.  Pisces is a big fat one.  The Sun spends much more time in Pisces every year than it does in Scorpius, yet these "signs" are of equal size to astrologers.

The idea that there are twelve constellations of the zodiac is false.

The Sun passes through thirteen constellations every year.  Yes, that's right, there are 13 signs in the zodiac.  I plotted the stars and planets at Ben's birth (Dec 11) to prove my point (sorry, babe!).  Have a look at the image at right.  When Ben was born, the Sun was in the constellation Ophiuchus, not Sagittarius.

Mosley is quick to debunk the idea that this was caused by the International Astronomical Union's definitions of the boundaries of the 88 modern constellations in 1930.  No less an astronomer than Ptolemy published charts (in Almagest, circa 130 CE) which show four stars in Ophiuchus below the ecliptic (and thus crossing it, making Ophiuchus a part of the zodiac).  Wikipedia also claims that the foot of Ophiuchus crosses the ecliptic on the Farnese Atlas, a recently discovered Roman statue that depicts the sky according to the greatest of the Ancient Greek astronomers, Hipparchus.  That would mean that people have known that the Sun crosses into Ophiuchus since approximately 200 BCE.  (For those interested, the stars Ptolemy noted as below are 6 Oph, 42 Oph, 44 Oph and 51 Oph in Flamsteed's numbering system).

So congratulations to those born between Nov 30 and Dec 17 (give or take a day, depending on how you round your leap years).  Your sun sign is Ophiuchus.

The location of the Vernal Equinox is not constant.

The Vernal Equinox is the point where the Sun crosses the Earth's equator, heading for (celestial) North.  It corresponds to the day in the Spring (or Fall in the southern hemisphere) when day and night are of equal length.

When you think of the Earth in motion, you think of it spinning around the north pole.  You also think of it moving around the Sun in a nearly-circular orbit.  These are the two largest motions that occur.  However, the north pole also "wobbles" in a circle, in exactly the same way (and for exactly the same reasons) as a child's top when it slows down.  This causes the North pole to point to different places.  Right now, the star Polaris is closest to North.  In 13,000 years, it will be far from the closest.  This motion of the Earth is called precession.

The precession of the Earth's axis causes the stars to "drift" over time.  Most astrological calculations are now off by one constellation - some are off by two.

The planets pass through no less than 21 constellations.

Check out the planets at my birth above.  See Venus?  It's in Orion.  This is heresy to a traditional astrologer, as Orion is not a sign of their zodiac.  But there it is, plain as day.  Mosley and Jean Meeus calculated that the planets (not including Pluto) wander through 21 constellations over their orbits.  It's all well and good for Venus or Mars to be in a Fire sign, but what does it mean when Venus is in Orion?  Traditional astrology has no answer, and continues to pretend that the problem does not exist.

Conclusion

So we've shown here that one's "astrological" charts have nothing to do with the actual stars in the sky.  This is a recognized problem in astrology, and several practising astrologers now discount the old charts that are still used by the majority.  Dr. Shepard Simpson provides a page detailing the "real" zodiac and its astrological implications for those who still believe in the stars.  Other astrologers cling to the view that the "signs" and the constellations are different things.  If this is so, then what affects your behaviour and your destiny if it is not the stars

Obviously, I'm a non-believer.  But, for those who still think that there is something to all of this, I'm willing to make some concessions.

As shown in Mosley's paper, here are the actual "sun signs," circa 2000 CE:

Constellation	Dates (each side ±1 day, depending on leap years)
Capricornus	January 19 to February 15
Aquarius	February 16 to March 11
Pisces	March 12 to April 18
Aries	April 19 to May 13
Taurus	May 14 to June 19
Gemini	June 20 to July 20
Cancer	July 21 to August 9
Leo	August 10 to September 15
Virgo	September 16 to October 30
Libra	October 31 to November 22
Scorpius	November 23 to November 29
Ophiuchus	November 30 to December 17
Sagittarius	December 18 to January 18

Also, if you're interested in where the planets were when you were born, send me an email.  I'll run the computations and give you the facts.

Comments

[Todd]

Okay, this is awesome. It still baffles me that people believe in astrology, but it's even more funny now that it seems astrologers are all full of it even more than I thought.

[pamala merkel]

born 6-27-58 2:45 pm cancer? i am textbook cancer, read a cancer, thats me... show me my planets.
thanks
pamala

[isla]

my birthday is november 29th 1978 @ 3:52 Am.....
i want to know if i am a scorpio or an ophiuchus.....
also, what about all the other planets and rising sign...does everything get divided by 13???
is there a website that casts these NEW charts???
thankyou
isla