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InvisibleDiploidM
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Astrology, Precession, And Pseudoscience: A Primmer
    #4137306 - 05/05/05 01:05 PM (11 years, 7 months ago)

I've been asked by a few people here to give an explanation of why a property of the Earth's orbit called precession invalidates astrology. Well, here it is:

First some terminology and basic principles of astronomy.

1. Angular measurements are made using degrees. There are 360 degrees in a full circle. Fractions of degrees are measured in minutes and seconds, so 1.5 degrees is the same as 1 degree, 30 minutes, 0 seconds.

2. The path of the sun against the backdrop of (essentially) fixed stars is called the ecliptic. Which constellation the sun is in on the ecliptic on your birthday is what determines your sign.

3. The position of a star in the sky is defined by its Right Ascension (RA) and it's Declination (Dec). This is analogous to latitude and longitude on a land map. RA is given in hours, minutes and seconds, Declination in degrees, minutes and seconds.

4. The Celestial Sphere is an imaginary sphere surrounding the Earth with its poles exactly aligned with the poles of the Earth. The celestial sphere rotates once a day around the celestial poles as a result of the rotation of the Earth on its axis. All astronomical objects can be considered as lying on the celestial sphere.

5. The zodiac consists of 12 even slices of the ecliptic, one for each sign, so each sign subtends 30 degrees in the sky (360 / 12).

6. An astronoMer is a scientist. An astroloGer is a mystic.

Now the beef.

The Precession of the Equinoxes, also known by the name Precession of the Zodiac, is a gradual westward movement of the zodiac on the celestial sphere. Its main component, caused by the gravitational pulls of the Sun and Moon on the Earth's equatorial bulge, is known as Lunisolar Precession. An additional effect due to the pulls of the planets is called Planetary Precession. The sum of these two components is called General Precession.

Precession causes all the stars to slowly move west parallel to the ecliptic such that the stars visible from any given place and time of night gradually changes throughout one cycle of precession. Because of precession, the right ascension and declination of stars are continually changing. The total change amounts to ~ 1.5 degrees per century.

To allow for this constant change, and because it would be too expensive to issue new star charts every year, star charts give star coordinates for a standard epoch, which by international agreement is currently the start of the year 2000. On January 2, 2000, all the star charts are in error because of precession, but the effect is small enough (only 1.5 degree per century) that it is only corrected at each new epoch, typically every 50 years.

However, over the course of the 2000+ years since astrology was invented, precession has drifted the celestial sphere by about 30 degrees, or one entire sign. Professional astronomers compensate by issuing new tables at each epoch, but astrologers stuck in 2000 year old pseudo-science do not.

A concrete example:

The star Beta Capricorni is currently at position 20 hours, 21.0 minutes RA and -14 degrees 46.9 minutes Dec. If you point a telescope at that spot, you will find Beta Capricorni. In 100 years, you will be off by 1.5 degrees, and 2000 years ago, you would have been in error by 30 degrees ( 1.5 * (2000 / 100) ), or one complete sign.

This is why if you think you're any given sign, you are actually one sign over. Most astrologers are ignorant of these facts because all they do is plug your birthday into a computer program and 'interpret' what comes out. The ones that do know about precession never mention it because it would wreck their money-making system. Both types of astrologers count on their blind followers to never look this stuff up for themselves.

Source: Norton's 2000.0 Star Atlas And Reference Handbook, Eighteenth Edition


--------------------
Republican Values:

1) You can't get married to your spouse who is the same sex as you.
2) You can't have an abortion no matter how much you don't want a child.
3) You can't have a certain plant in your possession or you'll get locked up with a rapist and a murderer.

4) We need a smaller, less-intrusive government.


Edited by Diploid (05/06/05 12:24 PM)


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OfflinePhluck
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Re: Astrology, Precession, And Pseudoscience: A Primmer [Re: Diploid]
    #4138301 - 05/05/05 05:03 PM (11 years, 7 months ago)

Well, if I didn't think astrology was completely bunk, I'd say that the stars are still accurate because they're magic.

However, that would account for the various studies done that found no correlation between star signs and personality traits.

http://www.skepsis.no/english/subject/astrology/studies.html

Note the abundance of studies finding no correlation, and for the few studies that do, they're followed by studies attempting, and failing to replicate the successful studies.


--------------------
"I have no valid complaint against hustlers. No rational bitch. But the act of selling is repulsive to me. I harbor a secret urge to whack a salesman in the face, crack his teeth and put red bumps around his eyes." -Hunter S Thompson
http://phluck.is-after.us


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