Oh, Lord, give me a sign!


george washington and astrological signsWhen the British colonies in America switched overnight from the Julian to the Gregorian calendar — during the lifetime of George Washington — eleven dates got skipped over. The ignorant masses rioted in the cities, demanding the return their lost eleven days of life.

Now a similar tidal wave of empty-headedness is washing over the blogosphere, triggered by a small article about an old and unimportant fact: Your familiar astrological sign actually has nothing to do with the position of the corresponding constellation at your birth.  (We would need to redefine the date-ranges of the signs if astronomical realism were wanted.)

Labels are important to people. George Washington never celebrated his birthday on the date that we do. Kal v’chomer, today’s Scorpios are not going to relabel themselves as something else.  Want to understand the difference between astronomers and astrologers?  Pluto used to be labeled a planet.

Now here’s what happened to those astrological signs:

Even assuming that people are so unscientific as to believe that the position of the stars (relative to the earth) at the time of their birth determines anything, the practice of astrology doesn’t reflect those positions correctly. This situation is nothing new; the signs used by astrologers haven’t been right for a couple of thousand years.

Nor is knowledge of the astrologers’ error new. I remember seeing it as a physics undergraduate in the 1970’s, and I think Sir Isaac Newton explained it thoroughly in the early 1600’s. Even Hipparchus (over 2,000 years ago) noticed the precession of the equinoxes, and understood that this was proof that the Earth (rather than the stars) was moving.

Let’s make it simple:

Think of a spinning dreidel. If the dreidel isn’t perfectly vertical, you will observe a double spin: (1) a fast spin about its axis of rotation, and (2) the slower twisting of its axis around a vertical line. (This motion is called precession.)  Put simply:  The handle of the dreidel doesn’t always point in the same direction.  Its tip is moving in a circle.  That’s precession.

The earth is just like that spinning dreidel. Its fast daily rotation makes the stars appear as if they are going around us. (When astrology was first formulated, people assumed that the distant stars lived on a hollow celestial sphere, with the earth at its center.)  Because the earth is spinning, our nearby sun also appears to go around the earth daily.

But the earth isn’t just spinning, the earth is also making an annual trip around the sun.  Because of this, the sun’s daily path across the sky crosses a different part of the celestial sphere at different times of the solar year. Sometimes sunrise goes through the constellation of Aries, sometimes through Scorpio, etc. The pattern seems to repeat each year, and is the basis for the astrological signs.

So much for the fast rotation of the dreidel. Now we come to the slow precession.  The earth’s axis of rotation is precessing all the way around once every 27,000 years. So the whole celestial sphere, carrying all the constellations, is changing its position slightly each year. If the astrologers divide the celestial sphere into twelve segments, we can divide 27,000 by 12 to show that the astrologers’ calendar gets off by one sign about every 2,120 years.

There are two astrology systems. The only one that would be affected by a sudden awareness of this old reality is the one that is not popular among Western astrologers. Called the ‘sidereal zodiac’, it has no steadfast correlation between its signs and the seasons, and has thirteen signs rather than twelve.

The popular system (called the ‘tropical zodiac’) is a total “fudge”, intended to enforce a correlation between its signs and the seasons of a solar year. It arbitrarily defines “Aries” as whatever position the sun rises at on the spring equinox (regardless of whether it’s actually rising in the constellation of Aries).

So if you’ve been enjoying the twelve-sign system, this “news” won’t affect you anyway.

So much ado about nothing.

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