Science and Belief: Astrology

Most newspapers carry a column someplace, with this type of information:

Taurus (April 20-May 20) *** "Maintain a sense of humor and go with the flow. Look for a pleasant surprise among all the confusion."

The reference to Taurus is to the constellation of stars around the variable reddish star Algol, the bull's eye. It is slightly to the east of the Pleiades, the "seven sisters." If you are born within the time span given, this is your horoscope. There is nothing wrong with it (it's always a good idea to maintain a sense of humor and to look for pleasant surprises) except that the implication is that this advice follows from some deep knowledge about what the stars and planets are doing to your fate in life. Our diagnosis: pseudoscience ("pseudo", pronounced sue-dough, is Greek for "false") or “junk science”.

Who is to say that Astrology is all wrong? Has it not captured people's trust for thousands of years? Are we not spending a great deal of money and time on obtaining and studying horoscopes? Unfortunately, being popular or expensive is not a guarantee of value. Did not the great astronomer Johannes Kepler himself produce horoscopes? Well, yes. And his discoveries regarding the motions of the planets surely improved knowledge of astronomy and physics. Doing astronomy costs money, and he had to demonstrate to his prince that he was doing something with useful applications: “OK, Johannes, should I sign this deal?” “Well, it will help your treasury and the stars are very favorable.” Applied science? We think not. Maybe applied psychology.

Kepler was the last one of the great astronomers to get involved in this astrology business (and he had his doubts, expressed privately). Since the time of Newton, astrology is no longer considered a science. When Newton showed that the positions of the planets as seen against the stars are completely predictable from general laws it became evident that these positions could not carry any independent information of interest. Yet, the belief lingered that being born at a certain constellation of the solar system would help determine one's fate. The origins of such beliefs is obscure, but they hark back at least to Babylonian times.

Astrology began as a straightforward planting calendar for the emerging farming communities. During the course of a year, the Sun moves from one constellation of stars to the next, as we see it against a different galactic background when proceeding along Earth's orbit. So, at planting time in early spring, the Sun can be counted on to go into the constellation appropriate for planting. Of course, the stars surrounding the Sun cannot be seen, so the ancient astrologists guessed the Sun's position from observing the last visible stars that came up just before the Sun rose over the horizon (heliacal rising of the next constellation along the zodiac). They cross-checked their guess by noting the last stars setting, just before the Sun rose; these would be in the constellation opposite the one currently occupied by the Sun.

There are 12 constellations along the path of the Sun (called the "ecliptic"), and these 12 define the "zodiac", the zone where we find Sol, Luna, Venus, Mars, Jupiter and every other planet in the solar system, as well as (occasionally) the zodiacal lights which are a reflection of sunlight from dust in the main plane of the system. Once a month (roughly) the Sun leaves one constellation and move into the next. So, observing the Moon also helped fix the position of the Sun against the invisible stars around it, by remembering where it was a month earlier.

Now let's go back to ancient Babylonian time, even before the building of the hypothetical astrological observatory known as the Tower of Babel (which reached out to the stars and had a lot of visiting scientists speaking in different tongues). In early spring, when it was time to plough, Taurus the bull was "dying", that is, setting in the west in the early evening. Going east from the dying bull, we find the twins (Gemini, a couple of mythical heroes), then the crawfish (Cancer, found in the two rivers defining Mesopotamia) and then the regal Lion (Leo, the symbol of the ruler). The Lion, being 3 constellations over (90 degrees), will be moving into the zenith at that point in time, closely followed by the fertility goddess, announcing the imminent advent of spring (Virgo). In the mythology of the time, the Lion kills the Bull and this celestial sacrifice makes things ready for the new growth on Earth, under the guardianship of the goddess.

As Earth proceeds on its orbit, the Sun moves eastward through Taurus into Gemini. During spring equinox the Sun is in Taurus, and a few weeks later, Taurus precedes the Sun and rises just before it, at dawn. The Bull is "reborn" and we are (in that ancient period) in the middle of spring with the fertility goddess reigning high in the evening sky. Time to celebrate. (How about a dance around a Golden Bull?) We see that Taurus is the "anchor" of the progress of the year: the Sun is with it in spring, when things come alive. The other key constellations (90 degrees apart) are Lion, Scorpion and Aquarius, marking summer solstice, fall equinox and winter solstice, respectively, when the Sun occupies them.

Now it gets complicated. The position of the Sun at spring equinox is not strictly fixed to Taurus - it migrates all along the zodiac. Each year, the position is found 20 minutes ahead (westward) of where it was the previous time. This is called "precession", and we now know it is a result of the wobbling of Earth's axis. Precession does not make much difference in the career of an astrologist telling people when to plough or sow. Between apprentice sky-watcher to retiring wizard his determination will shift by half a day only, relative to true equinox. But over several hundred years the error adds up. That's why re-calibration is needed (such as may have been provided by ancient observatories, including Stonehenge).

In two-thousand years (and some) the crucial spring equinox position shifted from Taurus to the preceding constellation Aries, and this is when astronomy began to flourish. At that time, about 1500 BC, the key constellations were Aries, Cancer, Libra and Capricorn. We still name the turning points for the Sun as seen on Earth after Cancer and Capricorn ("Tropics" of Cancer and Capricorn) even though the Sun is no longer in these constellations when it turns. Also, even today, "first point of Aries" refers to spring equinox, although the Sun is no longer in Aries but has long moved on, through Pisces. It entered Pisces, in fact, at the time of Caesar, and this has helped make the "fish" a special symbol for the Christian era. In a few hundred years, the Sun will move out of Pisces into Aquarius, when looked at during spring equinox. This will begin the "Age of Aquarius." To astronomers, it will be a non-event. They don't care where the boundary between Pisces and Aquarius was defined; it was chosen dependent somewhat on custom.

The discovery of the "precession of the equinoxes" is usually credited to the Greek astronomer Hipparchus (fl. 146-127 B.C.), who found a shift of the position of the stars relative to vernal equinox, when making the first known star map and comparing his results with earlier work. It seems inconceivable, however, that the ancient Babylonian astrologists would have missed the fact that "the four corners" of the seasons keep moving relative to the stars. In fact, ancient mythology suggests that this knowledge existed well before the Greeks invented science.