Under the Microscope/Prof William Reville: Astrology is the study of the motions and relative positions of the planets, sun and moon, interpreted in terms of their effects on human characteristics and activities.
Scientists in general, and astronomers in particular, will tell you that there is no scientific evidence for astrology. Nevertheless, astrology is quite popular.
It is said that 99 per cent of people know their sun sign, and, although most people go no further into astrology than occasionally reading the newspaper horoscope column, some people take the matter very seriously indeed.
It is said that former US president Ronald Reagan consulted astrologers before making important decisions.
Our calendar is based on the motion of the earth around the sun - one year equals one revolution. The sun appears, from the earth, in nearly the same position in the same zodiac sign on the same day each year. Astrologers believe that the sign the sun was in at the time of your birth indicates your basic nature and predisposes you to use certain strategies in dealing with life situations.
The zodiac is an imaginary belt in the sky extending eight degrees on either side of the ecliptic (great circle on the celestial sphere representing the apparent annual path of the sun relative to the stars), which contains the 12 zodiacal star constellations and within which the moon and planets appear to move.
The 12 signs of the zodiac and corresponding dates of birth are Aquarius (January 21st-February 19th), Pisces (February 20th-March 20th), Aries (March 21st-April 20th), Taurus (April 21st-May 20th), Gemini (May 21st-June 21st), Cancer (June 22nd-July 22nd), Leo (July 23rd-August 22nd), Virgo (August 23rd-September 22nd), Libra (September 23rd-October 22nd), Scorpio (October 23rd-November 22nd), Sagittarius (November 23rd-December 22nd) and Capricorn (December 23rd-January 20th).
Astrology has been practised for thousands of years. The Greeks developed most of the fundamental elements of modern astrology. The rise of Christianity curbed astrological practice, but it became popular again during the Renaissance. It remains popular to this day, despite the fact that its claims are fantastically improbable from a scientific point of view.
Astrologers base their predictions on the positions of the sun, moon and planets at the time of birth. But what is so special about the time of birth? Why are the forces that supposedly exert astrological effect not effective one month before the actual birth when a sentient viable being is present in the womb? And indeed, why the importance of the time of birth anyway - wouldn't the time of conception, when the whole process of formation of the new human being starts be a more likely focal point at which these astrological forces would exert their moulding influence?
And what are these astrological forces in any event? It is true that the sun, moon and planets exert gravitational and electromagnetic effects on the earth, but apart from the sun and moon, most planetary objects are so far away that any influence they might have on anything on our planet would be swamped by the influences of other things on earth. And there doesn't appear to be any natural explanation as to how the stars could directly affect a child at the time of birth.
Science cannot explain astrology, but does astrology work nevertheless? The great preponderance of scientific investigation indicates that astrology doesn't work. However, there is some small evidence that favours astrology. Michel Gauquelin, a French psychologist, compared large samples of sports champions and ordinary people and found a strong statistical correlation in favour of the "Mars Effect" - outstanding sportsmen and women are significantly more likely than other people to be born when Mars is just rising, or overhead. Others have repeated this work.
In another large study, Hans Eysenck, professor of psychology at London University, correlated star signs positively with personality traits. However, this study can be criticised on the basis that, since almost everybody knows their sun sign, many people unconsciously live up, to some extent, to their astrological personality type. Other workers studied children, who are less likely to know about astrology than adults, and found no correlation.
We must remember that establishing correlation does not establish a causal relationship. Someone once told me that, in Ireland, installed telephone capacity data between 1900 and 1950 correlated exactly with admissions to psychiatric hospitals. It is not at all surprising that, of all the billions of conceivable celestial motions, at least some are significantly correlated with human events or individual personality traits.
Astrology makes large claims that are extremely improbable from a scientific viewpoint. In order to take these claims seriously it would be necessary to have extraordinarily strong evidence. On the contrary, the evidence is very weak. In the absence of extraordinary evidence to support extraordinary claims, the only sensible course is to treat astrology as seriously as you would treat an amusing party game.
Why is astrology so enduringly popular? One reason is that it promises an insight into the future and this is appealing because we don't like the unpredictable. Flattery is another reason and personality profiles drawn by astrologers frequently use pleasing terms like sensitive, practical, pleasant, and so on. Also, a skilled astrologer will seem to be talking about one individually, which is flattering, even though the statements apply universally, eg "you feel a need for people to admire you". This is called the Barnum effect after the US showman PT Barnum, who coined the phrase, "Never give a sucker an even break".
William Reville is associate professor of biochemistry and director of microscopy at UCC