There is one very simple answer that those who accept the principles of astrology give to sceptics who condemn it as a load of mumbo-jumbo: don't look at the stars for an explanation, go to the coast and look at the sea.
The massive power of waves and the tides that cause them are, it is universally accepted, a direct consequence of the gravitational influences of the Moon and the Sun upon Earth. We also know that the Moon sometimes determines animal behaviour and has long been linked with aspects of our lives as diverse as a women's menstrual cycle and mental disturbance, hence the word lunatic.
Is it, astrologists argue, therefore completely impossible that the other planets also exert influences on our lives and personalities, to greater or lesser degrees and in varying combinations? And that, having been around in various forms since the ancient Babylonians first began to describe celestial omens 4,000 years ago, astrology deserves more respect than the derision commonly accorded it by the rational scientists and the established churches.
Astrologists were forced on to the defensive once again yesterday after the publication of a German-Danish study of more than 15,000 people - the largest of its kind - which concluded "in no cases did date of birth relate to individual difference in personality or general intelligence". There was "no support" for a link between date of birth and the "Sun signs", the report said, and there was probably "more truth in a comic strip".
"It is the same old story" sighed Adam Fronteras, a former president of the British Astrological and Psychic Society (BAPS) and a regular broadcaster and writer on astrology and other psychic matters. "We've had these reports many times before. Because such research tests one or two factors only, it's a bit like judging a work of art using only one or two colours or a book by reading two pages. Astrology is much more complex than that."
Marlene Houghton, an astrologer for more than 30 years, puts it another way. "Astrology is a metaphysical doctrine, not a science, and cannot be easily judged by the narrow instrument that is science."
So what is astrology? It should never be confused with astronomy, the study of the planets and stars and whose practitioners, such as Sir Patrick Moore, are among the loudest critics of astrology. Astrology is seen by its advocates as a far more complex subject than the broad brush of the "Sun sign" astrology of newspaper columns and television pundits, where personality traits and predictive forecasts are ascribed to the 12 signs of the Zodiac in which people are born.
And it is not, stresses Christine Chalklin, the director of the Astrological School of the BAPS, a belief system. "I get very annoyed when people ask me why I believe in astrology," she said. "It is more like a language which is there to decipher and understand and to use during our lives. And it can have immense value."
Although there are many different sources of astrology, most modern Western "horoscopic" astrology dates from Hellenistic Egypt around 100BC and is different from, say, Hindu or Chinese astrology, although all share the same core practices.
Western astrologers base their study of a person on the calculation of their horoscope (a word derived from the ancient Greek) or "natal chart" - the positions of some of the planets, the Sun and the Moon - at the precise time of birth. These are plotted against the Zodiac (from the Greek word zoon, meaning animal), an imaginary belt in the heavens which includes the Sun's path (the ecliptic) and the apparent paths of the Moon, and the planets Mercury, Venus, Mars, Jupiter and Saturn. It is divided into 12 parts, each of 30 degrees and named according to one of the constellations - Aries, Taurus, etc.
The astrological year thus begins when the Sun moves into Aries on about 20 March and ends when it moves out of Pisces. …