Letter: Geocentric views in ancient Greece

From Mr Julian B. Barbour

Sir: W K Harper (letter, 27 January) is perpetuating an injustice by trying to prove the existence of a "golden heliocentric age" of Greek astronomy before Ptolemy put the clock back for 13 centuries. Mr Harper claims that Aristarchus asserted that the Sun is the centre of the solar system and that the planets revolve around it. He may have, but all the extant accounts of what he said merely mention the Earth. There is no word about the planets and not a shred of evidence that Aristarchus had Copernicus's great insight that mobility of the Earth can explain - at a stroke - all the retrogression loops of the planets.

The first really "professional" Greek astronomer (ie, someone who attempted to set up proper theories of the motions of the celestial bodies and test them by observations) was Hipparchus. His only great successor in antiquity - 300 years later -was Ptolemy. Both were geocentrists, but the outstanding lasting value of their work is quite independent of the geocentric-heliocentric issue.

It is not Ptolemy's fault that a few paranoid clerics and an especially vain pope at the height of the counter-reformation took a dislike to Galileo and tried to rescue the old Ptolemaic world view. Criticising Ptolemy for geocentricity is like blaming Newton for not having anticipated Einstein's relativity.

Yours etc.

Julian B. Barbour

Banbury, Oxfordshire

27 January