Sir: Tom Wilkie ("Journey to the beginning of time", 24 January) puts The Almagest of Ptolemy (2AD) as the beginning of the advance of astronomy, but it was in fact a retrograde step that began a 13th-century interlude from Greek science until the recovery of Copernicus and Galileo in the 15th century. This was because the Catholic Church adopted, and made into dogma, The Almagest, its Earth-centred solar system and "divine" universe, and all scientific progress was blocked in Christian Europe.
In 390BC, Heracleides suggested that Venus and Mercury may orbit the Sun; Democritus (c.380BC) described the Milky Way as being composed of stars, the Moon as being similar to the Earth and matter composed of atoms; Aristarchus of Samos (c.270BC) asserted that the Sun is the centre of the solar system and the planets revolve round it.
Aristarchus estimated the distance of the Sun from the Earth by observation of angles; Erastothenes of Cyrene (c.240BC) calculated the circumference of the Earth as 28,000 miles, and Hipparchus of Nicea (c.130BC) used a total eclipse of the Sun to determine correctly the distance and size of the Moon. Seleucus, about 190 BC, was the last Greek astronomer to teach a heliocentric theory of the solar-system.
W. K. Harper