 The theory of trepidation is presented by Theon as an alternative to precession.Various assertions have been made that other cultures discovered precession independently of Hipparchus.According to Al-Battani, the Chaldean astronomers had distinguished the tropical and sidereal year so that by approximately 330 BC, they would have been in a position to describe precession, if inaccurately, but such claims generally are regarded as unsupported.