For the moon accomplishes her circuit in a month, waxing and waning and disappearing; the sun and the heavenly bodies whose course is of equal length, namely those called the 'Lightbearer' and Mercury, perform their revolution in a year; the Fiery star in double that period; the star of Jupiter in six years; and lastly the so called star of Saturn in a period two and a half times as long as the heavenly body next below it.