 On the Reckoning of Time ( De temporum ratione ) included an introduction to the traditional ancient and medieval view of the cosmos , including an explanation of how the spherical earth influenced the changing length of daylight , of how the seasonal motion of the Sun and Moon influenced the changing appearance of the New Moon at evening twilight , and a quantitative relation between the changes of the tides at a given place and the daily motion of the moon . Since the focus of his book was the computus , Bede gave instructions for computing the date of Easter and the related time of the Easter Full Moon , for calculating the motion of the Sun and Moon through the zodiac , and for many other calculations related to the calendar . He gives some information about the months of the Anglo @-@ Saxon calendar in chapter XV . Any codex of Bede 's Easter cycle is normally found together with a codex of his " De Temporum Ratione " . 
