In his On the Reckoning of Time Bede was the first northern scholar to explain how to predict the phases of the moon and its position in relation to theconstellations. in the zodiac.

Should someone rather less skilled in calculation . . . be curious about the course of the Moon, we have also for his sake devised a formula adapted to the capacity of his intelligence, so that he might find what he seeks. Thus we have marked out each day of the twelve-month annual circuit in the calendar by means of alphabets, so that the first and second alphabetical sequences each comprise 27 days, while the third sequence has one day more, namely the day which accrues from three repetitions of the eight superfluous hours. . . .

So if you wish to know what sign or what part of the month...