(A separate study would be possible of astronomical sites in the medieval Greek world.)Chronologically, the Middle Ages are conventionally divided into an Early Medieval and a Later Medieval period.A chief marker of this division is the re-emergence of urban society in the 12th century, which was accompanied by several changes that transformed medieval astronomy.
In the past two decades, the picture of astronomy in medieval Europe has undergone fundamental changes.
Computus was a practical astronomy, concerned with reconciling the periods of the Sun and Moon—in other words ’the science of the numbering and division of time‘ (Grosseteste 1926: 213).
Specifically, computus addressed the practical problem of establishing a reliable and uniform method for computing the date of Easter and the other moveable feasts in the Christian calendar.
It is only in the later Middle Ages, with the recovery of Ptolemaic texts, that astronomy was transformed to integrate quantitative observations with quantitative predictions using trigonometrically computed tables derived from geometrical models.
It is useful to consider six distinct, yet interacting, astronomical traditions in the European Middle Ages: the arithmetical tradition of computus, concerned with determining the date of Easter in the context of the Julian calendar; the practical tradition within monastic communities of determining times of prayer by observing the stars and the Sun; the ancient Roman tradition of astronomy as one of the mathematical disciplines within the seven liberal arts; the ancient Greek tradition of predictive mathematical astronomy stemming from the work of Ptolemy; a practical concern with the annual motion of the Sun along the horizon for various purposes including the orientation of churches; and finally, the various techniques of astrological prognostication.
Until recently, it had been customary to skip from the Greek and Roman astronomy of late antiquity to its recovery in the 12th century through Arabic intermediaries.