Most of Ælfric's description of the cosmos would be recognisable to any nakedeye observer of the heavens today. To make sense, however, of his explanations of the causes of celestial phenomena, we need to understand how he and his contemporaries conceived the universe. In essence, medieval cosmology continued to be based largely on the mixture of science and philosophy which constituted the teaching of Aristotle and his Greek successors; this was then filtered, in accordance with patristic tradition, through certain key scriptural passages held to give insight into the nature of the universe. Ælfric would have been familiar with the words of Ecclesiastes I.4–6:

There were inevitably tensions between the Greek and Hebrew cosmological traditions, and the problem of reconciling the celestial spheres of Greek cosmology with the heavens whose creation is described in the book of Genesis would become the subject of considerable debate in the later Middle Ages, when texts of the seminal works of Aristotle and Ptolemy had once again become available in the West. In late-tenth-century England, however, it was not possible to consult directly the works of Greek philosophers and astronomers, and Ælfric does not stop to discuss these issues in detail in DTA. Indeed, in places his account is not wholly illuminating. Writing of the events of the second day of Creation, he refers to ða oðre heofenan ðe bufon hire [sc. the firmament] sind 7 beneoðan, simply stating that they are ungesewenlice 7 mannum unasmeagendlice (17–19), and mentioning briefly two scriptural passages held to give authority for the belief in a multiplicity of heavens. The meaning of his reference to the heavens below the firmament he does not explain (but see Commentary, para. 6). Whatever Ælfric's conception, he may well have felt that to go into more detail would be tacitly to encourage the kind of fantastic speculation characteristic of contemporary apocryphal texts, such as the Visio Pauli, which he so clearly found distasteful.

A fundamental medieval principle is that the universe is constant and unvarying, at least until the cataclysmic events which will signal the coming of the last days.