Archaeoastronomy (also spelled Archeoastronomy) is, as the name implies, the combination of astronomical and archaeological studies. Specifically, it covers the intersection between the two. One aspect of this is the use of the historical record prior to the genesis of the modern astronomical discipline in order to study past astronomical events. It also may involve the use of astronomical knowledge and extrapolation to further our understanding of the historical record. The two disciplines interact constructively.
An example of the first sort of archaeoastronomy is the study of the extensive records of ancient China for references to "guest stars". "Guest stars," or star-like objects which appeared in the night sky, were of great interest to the observers of ancient China and were often dutifully recorded. These events have been associated with many transitory phenomena, such as comets and, particularly, supernovae.
An example of the second sort of archeoastronomy is the study of solar, lunar, and stellar alignments of historical monuments. Many claims have been made that the megalithic monument, Stonehenge, represents an "ancient observatory," although the extent of its use in that regard is in dispute. Certainly Stonehenge - and many other ancient monuments - is aligned with particular significance to the solstice and equinox points. Similar claims have been made that the Great Pyramids of Egypt are aligned with the stars in the belt of Orion, in reflection of the significance invested in that constellation by the ancient Egyptians.