Evidence has also been gathered for lunar and planetary orientations of architecture. The moon is the second most luminous orb in the sky. Its appearance is commonly used to subdivide the year into convenient and easily observed units. For both megalithic sites, and the American southwest, statistical cases have been put forward for interest in the extreme setting points of the moon (this position varies with an 18 year cycle). While formally significant these cases lack a simple practical motive for cultural interest in such complex behavior. Planetary alignments have been found at Maya sites with readable inscriptions. The orientation of an individual structure (covered with Venus glyphs) to an extreme rising point of Venus is easily accepted, but without the tremendous body of supporting non-archaeological data for Maya interest in Venus, this orientation would remain an astronomical oddity.
Turning from architecture, a well known example of a possibly astronomical image is the petroglyph showing what appears to be a crescent moon and with a large spot nearby. The organization of the two elements is consistent with it being a relatively realistic representation of the 1054 supernova. Visible in the daytime sky, this object was certain to be of interest to anyone familiar with the sky. The uncertainty of date and local uniqueness make it difficult to prove this interpretation. A few years back, Bob Robbins suggested that the image on some Mogollon pottery (a rabbit with a large rayed spot) also represented the supernova. In this case, standard archaeological methods assure the date to be consistent, but it requires accepting a rabbit representation for the moon.
It is relatively easy to argue that people watched obvious phenomena with practical utility, like solstices. Claims for non-solar alignments, without a strong practical motivation, must at least make statistically significant cases. When combined with other data, they can also contribute to a circumstantial case for a more general astronomical interest; what might be called in legal circles a pattern of behavior. To the extent that such hypotheses help organize archaeological data and suggest additional research, they contribute to the discipline. If successful, such hypotheses can move archaeological understanding beyond what was done, to a piece of the why.
What reasons do you think caused prehistoric populations to develop calendars?
Anticipation! Even with all of the buffering offered by modern urban society, the cycle of seasons cannot be ignored. Hunters prosper if they anticipate the arrival of migratory game or fish, to prepare nets or blinds. Farmers want all possible precision for planting. More sophisticated farmers, who use irrigation, may be able to plant early and obtain an extra crop, if they know the seasons well enough. It is beneficial for any group to know how long it will be until more food resources become available. With the ability to anticipate the seasonal cycle, a group is more efficient (can support higher population), and is less at risk.
While calendrics are a particularly well motivated reason for studying the sky, it has been watched for other information. It provides guidance to nomads and sailors, particularly those traveling into new areas with few landmarks. It provides a clock to measure the day. A hunter who is familiar with the sky can look at the stars and know when he must leave home for a dawn arrival at his hunting location.
In historic times we know that people have looked to the sky searching for other information (the fate of kingdoms, earthquakes, health ...). While modern science provides little reason to believe the sky has any affect in these areas, value was perceived. It is not unreasonable to think that such interests existed prehistorically, just difficult to know.
