Great post, Tana.
In more recent times American astronomer Gerald Hawkins used a computer to decode many of the stone alignments and from this concluded that Stonehenge was a sophisticated means of observing the heavens. But it is doubtful if these early observations were precise or that the ancients were engaged in the same quest of discovery as scientists are today. Their most likely concerns would have been to establish a basic calendar and to chart the movements of the heavenly bodies for religious purposes.
I wondered about this.. might it have just have been for agricultural purposes? I suppose the better you can track the heavens, the more of an idea you know exactly what time of year it is, since they didn't have clocks and paper calendars to follow back then; and since there are usually some wild temperature fluctuations in the transitional seasons, that could lead to planning mistakes. I'm assuming it might have been difficult (otherwise) to know just when to start/stop planting, or reaping, and that knowledge was critical to survival.