I think this idea has been mooted in one form or another before, but not necessarily so succintly. Can't remember where I read it, but someone once proposed that Callanish was used in this way. When the moon appears in its position at the head of the circle at the time of its maximum a priest could stand there (outlined by the moon as demonstrated by Julian in the TMA TV program) and tell it to 'stop and turn back', which of course it does very dutifully.

The same could be said of the sun entring chambers at the solstices. However, the idea does not explain equinoctal alignments.