* Astronomy

And the second pattern that the stones show is the movements of the moon. The orbit of the moon around the Earth is in a slightly different plane to that of the Earth around the sun and so if we look to the horizon for the positions of the rising or setting moon, we find that they move around as the year progresses.

The motions of the sun and moon go through a cycle - called the Metonic cycle - which takes 19 years before they return to the same relative position.
If we follow the rising and setting positions of the moon through one whole cycle, we find that there are extreme northerly and southerly positions. each of the points gradually moves to the extreme, stays there briefly and then turns back again. The extremes in the cycle are called the major and minor standstills.
And at the Clava Cairns, Doug has shown that these four standstills are marked by individual standing stones.
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