The very name of this large stone circle in County Donegal, northwest Ireland, is of astronomical interest because it suggests an association with the Celtic calendrical festival of Beltaine, or Bealltaine, which is associated with the mid-quarter day of May 6. A conspicuous alignment at the site backs up the idea of such an association. If one stands by the tallest stone in the circle, which is on the southwestern side, then one can see on the far side a distinctive triangular stone covered with several cup marks. This stone is aligned with a point on the horizon where the sun rises on May 6. As a consequence, the cup-marked stone is often dubbed the Beltane Stone.

This combination of a 5,000-year-old astronomical alignment and a more recent mythical tradition that may have given rise to the name, and their possible linkage through Celtic calendrical festivals, is an attractive possibility. However, we cannot be sure. Several other astronomical alignments have been postulated at the circle, showing that the Beltane alignment may not be the most convincing. For example, there is a small hill summit at the relevant point on the horizon, but a much more conspicuous hill, Bin-nion Hill, appears just to the left, where the sun rises on about May 21. The idea of a precise Celtic calendar and its linkage back to an earlier “mega-lithic” calendar is also problematic in a number of ways. The Beltane alignment at Beltany may, after all, just be a coincidence.

Nonetheless, cup-marked stones do seem to be associated with astronomical alignments elsewhere—for example, at the Scottish recumbent stone circles—so the idea may not be so far-fetched that this particular springtime sunrise alignment was significant, for some reason, back in the Neolithic.

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