funny you should mention the winter solstice, cos that's what the theory is ...
Cosgrove went out with a bunch of locals and claimed to find a carved stone at almost exactly the right place for the shadow to fall ...
There was a broken stone, visible but inaccessible, in the right spot during the 1970's, apparently, but I dunno if it's still there ...
Though I suspect that Mr Moses Cosgrove was stark raving bonkers, thus is highly likely to be bang on the money on the basic evidence, whilst getting the conclusion gloriously wrong ...
maybe
heh
RG