We've moved to considering accuracy when the sun shines through a construction from the point where you started which was an observer looking out to the open sky with only hills as framing references. Nothing wrong with that but different considerations apply.
Can I go back to the open sky point and try to expand on what I mean by "accuracy" since it's not a very accurate word!
I'll use Ballochroy which is described here but it's really a general point.
http://www.megalithicsites.co.uk/Calendar4.html
Some have claimed that sites like Ballochroy were used to predict the summer solstice with the calendrical precision that we now take for granted. In other words, using Ballochroy they could tell the date we now call June 21st (say).
My point was that refraction means you cannot do this. Some years it might work and in others, because of refraction, you could get the date we now call June 22nd or 23rd. You can apply the same point to any so-called predictive sight line. So I have a problem with that line of argument.
However, and this is my main point, determining what we now call June 21st may not have been the point of the exercise.
If the point was to determine when the sun turned in the sky, then Ballochroy is accurate (when taken in the context of the conditions that applied at each annual observation).
If something had to be done by the community to mark that point, the observers could tell them the appropriate day. Perhaps the actual observation was just as an important part of the process as the activities which followed.
So, if these sites were used simply to observe when something happened in the sky, that's good enough for me.
And I don't need convincing about the alignment qualities of the different sites which usually come into these discusions. I bought that one a long time ago.
However, I do remain highly sceptical about those arguments which claim that monuments were used to determine events with an accuracy equal to that which developed with the growth of astronomical knowledge several millennia later. Especially when doing so involves sightings that can be affected by refraction.
And, talking of the sun, thats enough of this for the moment. I'm now going out to enjoy it!
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