Ballochroy Standing Stones
Ballochroy Standing Stones in Kintyre is a Megalithic site of 3 Mica Schist stones ranging in height from 6 ft 7 in, 9 ft 10 in to 11 ft 6 in with the smallest possibly haven been broken at some point. The site was examined by Alexander Thom who worked on Stonehenge, and conducted scientific measurements of the alignment of the setting sun at Mid Summer and Winter Solstice against the Paps of Jura which suggests the site to have been from around 1800 BC.
The following information is taken from http://what-when-how.com/ancient-astronomy/ballochroy/
‘Ballochroy encapsulates Thom’s idea that prehistoric Britons used features on distant horizons as astronomical foresights in order to observe and record the motions of the sun and moon to remarkable precision. The central stone at Ballochroy has a broad, flat face oriented across the alignment that points northwest, directly at the slopes of Corra Bheinn, a mountain on the Island of Jura some 31 kilometers (19 miles) away. On the summer solstice, the tip of the sun’s disc twinkled down the indicated slope; a couple days before or after, when the sun’s path was just slightly lower, it would not have been visible. The row of three stones itself points southwestward toward a small island called Cara Island about 12 kilometers (7 miles) away. Close to the winter solstice, the tip of the sun’s disc gleamed to the right of the island as it set; on the solstice itself this would not have been the case.
The best evidence supporting the theory that Ballochroy was a “solar observatory” is that there are not one but two foresights at the same site, marking the setting sun at both of the solstices. Surely such a coincidence could not have arisen by chance? And yet many critics raised doubts. One of the other standing stones in the row also has a broad, flat face pointing northwestwards, but this one points at a different mountain. And the alignment along the row is very broad, encompassing not only the right-hand end of Cara Island but also its left-hand end and central peak as well. If we are fair with the data, then we should admit the existence of at least a few other candidates for foresights that are equally plausible but have no ready astronomical explanation.’