Dramatic entry of the sun near the summer solstice. Picture taken in 1997.
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The entrance of Cairn G incorporates a structure known as a roofbox. The only other example currently known in Ireland is the famous Newgrange example which is aligned to the winter solstice sunrise. Another was found last year at Crantit on the Orkney Islands which have abour 80 chambered cairns. The Carrowkeel example has several features in common with the one at Newgrange. It is located over the entrance to the chamber; a stone door is present; and the roofbox admits a beam of light from the sun at sunset over midsummer. However, there are also several features about Cairn G which are different to Newgrange. The passage is much shorter than Newgrange, only about two meters long, and so the roof box opens directly into the chamber. This means that the sun can shine into the chamber for a much longer period of time than Newgrange - approximately a month on either side of midsummer, though it only spends about two weeks in the rear of the chamber. Also, even though the sun has been displaced by 1.5 degrees (three solar diameters) to the west, it is impossible for the midsummer sunset to have shone into the end recess of Cairn G. In the photograph below, the sunbeam is shown in its maximum position, centered over the left recess, and this is probably pretty much as it was in ancient times.
But what about the moon, which seems to get overlooked in preferance to the sun, for example at Newgrange. The full moons rise and set approximately 180 degrees opposite the sun's rising and setting positions. The setting full moons on either side of the winter solstice will illuminate the chamber of Cairn G in much the same fashion as the sun does each summer. After having figured this out a few years ago, I have endevoured to check it out, but for the last two years the moon has set in to thick banks of cloud over the Ox Mountains.
Bone pin from Cairn G (not to scale). |
Aerial view of the main group of cairns at Carrowkeel.
