Archaeo-optic observations at Carrowkeel, County Sligo, Ireland

Other than Newgrange, Carrowkeel Cairn G is the only Neolithic cairn known to feature a second opening above the passage entrance, known as a roof-box. The roof-box enables light to reach the chamber, even when the entrance to the passage was closed.

Carrowkeel Cairn G, with neighboring monuments in the background (Photo: Aaron Watson)

In the present day the entrance into Cairn G is largely blocked by rubble (Photo: Aaron Watson)

The narrow opening above the passage entrance described as a 'roof-box' (Photo: Aaron Watson)

Looking down the passage into the chamber (Photo: Aaron Watson)

Looking from the chamber towards the entrance. Although a stone slab used to block the entrance is in place the roof-box above allows light to enter (Photo: Aaron Watson)

While Newgrange is aligned upon the midwinter sunrise, Carrowkeel Cairn G opens towards the midsummer sunset. This has lots of interesting possibilities for archaeo-optic observations, but on this rather overcast day in October I was working with reflected light.

The roof-box offers a means of controlling how light enters the cairn. At Newgrange this appears to have been done using blocks of stone in the Neolithic, but for my observations at Carrowkeel I used a sheet of fabric punctured with a small hole.

The aperture in place within the roof-box (Photo: Aaron Watson)

Similar to my observations at several chambered cairns in Wales and Scotland, it was possible to project images of the outside world upon the chamber walls. In Carrowkeel Cairn G the complex architecture presented a number of different screens upon which the inverted image of a human figure can appear as they move around outside the monument.

Animated sequence of still photographs showing the projection of a human figure into the chamber of Carrowkeel Cairn G (Video: Aaron Watson)

One of the advantages offered by the roof-box is that projected images, along with the light from the midsummer sun, would not have been interrupted by people moving through the passage.

A further account of these observations will be posted in due course.