West entrance gnomon shadow at Knowth

An interesting feature of the passage entrances at Knowth is that they both had standing stones positioned just outside the entrance kerbstones. When the site was excavated, both stones were found in a fallen position, but the western standing stone was later re-erected.

On the evening of maximum penetration of the setting sun into Knowth West, March 3rd, the standing stone casts a shadow on the entrance kerbstone. It does this for a number of evenings at certain times of the year, but it is on the day of maximum penetration that the shadow appears to line up against the central vertical line of the entrance kerbstone just as the sun sets.

The photographic sequence below shows the actual event in progression. These photographs were taken on March 5th, two days after maximum penetration, but they aptly demonstrate how the event happens. Regrettably, the shadow becomes very faded and obscure by the time it reaches the vertical line, but naked eye observations confirmed the shadow was still visible at this critical point.

An additional difficulty is the sunlight, which becomes very diffused. This may be partly due to a large tree which sits in a direct line with the setting sun - it seemed that the foliage of the tree was scattering the sun's light, causing the definition of the shadow to fade.

The tree which sits in line with the western passage at Knowth. The foliage of this tree may be responsible for scattering the sun's light at the crucial moment when the standing stone shadow lines up with the vertical line on the entrance stone at Knowth west. One of the satellite mounds, site 6, was thankfully reconstructed so that it does not hinder the sunlight from entering the western passage.

Other pages of interest: Exclusive pictures showing sunlight inside Knowth west.
Photographs of the carvings on the stones inside Knowth's western passage.
See aerial photographs of Knowth and its satellite mounds.