Knowth | astronomical features | counting the moon | Lunar calandars

Reconstructed woodhenge near the east entrance at Knowth. This structure is thought to date to about a thousand years after the big mound.

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Knowth - astronomical features

The passages of the central mound appear to be aligned to the equinox sunrise and sunset, one opening towards the east, the other to the west. However, apart from the work of Martin Brennan in the 70's and early 80's, little concern has been shown for any possible alignments at Knowth. This is quite surprising, given the obvious interest in astronomy shown at Newgrange a kilometer away.

Both of the passages have standing stones outside them, which cast shadows on their respective entrance stones around the equinoxes. The entrance stones have vertical marks engraved on them as with Kerbstones 1 and 52 at Newgrange. The entrances to both large passages were extensively disturbed in the Iron Age when the mound was fortified, so we don't know if there were any roofbox structutres, or other astronomical features. The shameful blocking of the entrance of the east passage with a slab of concrete makes it impossible to visually check any alignment with the equinox.

Though it is difficult to get an exact measurement, it appears that the passages are not aligned due east and west. The east pasage is oriented to about 83°, perhaps a week after the spring and before the autumn equinox. The west passage is also a week to 10 days off the equinox sunsets. The west passage has a 'kink' about three-quarters of the way in, which may be the remains of an earlier mound which was altered by the construction of the great mound.

Right: kerbstone with engraving of possible astronomical symbolism. Most of the art at Knowth seems concerned with lunar symbolism. Drawing by Martin Brennan.

Knowth has a wealth of lunar symbolism, and more recent research - mainly on internet discussion lists - tends towards lunar alignments and cycles at Knowth. The 17 or 18 satellite mounds suggest the 18.6 year lunar cycle, which seems to have been of great interest to the ancient Irish and was studied at Cairn G in Carrowkeel. The satellites more than likely aligned to different phases of the moon, and used over a lengthly period of time before the main mound was built. Site 2 and Site 4 look as if they may be aligned to summer moon rises and extreme summer rises, and Site 2 has a specific solar/lunar engraving in the right-hand recess. The art at Knowth seems, to me, to speak for itself when it comes to lunar motifs.

My own guess - which follows Brennan - would be that at certain times, at least twice in the 18.6 year lunar cycle, the chambers of Knowth's main mound are lit by both the sun and moon at the same time. This would indeed be a feat which would match the size, scale, cosmic grandur and design of Knowth. This grand double alignment specifically fits with the design carved within the great basin stone from the east chamber.

Kerbstone with engraving overlaid with one of Brennan's drawings.

A long, thin stone, with a groove along one side and ribs along the other, terminating in a headpiece with three engraved ovals. Found near the entrance to the west passage. Generally called a phallic object, it may have been used as a sightpiece for making astronomical observations, a mesuring device or as a holder for a stringed pendelum. From Knowth by George Eogan.

This kerbstone is thought by Martin Brennan to represent the moon in it's various phases. It is located not far to the north of the east entrance.