Field Visit

Date 2013

Event ID 994370

Category Recording

Type Field Visit

Permalink http://canmore.org.uk/event/994370

NB 21297 33024 Two stones, numbers 51 and 52, in the NW of the circle at Callanish l are set close to each other. Stone 51 has an overhang on its inner face and has lost its top since Worsaae drew it in 1846, when it appears to have been the tallest stone of the circle.

Stone 52, the adjacent stone to its E, has a ‘shelf’ on its outer face, 2m above the ground. From SW of the circle, the overhang and the ‘shelf’ can be seen to form a rectangular ‘window’ framing a short section of the NE horizon. There is no stone marking the viewing spot. Presumably any such marker has been removed when this area was used for growing crops. At midsummer and midwinter, the rising and setting points of the sun on the horizon vary very little over some two weeks near the solstices. To identify the midsummer’s or midwinter’s day exactly, a precise indication is required - preferably at sunrise - using the first gleam of the sun rather than the tangential full orb of the sun.

When prehistoric people used sunsets for identifying the exact date of solstice, they sometimes used locations from which the midwinter or midsummer sun was first seen to set, then briefly re-appear (re-flash) on one day only. Such accurate indicators would last for only a few centuries.

The paths of the sun and moon have gradually changed since prehistoric times, making it impossible for us to see the same views as prehistoric people saw at midsummer and midwinter 5000 years ago. The midsummer sun’s path is approximately a suns’ diameter further from N, while the midwinter suns’ path is approximately a sun’s diameter further from S. Only at the equinoxes are our views the same as prehistoric peoples. When an indication is unequivocal and precise, it has been used to date the standing stone monument.

A theodolite survey of the ‘midsummer sunrise window’ showed that in prehistoric times, as sunrise positions moved left/northwards and closer to the midsummer rise position, the sun would have first appeared in the ‘window’ formed by stones 51 and 52 seven days before actual midsummer solstice, enabling people to assemble and hold cerenmonies or rituals on the ‘right’ day. Prehistoric people must have selected the two stones and erected them carefully to achieve such accuracy. It is not possible to use the ‘window’ in reverse for midwinter sunset due to the topography around Callanish l.

Be on site by 4.15am BST to observe the sun in the ‘midsummer window’. You will not see the actual sunrise from this location as it is behind stones 50 and 51. As the sun climbs into the sky, its light falls on stone 50 creating a ‘sun dagger’ patch of light.

GR Curtis and MR Curtis, 2013

(Source: DES)