Astronomy and megaliths

Imagine - you are young and have only seen the passage of a few seasons, but now you need to grow the food that sustains your family. You see the hand of Death steal across the countryside as Summer turns to Autumn. The leaves fall from the trees, thedays grow short and the nights grow long and cold. You have no light, save that of flickering fires which need forays into the cold for fuel. And you see the giver of warmth, of Light, and of Life, grow watery and weak.

This matters to you, in a way that it is almost impossible for anyone reading this screen to know. More than five thousand years must pass before Galileo raises the idea that the Earth passes round the Sun and Kepler establishes the slightly elliptic orbit - in short before there is an intellectual framework which tells us why each Winter holds the promise of a Spring.

With the advent of writing, this cycle of the seasons could be documented as well as observed, and its regularity handed down across the generations. In that regularity came security - but writing lies more than a thousand years in the future.

This knowledge of the seasons in important - important to know when to plant and when to reap the harvest in practical terms. And spiritually it matters too - to feel that at the time when the spirit swings low deep in the darkness of midwinter, there is a symbol which stands to mark the time when the darkness ceases to overcome the light. Often it was the local megalithic site that marked this turning point.

We see this at Newgrange, when the long passageway is so aligned that only the midwinter sunrise illuminates the central chamber. And though Stonehenge is associated in the popular imagination with the midsummer sun rising over the Heel Stone, it is more likely that it is the precious light of the midwinter sun shining through the stones at the winter solstice which was celebrated by its makers.

The sun, of course, is not the only celestial body - the Moon has symbolic and religious significance, and many of the recumbent stone circles of Aberdeenshire, Scotland, are aligned with lunar events. The rising of the Moon viewed from a fixed point on Earth is more complex than that of the sun, with a periodicity of 18.6 years so much more careful observation, possibly spanning more than one person's lifetime would be needed to determine the alignments.

Alignments with stars are more difficult to establish clearly - partly because the positions of some stars in the sky is not the same now as it was in prehistoric times and partly because the large number of stars give many possible sight-lines - not all of which were necessarily intended by the builders.