By Dr David Whitehouse
BBC News Online science editor
Many Bronze Age monuments in Europe and Africa were erected with the Sun and other stars in mind, says Dr Michael Hoskin, a UK historian of astronomy.
So many tombs built to get a clear view of the rising Sun
In one survey of 2,000 tombs he has shown how many were built to face the rising Sun - a symbol of the afterlife.
A second study of stone structures in Menorca reveals they were set up to view the constellation of Centaurus.
The Cambridge University researcher has discussed his work at the 2004 National Astronomy Meeting in Milton Keyes.
God of healing
The Menorcan study centres on "taulas" - from the Catalan word for table - which are rectangular stones set in bedrock with a horizontal slab placed across the top of them - to form what looks like a capital "T".
These structures, which are built on elevated ground, are surrounded with walls that have openings which, according to Dr Hoskin, almost invariably point towards the south.
"This cannot have happened by chance," he says, "so why was it necessary that the worshippers in the sanctuary should have a perfect view of the southern horizon?"
Today, there is nothing in the sky, low to the south, which is of particular interest. But in 1,000 BC when the taulas were built, the Menorcans could have seen the constellation of the Southern Cross and the bright stars of Centaurus rising and setting in that direction.
Sign of hope
In Greek mythology, the Centaur, Chiron, taught the god of medicine.
"Of course we do not know if the taula builders had a similar mythology," said Dr Hoskin, "but it is very possible, and the link with healing would explain the extraordinary discovery in one taula sanctuary of a bronze statue from Egypt with an inscription saying, 'I am the god of medicine'."
In a separate investigation, Dr Hoskin described how he spent more than a decade visiting about 2,000 Neolithic tombs in Europe and North Africa.
He found that the great majority of the entrances to these constructions faced the rising Sun.
"It is remarkable that communities over so vast an area all chose to orient their tombs towards the rising or climbing Sun," he said.
"Presumably they did it because the Sun was a sign of hope and the symbol of the afterlife."