Two studies of ancient monuments in southwest Europe reveal the influence the Sun and stars had on their builders according to Dr Michael Hoskin, a historian of astronomy at Cambridge University.

In the Archeoastronomy session of the RAS National Astronomy Meeting at the Open University, he will argue that the orientation of about 30 Bronze Age sanctuaries on the island of Menorca with a clear view towards the southern constellation Centaurus, favours his interpretation of them as places of healing, such as Lourdes in France is today. He will also tell the meeting how his own measurements of the orientation of around 2000 Neolithic tombs in western Europe and North Africa reveal that the overwhelming majority were built to face the rising Sun.

Known as "taulas" from the Catalan word for table, the Menorcan Bronze Age sanctuaries have at their centre a rectangular stone set vertically into the bedrock, and on top of this is a second, horizontal slab, so that the two stones together have the form of a capital T. Around this central feature is a precinct wall and an entrance, and the central feature faces out through the entrance, so that the monument has a well-defined orientation.

All but one of the thirty or so taula sanctuaries face roughly towards the south and they are all located on elevated ground with a perfect view towards the south - some look out to sea, while others look down across a plain. "This cannot have happened by chance, so why was it necessary that the worshippers in the sanctuary should have a perfect view to the southern horizon?" asks Dr Hoskin.

Today there is nothing in the sky, low to the south, that is of any interest. But in 1000 BC when the taulas were built, the Menorcans could have seen the Southern Cross and the bright stars of Centaurus rising and setting towards the south. 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," says 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 in hieroglyphics saying "I am the god of medicine." The sanctuaries could well have been places of healing, rather as Lourdes is at the present day."

In an account of a separate investigation, Michael Hoskin will describe how he spent a dozen years visiting some 2000 Neolithic communal tombs in France, Spain, Portugal, the Mediterranean islands and North Africa, recording the directions their entrances face. He discovered that they are far from random. Customs varied to some extent from one area to another but the great majority face a direction in which the Sun can be seen to be rising or climbing in the sky. Only in part of southern France were tombs built facing the setting Sun instead.

"It is remarkable that communities over so vast an area should all choose to orient their tombs towards the rising or climbing Sun," says Dr Hoskin. "Presumably they did it because the Sun was a sign of hope and the symbol of an afterlife."