Prehistoric Tombs Were Early Humans' Observatories

Some of the mysterious prehistoric mounds known as "passage graves" were not merely tombs. They provided a way for our ancestors to observe the movements of stars, according to Nottingham Trent University scientists - making them 6,000-year-old observatories.

Passage graves are found throughout the Atlantic seaboard of Europe, in countries such as the UK, Ireland, Germany, the Netherlands, Portugal and Spain. They are chambers built inside the earth by people of the Neolithic Era - the New Stone Age. Many, though not all, contain evidence of prehistoric human burial, and they are often marked by a visible megalithic structure such as a dolmen.

The idea that these Neolithic tombs could have an astronomical purpose is hardly far-fetched. The claim has been made for various sites, including the Boyne Valley monuments of Ireland. These appear to have been in alignment with the equinoxes of the period in which they were built. Newgrange, the best known of them, is apparently arranged in such a way that when the sun rises on the date of the winter solstice, sunlight floods through the inner chamber - as detailed by World Heritage Ireland.

The researchers from NTU and the University of Wales Trinity Saint David (UWTSD) have a special interest in the 6,000-year-old Seven-Stone Antas of central Portugal.

"The range of orientations of these monuments corresponds almost exactly to the range of possible sunrise positions during the year... providing remarkably strong evidence of an association between these tombs and the sun," notes the British archaeoastronomer Clive Ruggles.

However, the research team is interested in their association with the stars - in particular, Aldebaran, the brightest of the stars in the constellation Taurus, says the NTU press announcement. The researchers speculate that the first sighting of Aldebaran after a long absence served as a seasonal marker that could signal, as one possibility, the start of herds' migration to their summer grazing grounds.

Knowledge of this timing would have appeared to reflect arcane foresight on the part of the star watchers. One can imagine a wise elder performing a nightly "communion" with the ancestors until the time of the appearance of Aldebaran.

The researchers suggest this was made possibile by the construction of the passage grave, where a long, narrow corridor provides the optimal viewing conditions for observing the night sky. The observer would have waited in the tomb after dark, when no natural light could enter apart from any starlight shining through the small opening provided. These conditions would have enhanced the appearance of the night sky brightness and color for the watcher within.

"The key thing is that a passage grave with its long corridor acts like a telescope that does not have a lens - it is a long tube from which you are looking at the sky," explains UWTSD researcher Fabio Silva in The Guardian. He says that the team will attempt to replicate what the passage grave builders are speculated to have done. "We are going to simulate this star rising at twilight conditions and allow people to tell us when they can see it."