Passage Graves from 4000 BCE May Have Been Used as Telescopes

Astronomers from the UK are studying the use of passage graves as astronomical tools dating back to approximately 4,000 BCE, millennia before Galileo looked towards the night sky. Researchers from Nottingham Trent University and the University of Wales Trinity Saint David contend that the long narrow passages, entrances to megalithic tombs dating from the Neolithic period, enhanced the visibility of the night sky, much like a telescope, for early human societies.

The team is currently examining the 6,000-year-old passage graves located in Carregal do Sal, Portugal, where they discovered that 13 tombs were constructed with their entrances aligned with the brightest star found in the Taurus constellation, Aldebaran. They’ve found that when standing in the center of a completely dark tomb, even the faintest stars are visible when looking out through the passage way.

Passage graves, stone tombs with a large chamber accessed by a long, narrow tunnel, have been discovered all along the Atlantic coastline of northwest Europe (more than a thousand have been documented to date) in Britain, Ireland, Scandinavia, northern Germany and the Drenthe area of the Netherlands. They’ve also been found in Iberia, parts of the Mediterranean, and on the coast of north Africa.

As Dr. Fabio Silva, the team’s lead researcher, explained to the Daily Mail, in order to accurately detect and time the very first appearance of this star, it has to be viewed at twilight. At the time the graves were constructed, between 4,300 and 3,700 BCE, Aldebaran would have risen between April 18th and 27th, in the exact spot in the sky that’s visible from inside every entrance passage at Carregal do Sal.

The first sighting of Aldebaran may have been used by early humans to mark the seasons. Upon the star’s arrival, Neolithic communities would have likely moved their cattle to higher pastures located nearby in Serra da Estrela.

Additionally, given that the tombs were widely considered sacred places, this ability to detect stars too faint for anyone outside of the tomb to see may have been considered a sort of secret knowledge, obtainable only in the company of their deceased ancestors.

How does it work? There are several factors at play, according to what Dr. Silva told the Daily Mail. The long entrance behaves like a telescope without a lens, simply a long tube, the characteristics of which affect how and what you see. For instance, your attention is directed to a particular area while the distraction of other stars is removed, and the total darkness of the structure would be helpful for adjusting your eyes to the darkness of the sky – which in turn makes it easier to detect faint details like distant stars.

Previous studies have shown that the majority of passage tombs located in Portugal are positioned to align with two or three different stars, Aldebaran being the primary attraction. Although there are over a thousand known passage graves throughout Europe, it’s estimated that only around 10% of them are oriented towards a particular star, including the well-known passage graves at Bryn-celli-Ddu on Anglesey, and Newgrange in Ireland; which appear to have been orientated towards either the sunset or sunrise on the winter or summer solstice.

The research was presented at the 2016 Royal Astronomical Society’s national meeting during a special session about how historical societies and cultures studied the sky.

Image courtesy of ESO/Luis Calçada/Herbert Zodet

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