Megalithic or ancient stone tombs housed the dead after they breathed their last, but a new study suggests that these prehistoric structures may have been of use to the living, too.

The long, constricted entry to these megalithic tombs may have been an "advanced" method of viewing the stars for early human cultures.

Indeed, the 6,000-year-old megalithic graves located in Portugal may have been the world's first astronomical telescope, albeit without the lens, researchers in the United Kingdom said.

It worked because the passageways created a tunnel effect that made it easier to observe the stars, says Fabio Silva, an astronomer from the University of Wales Trinity Saint David.

He says it is basically just a long tube for looking at the sky, and that its features affected how one could see the sky. For instance, these characteristics include directing your focus to one specific portion of the sky, while also blocking out distractions of other planets and stars.

It is also possible that because the megalithic structure's environment was lightless, it helped the eyes adjust to the dark, allowing the person to distinguish faint details such as distant stars.

Daniel Brown of Nottingham Trent University, another member of the research team, says the effect of the megalithic structure is ensuring that everything is dark aside from the small area in the sky.

Brown, Silva and their colleagues believe that the entrance passageways, especially the Seven-Stone Antas located in central Portugal, may not have been positioned by accident.

Silva said the orientations of the megalithic tombs themselves may be in alignment with the brightest star in the Taurus constellation, which is known as Aldebaran. In order to accurately time the first appearance of Aldebaran in the season, it is important to be able to detect stars even during twilight.

Furthermore, researchers suggest that the megalithic tombs may have also been used as calendar aids that help them mark the change in season. This helps them become aware of the right time to move to grazing grounds in spring.

The ancient stone tombs may have also been used as ritualistic devices, which conferred knowledge to those who are allowed inside the graves, or as a rite of passage that involved youngsters.

Silva says a young boy, who was probably scared to death, may have been forced to spend the night in the ancient passage. In the morning, the young boy would see the star rise before the rest of his tribe. This was probably considered as secret knowledge or foresight, and ancient humans probably believed that the knowledge was gained after a night spent "in contact" with dead ancestors who were buried in the grave.

In the meantime, researchers plan to expand their hypothesis by replicating the entrance passageway viewing conditions.

Silva says they will simulate the star rising at twilight and ask people to tell them what they see. They will then compare it to a control group in a room that replicates the condition of being outside the tombs.

Details of the study were presented at the National Astronomy Meeting in Nottingham.

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