Much of our culture has been shaped by what ancient humans thought about while looking at the night sky. Myths and legends, gods and demons, all are influenced by our ancestors' observations of the movements of the planets and stars. And now, researchers have uncovered one of the earliest tools that they used to make those observations: a telescope from six thousand years ago.

While a modern telescope works by magnifying images with mirrors or lenses, this ancient structure is a long, narrow corridor designed to filter out unwanted light. The corridor helps when viewing stars during the hours of dawn and twilight, when the light from the sun makes it hard to view stars near the horizon.

The structure is part of a what's called a "passage grave," a prehistoric tomb with a long entrance corridor. Passage graves are found throughout Europe, and scientists are just starting to examine the astronomical uses of their entrances. The researchers are focusing on a particular passage grave, the Seven-Stone Antas in central Portugal, which is about 6,000 years old.

a) Dolmen da Orca, a typical passage grave in western Iberia; b) view of the corridor from the inside; c) Orca de Santo Tisco, a smaller passage grave. Credit: Dr Fabio Silva

The researchers believe that the Seven-Stone Antas corridor was used to view the star Aldebaran, the red giant in the constellation Taurus. Aldebaran first becomes visible in the Northern Hemisphere in the early morning of late April, just before sunrise, and viewing it through the passage could make it visible days earlier. Aldebaran likely was a seasonal marker, and its appearance would signal migration patterns or weather changes.

The researchers are now studying other passage graves, in the hope of learning more about prehistoric people.

Source: Royal Astronomical Society

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