Ancient standing stone monuments in Scotland were astronomical devices, scientists found.

About 500 years before Stonehenge's famous monuments were constructed in England, a group of smaller stone circles was built on the Isle of Lewis and the Isle of Orkney in Scotland. Researchers from the University of Adelaide in Australia discovered that the 5,000-year-old "stone circles" had been constructed to align with the sun and moon's movements.

"Nobody before this has ever statistically determined that a single stone circle was constructed with astronomical phenomena in mind - it was all supposition," Gail Higginbottom, University of Adelaide Visiting Research Fellow and project leader, said in a statement.

"This research is finally proof that the ancient Britons connected the Earth to the sky with their earliest standing stones, and that this practice continued in the same way for 2,000 years."

Using 2D and 3D technology, the researchers constructed quantitative tests of the alignment patterns of the standing stones. The team also studied the simpler stone monuments built 2,000 years after the stone circles were created.

After examining the sites, the researchers found that about half of the sites were placed in landscapes with higher and closer northern horizon and a lower horizon to the south. This makes the summer solstice Sun rise out of the highest peak in the north - marking the longest day of the year.

The other half was completely reversed - the southern horizon was higher and closer, which means the winter solstice Sun rises at the highest peak to the south - marking the shortest day of the year, the researchers said.

According to Higginbottom, these events occur only once every 18.6 years, and recognizing the significance of these movements would have taken considerable astronomical knowledge.

"It would take at least three generations of constant observations, even if you were already watching for it, to notice that when the Moon is as far south as it gets it rises in the same place," Higginbottom said in a report by IFL Science.

The study was published in the Journal of Archaeological Science: Reports.