Twenty people squeezed themselves into a tight chamber in Ireland on Sunday, the shortest day of the year in the Northern Hemisphere, to marvel at a prehistoric "calendar clock" in operation.

About 19,200 people applied this year for a coveted place inside the Newgrange tomb in County Meath to watch the phenomenon of the sun's rays on the midwinter solstice dramatically beaming deep into the burial mound. Only 20 people can fit into the 19-metre long chamber of the immense tomb north of Dublin.

Newgrange, believed to be the world's oldest continuously roofed building, is orientated towards the rising sun.

It was built 1,000 years before Britain's Stonehenge and 500 years before Egypt's pyramids.

Modern scientists are astonished that the Stone Age builders over 5,000 years ago had the architectural skills and understanding of the movement of the sun to construct it.

Only at the midwinter solstice - the shortest day of the year on December 21 - does the rising sun shine all the way down the passage into the centre of the tomb. The phenomenon only lasts 17 minutes

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