Newgrange is a 5,000 year old prehistoric tomb monument in County Meath, Ireland, north of the River Boyne. Built in 3,200 BC, the site comprises of a large circular mound with a passageway and interior chambers made up of stones.
The site is famous for Winter Solstice Illumination that occurs once a year. A few days around the winter solstice, the rising sun flings its light along the long passageway. This light illuminates the heart of the tomb, revealing the carvings inside. The illumination last for around 17 minutes. The sunlight enters the passage via a roofbox, an opening situated above the doorway. It is this roofbox that has led people to believe that the tomb was built with an astronomical viewpoint.
This even was first observed by M. J. O’Kelly on 21st December, 1967. Today the first light enters about four minutes after sunrise, but calculations based on the precession of the Earth show that 5,000 years ago first light would have entered exactly at sunrise.
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