It’s a marvel of early astronomy that never fails to amaze because Newgrange actually predates the great pyramid of Giza in Egypt by at least 500 years. Built somewhere between 3100 and 2900 B.C., the famous passage tomb at Newgrange is estimated to be approximately 5,000 years old, even predating Stonehenge in Britain by 1,000 years.
The sunlight enters the passage through a specially opening, known as a roofbox, directly above the main entrance.it then hits the back of the corridor and slowly makes it's way to the entrance. Although solar alignments are not all that uncommon among prehistoric passage graves, Newgrange is one of few to contain the additional roofbox above the passage entrance, a sophisticated construction allowing the light to hit the floor of the inner chamber.

On the 21st of December 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. That makes the solar alignment at Newgrange very precise compared to similar phenomena at other passage graves in England and Scotland.