Solstice at Newgrange

The Winter Solstice at Newgrange
Once a year, at the winter solstice, the rising sun shines directly along the long passage into a chamber for about 17 minutes and illuminates the chamber floor. It is thought that the alignment is too precise to have occurred by chance. The sun enters the passage through a specially contrived opening, known as a roofbox, directly above the main entrance. The alignment is such that although the roofbox is above the passage entrance, the light hits the floor of the inner chamber.
Today the first light enters about four minutes after sunrise, but calculations based on the precession of the Earth show that 5000 years ago first light would have entered exactly at sunrise.