Newgrange is best known for the
illumination of its passage and chamber by the winter solstice sun. Above
the entrance to the passage at Newgrange there is a opening called a
roof-box. It’s purpose is to allow
sunlight to penetrate the chamber on the shortest days of the year, around
December 21st, the Winter Solstice. At dawn, from December 19th to 23rd, a
narrow beam of light penetrates the roof-box and reaches the floor of the
chamber, gradually extending to the rear of the chamber. As the sun rises higher, the beam widens so
that the whole chamber is dramatically illuminated.