The meaning of light … the passage into Maeshowe chambered tomb, on Mainland, Orkney Islands. Photograph: Murdo Macleod

It is time to pray for the return of the sun. In this deep midwinter, we can start to imagine what the winter solstice meant to the ancient inhabitants of Britain who built Stonehenge and Maeshowe, and who aligned these mysterious buildings to receive the remote rays of the sun on the darkest day of the year.

This is the holiest time of the year – if you happen to share the beliefs of these ancient pagans, which, in fact, are obscure because they left no writings or even much in the way of figurative art. But the winter solstice must have been deeply important to them because on this day, and this day only, sunlight creates startling effects at Britain’s late neolithic and early bronze age monuments. Most astonishingly of all, it enters the long narrow entrance passage of the burial mound of Maeshowe on Orkney’s Mainland island and glows on the back wall of the inner chamber. The building becomes a giant camera, catching sunlight in a moment of mystery and wonder.

The architecture of Maeshowe is one of the marvels of these islands. Inside the earthen mound is a profoundly impressive chamber made of massive blocks of stone arranged in powerful lintels neatly layered, perforated by accurately rectangular openings. There is a precision to the stone construction and its plan, with symmetrical side chambers. When later Viking warriors broke into the chamber they wrote runic inscriptions on its stones, adding to the strange atmosphere. But it is at the winter solstice that Maeshowe consummates its mystery with the astronomical spectacle of the sun piercing its dark sanctum of death.

Light in darkness, life in death, the moment when the sun begins its return journey towards midsummer. Truly the pagan midwinter is a moving celebration. But, as we rush around buying presents, do we remember the true meaning of the winter sun festival?