* Astronomy

Bryn Celli Ddu is a prehistoric site on the Welsh island of Anglesey located near Llanddaniel Fab. Its name is difficult to translate directly but means either 'the mound in the dark grove' or possibly 'the mound in the grove of the deity'. It was plundered in 1699 and archaeologically excavated between 1928 and 1929.
During the Neolithic period a stone circle and henge stood at the site. An area of burnt material containing a small human bone from the ear, covered with a flat stone, was recovered.
The stones were removed in the early Bronze Age when an archetypal passage grave was built over the top of the centre of the henge. A carved stone with a twisting, serpentine design stood in the burial chamber. It has since been moved to the National Museum of Wales and replaced with a replica standing outside. An earth barrow covering the grave is a twentieth century restoration; the original was probably much bigger.
Norman Lockyer, who in 1906 published the first systematic study of megalithic astronomy, had argued that Bryn Celli Ddu marked the summer solstice. This was ridiculed at the time, but recent research by Steve Burrow, curator of Neolithic archaeology at Amgueddfa Cymru (National Museum of Wales) has proven his theory to be true. This alignment links Bryn Celli Ddu to a handful of other sites, including Maes Howe and Newgrange, both of which point to the midwinter solstice. It has also been suggested that a feature similar to the 'lightbox' at Newgrange may be matched at Bryn Celli Ddu (Pitts, 2006).
A row of five postholes previously thought to have been contemporary with the tomb (c. 3000 BC) have recently been proven to be much earlier. Early results from a radiocarbon programme date pine charcoal from two of the pits to the Mesolithic (Pitts, 2006).