Bryn Celli Ddu (pronounced approximately ‘Brin Kethlee Thee’) is a restored passage tomb on the island of Anglesey on the north Wales coast. Built on top of a destroyed henge and stone circle, it is a late example of the type of chambered tombs built during the Neolithic, between 5-6,000 years ago. The restored mound is a fraction of its original size, but the passage and chamber are much the same as they would have been originally.
In 1906, Sir Norman Lockyer published one of the first systematic studies of megalithic astronomy. Based on observations made at Easter, he predicted a summer solstice alignment at Bryn Celli Ddu. This idea was not take seriously at the time and the notion fell into obscurity until archaeologist Steve Burrow came across Lockyer’s book. In 2005, he was able to make observations that proved Lockyer correct. The discovery was widely publicised at the time and a video of the sunrise can be viewed in the museum in Cardiff. Click here to read the BBC report.
During an otherwise very cloudy and damp holiday on Anglesey this summer, I was fortunate enough to have one very fine, clear morning. A very early start at 4.20am was well rewarded with a spectacular light show inside the chamber, click to play the slideshow below:
Click here to view a larger version of the slideshow on the website, should also work on the iPhone/iPad and other mobile devices.
Although the morning I was in the chamber was a couple of weeks after the solstice, the rising position of the sun moves so slowly during the solstice period that the phenomenon changes only slightly over the weeks before and after the ‘standstill’. See the diagrams below to see how the sun’s angle at sunrise changes over a couple of weeks. The length of the passage is also quite short compared to Newgrange or Knowth, which also extends the window of of time during which the light beam can be observed.
The yellow lines depict the angle of the sun at sunrise on each of the dates, compare where the line passes through the buildings in the farmyard. Screenshots are from the excellent Lighttrac app for the iPad
Shadows and Stone Blog 
Cannot thank you enough for the brilliant slide show pictures. I am writing a book that features Bryn Celli Ddu at sunrise and was desperate for some clear pictures of the progression of the dagger of light at Summer Solstice. Your pictures are perfect. Thank you!