The large entrance kerbstone K1, above, marks the entrance to the chamber of Dowth South. Although this entrance stone has fallen forwards, an engraved spiral and some cupmarks can be seen carved into it. There is no public access to this chamber in general, and permission from the Office of Public Works to visit. However it is usually opened for the winter solstice sunset, when visitors who have gathered for the sunrise at Newgrange can come to Dowth to witness the sunset on the same day.
The passage is four meters long and constructed with three orthostats on each side. The passage opens into a round chamber, about five meters in diameter, with a sill stone dividing the passage from the chamber. There are twelve orthostats forming the roughly round chamber and an empty space where there may have been a thirteenth.
The structure was originaly roofed with a massive corbelled beehive vault which had collapsed in antiquity, or was damaged during Firth's excavation in 1847. George Coffey states that the chamber had no roof in the 1880's. A concrete roof was added around that time, but does a poor job of keeping the chamber, which is always muddy, dry.
This circular chamber has an unusual plan when compared to other Irish megalithic monuments: there is only one recess, formed from three massive slabs on the south or right-hand side of the space. Another sill stone divides the recess from the chamber. The construction of this recess is on a monumental scale, with some of the stones almost three meters long. The roof is constructed using massive corbelling, and seems to have been repaired during the 1880's renovations, when spall stones were inserted under the slabs.
There are several small engravings in the right recess which are similar to and probably derived from the sun wheels and rayed circles of Loughcrew
Winter Solstice Sunset
The fact that the south chamber of Dowth is oriented towards the winter solstice sunset was first noted by American researcher Martin Brennan in his book, The Stars and the Stones, published in 1983. A broad beam of sunlight enters the passage at 4.15 pm, sweeps across the floor and illuminates the decorated stone at the back of the chamber. The stone to the left of the sunbeam, which is carved with an array of diamonds, lozanges and zig-zags, the most complex panel of art at Dowth, remains in darkness. The reflected light seeps the recess to the right.
American researcher and archaeoastronomer Martin Brennan concluded that the mounds in the Boyne Valley were linked in an annual cycle of ritual astronomical observations. He found that the suns rays entered several of the mounds on the winter solstice, beginning with Newgrange and ending with this chamber in Dowth South.
The entrance of Dowth faces out towards Newgrange and the horizon beyond. Dowth acts as a synchronized counterpart of Newgrange. On the day of winter solstice the sun projects its rays into Newgrange at dawn and into Dowth at sunset. The passage and chamber at Dowth are about half the size of their Newgrange counter parts, but the projected light beam is much larger, and it remains in the chamber for a longer period of time, creating an even more dramatic spectacle. Parallels can be drawn between Dowth, and Loughcrew and Knowth, where passages are aligned to both the sunrise and sunset of a particular astronomical event. At Dowth a large circle hollowed into the entrance stone marks the position of the setting sun. The entrance stones at Dowth and Newgrange have similarities, but the Newgrange one is more formalized and clearly a later development in both technique and concept.
A second, larger passage at Dowth is also aligned to sunset. The original entrance to this passage was sealed during reconstruction. It seems to mark the cross-quarter days on 8 November and 4 February. The three gigantic mounds in the Boyne Valley, made up of hun dreds of thousands of tons of material, in fact form a unified system that follows the circuit of the sun from the autumnal equinox to the spring equinox. It seems that after spring equinox interest shifts to lunar observation.
The Stars and the Stones, Martin Brennan, 1983.