shadow appears to descend the west balustrade of the northern stairway. The visual effect is of a serpent descending the stairway, with its head at the base in light. Additionally the western face points to sunset around 25 May, traditionally the date of transition from the dry to the rainy season. The intended alignment was, however, likely incorporated in the northern (main) facade of the temple, as it corresponds to sunsets on May 20 and July 24, recorded also by the central axis of Castillo at Tulum. The two dates are separated by 65 and 300 days, and it has been shown that the solar orientations in Mesoamerica regularly correspond to dates separated by calendrically significant intervals (multiples of 13 and 20 days). In their discussion of the credibility of archaeoastronomical sites, Cotte and Ruggles used the "equinox hierophany" at Chichén Itzá as an example of an Unproven site, the third of their four levels of credibility. Stonehenge Many astronomical alignments have been claimed for Stonehenge, a complex of megaliths and earthworks in the Salisbury Plain of England. The most famous of these is the midsummer alignment, where the Sun rises over the Heel Stone. However, this interpretation has been challenged by some archaeologists who argue that the midwinter alignment, where the viewer is outside Stonehenge and sees the Sun setting in the henge, is the more significant alignment, and the midsummer alignment may be a coincidence due to local topography. In their discussion of the credibility of archaeoastronomical sites, Cotte and Ruggles gave Stonehenge as an example of a Generally accepted site, the highest of their four levels of credibility. As well as solar alignments, there are proposed lunar alignments. The four station stones mark out a rectangle. The short sides point towards the midsummer sunrise and midwinter sunset. The long sides if viewed towards the south-east, face the most southerly rising of the Moon. Aveni notes that these lunar alignments have never gained the acceptance that the solar alignments have received. The Heel Stone azimuth is one-seventh of circumference, matching the latitude of Avebury, while summer solstice sunrise azimuth is no longer equal to the construction era direction. Maeshowe This is an architecturally outstanding Neolithic chambered tomb on the mainland of Orkney, Scotland—probably dating to the early 3rd millennium BC, and where the setting Sun at midwinter shines down the entrance passage into the central chamber (see Newgrange).