The West Trilithon
The West Trilithon participates in more alignments than any other structure in STARHENGE. Like the East and South Trilithons, it is about 16 feet tall. The lintel is perforated with a 3-inch diameter aperture that is slotted north-south on the lower surface, permitting the sun and moon to cast images on the vertical face of the northern upright at transit (local noon for the sun). The image of the noon sun will track up and down the face of the upright with the seasons, falling near the base at the summer solstice and near the top at the winter solstice; the full moon images will track in an inverse pattern with respect to the seasons, higest in summer and lowest in winter.
Standing between the uprights, or within the circle gazing outward through this opening, the winter solstice, summer solstice, and spring and fall equinox sunsets are marked by heel stones located in the double spiral geoglyph.
Finally, Antares, Arcturus, Deneb and the Pleiades can be observed to set through the Trilithon opening as indicated in the diagram below.