The Moon in Archaeoastronomy

 In a complicated way, the Moon's long-term variation of 18.61 years in rising points overlaps with the cycle of phases. As a result, a standstill can occur even at a new Moon and thus go unnoticed. However, during the lunistice year, the Moon will have monthly maximal and minimal declinations that are all very close to the lunistices, despite the fact that they only correspond to them once. An interesting phenomenon occurs now as a result of the characteristics of the Moon's motion. In fact, the full moon closest to the summer solstice is always at the minimum declination, and the full moon closest to the winter solstice is always at the maximum declination.

In the lunistice year, both spectacles are well worth seeing. The full moon near the winter solstice – the year's longest night – rises very high in the sky (higher than the Sun at the summer solstice, in particular) and stays there the longest; at high latitudes, it can even become circumpolar. The full Moon near the summer solstice – the year's shortest night – reaches its lowest elevation ever.

When considering the possibility that ancient astronomers and architects were interested in the Moon's extreme positions, it's better to think of a general fascination with these (fully visible and spectacular) phenomena rather than extremely precise lunar azimuth measurements at standstills.

As a result, previous claims of extremely precise lunar alignments made about megalithic monuments in northern Europe in the 1960s and 1970s are now considered implausible. In the archaeoastronomical literature, however, there are convincing cases of alignments to the full Moon at standstills.

I'll use the case of Chimney Rock is an example. It's a "pueblo," or village, built by the Anasazi, the forefathers of today's American Indian tribes living along the Rio Grande. Around 1000 AD, Anasazi culture flourished in the area that today is the border between Utah, Colorado, Arizona, and New Mexico.

The Chimney Rock Pueblo is built on a desolate hill ridge with no water sources; its existence for functional purposes is difficult to explain. The landscape is unique, however, because two spectacular rocks or "chimneys" dominate the horizon to the north-east.

Figure 1  Chimney Rock. The full Moon at the standstill rises between the chimneys (Courtesy Kim Malville).

From the Pueblo's east court, one can get a great view of the chimneys and even sit on an ancient bench that appears to have been built specifically for this purpose.

As a result, it's possible that the Pueblo was built, at least in part, with the intention of using the double chimneys as foresight for the observation of astronomical phenomena. The moon, which is nearing maximum declination, rises between the chimneys in particular.

The required minimum decline is around half a degree lower than the standstill decline. The moon's rise is, therefore, visible every 18.6 years for about three years.

With a method of dendrochronology, it is possible to link lunar standstills with a chronology of the Pueblo, which allows structures to date from wood by analysis of tree rings. Indeed, in 1076 AD, a year of great lunar settlement, the initial construction of Chimney Rock, and in 1093 immediately before the subsequent lunar settlement was expanded.

The performance was, and is, quite impressive, even greater for the Anasazi if the twin rock tower was, as was suggested, perceived as the sanctuary of a few Twin Gods, associated with War, Sun, and Moon children (Malville, 2008).