Antas of the Portuguese Alentejo: Structural Orientation to Stars?
				by Robert Oldham, Stones and Stars
			For the people of antiquity, the sky was always overhead. What happened there repeated itself, and these repetitions made it possible to structure time and the world, as they do for us. ... We have always looked to the heavens for orientation and perspective. It satisfies a need. It may be what our brains require to perceive the world at all. Anything might do the job, but the heavens do it well.                                                                                E.C. Krupp, In Search of Ancient Astronomies
		Archaeoastronomy is a multi-disciplinary study examining the mythology and worldviews of prehistoric cultures by the study of their imputed astronomical practices through investigation of the physical remains of their structures. Through an examination of the probable observational practices of such peoples, it is possible to gain an insight into their belief systems and cultural institutions. The astronomical inquiries of the ancient peoples should be seen as the practice of observation and prediction closely tied to their environments, and dependent on their cultural and mythological beliefs and practices for validation.   There are a great many ancient megalithic sites in Portugal, but there is a particular concentration in the area of the Alentejo in South-central Portugal, from Montemor-O-Novo on the West to Elvas on the East, North as far as Portalegre, and South to Beja. The ancient city of Evora is centrally located in this region and is surrounded by hundreds of megalithic monuments. There are single standing stones (menhirs), circles or clusters of menhirs (cromlechs or enclosures), and chamber structures (dolmens). The great majority of megalithic monuments in this region are dolmens, called "antas" by the Portuguese.   These monuments range in size from small chambers about 1.5 meters across and 1.5 meters high inside, to massive chambers such as the Anta Grande do Zambujeiro, 5 to 6 meters across and 4 to 5 meters high inside. The material used in this region is in most cases local granite which has weathered to relatively flat elongated slabs with rounded edges. The chambers are formed by a polygon of 6 to 9 (66% had 7) large flat stones, termed "orthostats", set on end side-by-side or slightly overlapping, and are capped with one or more large slabs laid atop the circle of orthostats. An entrance corridor consisted of two rows of smaller orthostats capped by slabs. The largest chamber orthostat was most often placed first, at the back of the chamber, facing the alignment direction and the corridor entrance, and it is called the "backstone". Many if not all of these structures were originally covered with earth and gravel; many still have the identifiable remains of these "mamoae" and of the corridor.   In November 2001 an orientation survey was undertaken to accurately determine the alignment of the corridor axis of 61 anta sites with respect to astronomical North. The study included a visit by the author to each of the sites. In order to eliminate the unknowns of magnetic variation, the survey measured astronomical alignment based on the precisely-known azimuth of the Sun, using a surveyor's transit. The corridor axis was determined by a combination of the position of the backstone, the apparent chamber entrance opening, and the remains of the corridor. At those sites where the corridor is no longer reliably measurable, the backstone and chamber entrance gap provides an acceptable alternative, though the axis is then less clearly defined. Nearly all alignments fell between 85 and 110 degrees, with prominent clusters at 87, 97, and 104 degrees from North. Because these azimuths do not correspond to significant Sunrise positions such as Solstice, Equinox, or Cross-Quarter, it is postulated that the structures weree aligned to one or more stars or star clusters.   Precession of the Equinoxes causes the Eastern rising point of stars to slowly move North along the horizon; this movement is about 1 degree in 90 years. Using a computer program called StarCalc, the date of Vernal Equinox was determined, and the program was run, for every 500 years between 10,000BC and 1BC. The southernmost prominent cluster of azimuths of the group of 61 antas, which is 104 degrees from North, was checked for rising prominent astronomical objects. The corridors are of sufficient width to permit the passage of a person, and thus allow a view from the backstone of an area of sky about 8 to 10 degrees wide and 8 to 10 degrees high. In tabulating the results of the alignment testing with StarCalc, it was found that the Pleiades star cluster, located in the constellation of Taurus the Bull, rose on the N104E azimuth around 4200BC, and they rose heliacally (just before the Sun) about 2-3 weeks before Vernal Equinox.   The association in about 4200BC with the Pleiades is an intriguing one. Many sources cite the Pleiades as a sacred grouping of stars with figured prominently in the spiritual lives of many ancient cultures. The Greeks probably inherited their tradition about this cluster from their predecessor Neolithic occupants of their region. They held that the Seven Sister were daughters of Atlas and were among the earliest deities to arise; their father was the "grandson" of the first offspring of Gaia, the Earth goddes from whom all else came. Their goddess Athene may have descended from this tradition, since the temple to Athene in Athens, the Parthenon, was oriented to the rising point of the Pleiades. Bob Oldham Stones and Stars Project I have created a line of photo notecards of scenes in Portugal including many of the megalithis sites. Write bobtheham@igc.org for info.