Glossary X
At a lunar backsight where permanent or temporary ancillary extrapolation gear has been set up there should be a length preserved between major stones which is the 4G for this site. This 4G represents, on the ground, the lateral distance an observer must move in order to 'shift' the Moon through the declination range K. K is the change in the MoonŽs position during the 24 hours preceding a standstill. At a Major Standstill it is 46.5 arc minutes and at a Minor Standstill 30 arc minutes. See also- K, ANGULAR DISPLACEMENT, EXTRAPOLATION PROCEDURE, LUNAR STANDSTILL.

The Thom Paradigm

S2_Glog_Hill_(e+i+p)
From the stance S2, Llananno stone chair the western flank of y Glog matches precisely the rising path of the lunar upper limb when the Moon reached a Major Northern Standstill with maximum Cyclic Perturbation circa 1800 BC. See S2 y Glog.

Since the publication of Alexander Thom's monograph 'Megalithic Lunar Observatories' in 1971 much debate has developed both on and of campus on the reality of high resolution solstitial and lunar extreme alignments deployed by prehistoric peoples in Britain.

The Debate

The general consensus of opinion resulting is that these ancient astronomers could not realise accuracies of better than 1° of arc angle in their observatory architecture. However the evidence in the field clearly demonstrates that these early astronomers must have managed to resolve- and so quantify- several librations in the lunar orbit much smaller than this imputed limit and also construct solar sites capable of fixing dates to better than half a days reliability.

Astronomy by spherical calculation.

Most investigators of Thom's thesis follow his approach which depends on spherical astronomical calculations based on theodolite establishments of the positions of backsights and foresights. However, from the initial observations of Sun positions by theodolite, through the geocentric conversions and corrections, then estimations of refraction pertaining 4000 years in the past, many unreliabilities may be introduced.

Astronomy by photography and high resolution digital draughting.

This website offers evidence gained from a complex of megaliths in Mid Wales never before examined. The data has been secured both by tradition spherical mathematics and. alternatively, by 35 mm film photography followed with high resolution digital surveys. The two approaches are entirely independent. With the digitally surveyed method there is no need to establish the positions of the backsights nor any azimuths of foresights. All necessary base data will be contained in the photography if good quality images are secured. Positional data for Sun or Moon at any moment of photographic imaging may be downloaded from the United States Naval Observatory Data Services...(USNO).
This approach- digital surveying of high resolution photography- may give positional data to sub- arc minute accuracies.
High resolution digital extrapolations to times past or future may be performed on the images in image editing software, if necessary. In thse studies we have recorded many instances where the Sun at a required declination sits cleanly on a distant prehistoric monument. Such images may not need further calculatory extrapolation, the intent is clear.
However if studies need to be based on near- miss photographs taken on solstitial or lunar standstill alignments then extrapolations might be plotted to positions plus or minus hours or centuries reliably.

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