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 Moon´s 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.
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S1 Llananno to Drygarnfawr cairns.

Southern Major Lunar Standstill alignments from S1 Llananno stone ring to Drygarnfawr cairns, Rhayader, Powys.

S1_Drygarn_12_Aug_1989.
Time- lapse photograph of the Moon setting on Drygarnfawr cairns at a southern lunar extreme in 1989 some months after the standstill of 1987.



12th August 1989

The first time- lapse 35 mm film photograph of the Drygarnfawr cairns with a moon set was secured in August 1989- 23 months after the lunar standstill of 1987.







06th August and 03rd September 2006

Two further photographs were secured in late 2006 after the standstill of that year which occurred in July.


S1_Drygarn_06_August_2006_netTime-lapse photograph taken from S1 Llananno to Drygarnfawr 06th August 2006.
S1_Drygarn_03_Sept_2006_net
Time-lapse photograph taken from S1 Llananno to Drygarnfawr 03 September 2006.






















Deriving declinations of horizon marks from photography of sufficient quality.

Close estimation of the declinations of the two cairns on the summits of Drygarnfawr may be derived from high resolution photography. Here we have three separate long exposure photographs of the Moon setting on Drygarnfawr mountain all taken from the same spot, at the centre of S1 Lananno stone circle, with the same camera and same lens on identical settings. The distance to Drygarnfawr cairns is 17.7 miles,(28.49kms).

Accurate layering or montage of the three long-exposure photographs.

S1_Drygarn_06_Aug_&_03_Sept_2006_net
Layered presentation of three time-lapse images on the alignment S1 Llananno to Drygarnfawr cairns.

The declinations of the two cairns may be extrapolated digitally from each of the photographs independently. When all three extrapolations agree to a resolution of better than one arc minute of declination then we can be assured that the cairn's declinations have been verified reliably.

Positional horizon astronomy by digitally surveyed photographs.

With the approach of digital surveys performed on good resolution photography we may circumvent several basic parameters of traditional spherical astronomical calculations. Taking the apparent diameter of the heavenly body at the moment of the photography- from USNO data- we have a precise scale with which to measure, horizontally, the arc angle of the entire horizon in a photograph. Using this system we need neither the azimuth of the points under scrutiny nor the elevation nor estimation of atmospheric refraction. Also, if any extreme cloud or terrestrial refraction effects are concurrent with the photographs they will be observable and directly measurable. In effect, if the photographs are taken at, or near, the dates which the alignment caters to, we are simulating the observing practices of the ancient astronomers at the correct times of day/night and, for the Sun, in the same season as the original establishment of the alignment.

S1_Drygarn_cairns_declinations
The declinations of Drygarnfawr cairns from S1 Llananno have been verified by three independent extrapolations from photography.

The declinations of the Drygarnfawr cairns.

We see that the upper limb of the Moon would settle in the notch by the east cairn when it has a declination deficiency, from the Southern Standstill, of exactly twice the mean diameter of the Moon.
Declination of East Cairn                    =   -28° 01' (When centre of Moon has this declination the upper limb sits in the notch.)
62.2'
Southern Lunar Major Standstill                  =    -29° 03.2' ......at 1825 BC.