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 and S2 Llananno central backsights for
the Llananno Megalithic Complex.

Sites S1 and S2, Brondre Fawr, Llananno.

Along two kilometres of Brondre Fawr ridge there are, or have been, a linear string of stone blocks. Some 10 are under examination for their potential as astronomical backsights
With extensive photographically verified calculation it is clear that the two stone blocks S1 & S2 are centrally positioned to support two astronomical formalities: (1) a Major lunar standstill observatory and (2) many divisions in the 16 epoch Megalithic Calendar
Of the 25 tumuli and cairns visible to the unaided eye from this place 19 support high resolution solar or lunar alignments from S1 and S2.

S1_&_S2_backsights
14 high resolution alignments emanate from S1 and S2 involving 19 Bronze Age tumuli and cairns in astronomical formalities.
The declination shift on y Glog, 5.5 miles distance, effected by moving between S1 and S2 is exactly 31.1 arc minutes- the mean diameter of the Moon.
All foresights have better than 2 arc minutes of declination resolution.

S1, Llananno, Brondre Fawr.

This carved rock cut seat faces east toward the concentration of tumuli supporting megalithic calendar alignments.
The surrounding stone ring has only a few remaining stones.
A ruined cairn lies at 30 metres distance to the south south- east.
front
Stone block S1 Llananno is a rock cut 1 ton block dressed to a shape similar to a horse- mounting stone. S1 Llananno sits at the centre of the highest stone circle in Britain. Little remains of the encircling ring.




S2 Llannano.

Weighing in excess of 2 tonnes this earthfast block is carved to an armchair or throne shape. When sitting squarely an observer's eye is directed to the largest Bronze Age cemetery in Wales strung along the crest of the prominent hill known locally as y Glog, Dolfor.
To_East
S2 Llananno is 2 tonne block quarried from a nearby sandstone outcrop. It is the largest free standing stone remaining on Brondre Fawr. Two more have been smashed or removed in recent years but their original positions have been recorded. S2 is marked as a parish boundary stone and is not yet a protected monument.
S2_to_y_Glog_net
From S2 to y Glog. Hill slopes found to parallel the Angle of obliquity would be great prizes for the horizon astronomer.
S2 was positioned to observe, on the flank of y Glog, the first flash of the upper limb of the Moon when at the furthest north point of it's orbit in 1800 BC -
(e+i)+p
See S2 to y Glog.

S2 to y Glog anchor alignment

From photographic extrapolation we see how the ancient astronomers capitalised on the fortuitously angled western hill flank of y Glog. This slope averages the precise curving path of the moonrise at the Northern Major Standstill allowing a mobile observer much extra time to adjust the spark of the lunar upper limb in the notches between tumuli and establish accurate stake settings.

Obliquity hill slopes

The angles of rise/set of both Sun and Moon throughout their cycles averages the Angle of Oblquity to the Ecliptic- the angle between the plane of the Earth's equator and the plane of it's orbit. There are many examples throughout Britain of the management of hill slopes which match obliquity for high resolution foresights
See Ballochroy to Bien a Cora, Isle of Jura, Argyll......Four Stones, Walton to Evenjob Hill, Radnorshire.....Thornborough Great tumulus to Castle Bank. Yorkshire.
S2_Glog_Hill_(e+i+p)_Survey_b
From S2 to y Glog. Hill slopes found to parallel the Angle of Obliquity would be great prizes for the horizon astronomer.

Parallax relationship between S1 and S2

Once the alignment S2/ y Glog/ northern lunar extreme had been established the position of S1 would be determined at a distance to the north giving exacly the stance for one lunar diameter difference from stone S2 on y Glog.
From simultaneous photographic studies the declination difference on y Glog between stances S1 and S2 has been found to be exactly one mean lunar diameter... 31.1 arc minutes. A probable function for this would be the estimation of lunar parallax by gauging the condition of current Apparent Diameter of the Moon.
S1_to_S2
S1 and S2 are 223.86 metres apart or exactly 270 Megalithic Yards.
223.86 metres = 270 Megalithic Yards. This is the step- aside distance to effect a declination change of 1 lunar diameter, (31.1'), on a horizon at 8.85 kilometres, (5.5 miles).

Method for estimating current lunar parallax at, or near, a lunation.

S1_to_S2_dec_shift_net
S1 and S2 are 223.86 metres apart or exactly 270 Megalithic Yards.
This distance is precisely the step- aside length required to displace the Moon rising on y Glog hill by it's own diameter. This feature could allow accurate measurement of the Change in apparent diameter and hence Lunar Parallax
Two observers #1 at S1 and #2 at S2 standby near a lunar extreme to observe the full moon rise.
Observer #2 will 'catch' the first flash of the upper limb and,- by moving lateraly,- 'bring' the flash into a notch or onto a tumulus and set a stake at that point.
Observer #1, a few minutes later, will then 'bring' the lower limb of the Moon down onto the same foresight and set a stake when perfectly aligned.
When the two stakes have been set their relationship to the fixed markers S1 and S2 can render the sign of current parallax and the magnitude.
If the stakes are outside S1 to S2 then parallax is negative...the Moon apears smaller than average.
If the stakes are within S1 and S2 then parallax is positive...the Moon appears larger than average.
Also the magnitude of the current parallax may be estimated by measuring the distance of the stake positions from the stone markers S1 and S2...In good weather conditions these should be equal.
This data would be essential for the subsequent calculations to be employed around the standstill necessary to locate the exact day of the ultimate extreme.....


Dual solar alignments.

S1&S2_to_Warren_net
The mean apparent diameter of the Moon- 31.1' - is very close to the diameter of the Sun- 31.6'..
On horizons at a similar distance as y Glog double observations of sunrise might be managed. If an alignment from S2 to the solar upper limb has been established then an observer at S1 will see the lower limb graze the same foresight a few minutes later

Multiple tumuli to the east of Brondre Fawr.

Crown_Estates
The Crown Estates high ground carries several megalithic calendar foresights for alignments emanating from S1 and S2 stone chairs.