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 Rhosgrug I twin tumuli,
Crown Estates, Llananno.

High precision alignment from S1 carved stone block at the centre of Brondre Fawr ridge stone circle to Rhoscrug I a&b, twin tumuli, indicating the exact centre of the Sun when rising on Megalithic Calendar intermediate intervals nos. 10.5 and 15.5.- which occur in the Gregorian calendar @ 15th February and again @ 27th October.

Rhoscrug I a&b Bronze Age Twin Tumuli, Crown Estates, Lanbister.

Rhoscrug I a&b
Rhoscrug I a&b, Llanbister.
One of the high hills on the Crown Estates, Llananno. A typical Mid Wales moel-a round-topped symmetrical hill. Several of the highest tops on these Crown properties are adorned with one or more earthen tumuli. The bed stone of this area is friable Silurian/Ordovician mud-stone and very little rock is exposed as even the highest hills have a covering of boulder clay. The only available materials for mound building is this clay and turf stripped from the nearby hill-side.

Rhoscrug I a&b Tnail
Rhoscrug I a&b, Llanbister. These two well preserved earthen tumuli are constructed with skirts nearly touching. Both are within an arc minute of the ideal declination for CIs 10.5 and 15.5.

Rhoscrug I OS
Rhoscrug I OS. As with all of the hill top tumuli groups in Llananno these tumuli are located on the exact summit of the hill.

Sunrise 15th February, 1990.

At this moment the Sun's position is less than 5 arc minutes short of the ideal required declination for Megalithic Calendar Intervals 10.5 and 15.5.
Required dec. = -12° 39.6'.
Dec. at 07:30 hrs = -12° 44.5'.
Required declination was reached at 13:30 hrs on the same day.


Sunrise 15th February, 2002.

Cloud on the horizon obscured the first light on this morning. However after 15 minutes the Sun cleared the clouds allowing several images to be secured.


Survey of images from 15th February 2002.

Direct extrapolation from the layered images secured may trace the Sun's path back to the horizon.
The ideal required declination for CIs 10.5 and 15.5 of -12° 39.6' was attained at 10:00 hrs...2.5 hours later. Here we see that the path straddles the tumuli in close agreement with several photographic studies in other years.