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.

Obliquity banks.

Obliquity banks or slopes employed as high resolution foresights.

Obliquity on Rhinog Fawr from Harlech S2
Obliquity on Rhinog Fawr from Harlech S2 standing stone.
A fine example of a dressed profiled stone drawing attention to the Megalithic Calendar alignment CIs 10 & 16 on Rhinog Fawr north slope.
In close studies of refined astronomical observatories in prehistoric architecture it has become clear that a range of management procedures have been employed to deal with the impact of the full glare of the sun on the observers' eye. An observer may, by stepping lateraly, bring the sun down behind a horizon feature thus reducing the visible disc of sun or moon to a very small sliver, yet still be confident that the fraction is in sight and the observing stance is verified.
Also fortuitous use of certain landscape features has been employed to increase the resolutions of an observation.
The most high resolving situations so far recognised are when the sun or moon rises or sets on a hill flank which precisely mirrors the Angle of Obliquity to the Ecliptic. This is the angle of tilt of the Earth to the plane of it's orbit and all celestial objects follow this angle as they move up or down over the horizon. Another distinct advantage to using an obliquity bank as foresight is to prolong the time the solar or lunar disc crosses the horizon fully by several multiples. The sun rises fully from upper limb to lower on a level horizon in about 3 minutes. When organised to rise over an obliquity bank it may take 40 minutes or more.

List of Obliquity banks natural and artificial identified to date.

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Ballochroy, Kintyre.

This image is synthesised from A.Thom's survey of the Ballochroy to Ben Cora, Jura alignment and photographs taken from behind the standing stone row at Ballochroy.
This was the first site to be recognised as a high resolution solstice alignment employing an obliquity bank.
to Bheinn Corra's northern flank, on the island of Jura.


Ballochroy
BallochroyThom

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