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Glog Hill

S1, Llananno to Glog Hill lunar alignment, Mid Powys

W/7.2.1   Glog Hill, Dolfor is perhaps the largest Bronze Age barrow cemetery in Wales. Some nine tumulii are strung along this hill crest. W/7.2.2  Markers for the extremes of Cyclic Perturbation. Extrapolating from several time-lapse photographs taken a few months after the last Major Lunar Standstill in 1987 we see that two notches flanked by tumuli give accurate positions for the Moon´s upper limb at both perturbation extremes at the Northern Standstill in 1800 BC as seen from the stone block S1, Llananno. These tumuli bracket the full range of the minor wobble in the Moon´s orbit, W/7.2.3  Early warning feature. A third notch at the foot of the northern hill slope will provide an early warning allowing the observer several minutes to shift his ground so as to accurately 'lead' the first flash of the lunar disc into the upper notch for the maximal declination (e+i+p). W/7.2.4  Cyclic Perturbation - (e+i+p) and (e+i-p).

At a lunar site we should expect to find markers at either the foresight, on the horizon, or near the backsight which cater for the measurement of the perturbation wobble, (+&- p), to a resolution of better than 2 arc minutes of declination.   Without these installed a lunar site would be inoperable. Here on Glog Hill the two hill peaks on the northern end of the ridge are adorned with tumuli which bracket precisely the full range of cyclic perturbation at the Northern Major Lunar Standstill. The upper limb of the Moon, when rising near a standstill, will appear between these two tumuli allowing the astronomers to make an accurate estimation of the current condition of the lunar perturbation. Taking careful readings for several months prior to and after the standstill will furnish enough data to allow the current cycle of perturbation to be established and eliminated from the final calculations. which pin-point the day of the standstill.

W/7.2.4  Sighting to the centre of the lunar disc.

Although, here, the Moon at mean perturbation would rise with a large tumulus on the centre point of the disc this would not be a time to make the most reliable observations. Reading from the centre is not as certain as leading an upper or lower limb into, or out of, a notch. however this could serve as an optical check on the calculations derived from stake-setting positions for upper or lower limbs..

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