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Megalithic Calendar 5

Refraction and practical solstitial observation.

2.5.1  However despite the superb engineering standards of the Ballochroy/ Jura alignment no modern astronomer, Thom included, would consider this to be a reliable method of deciding the day of a solstice. Even in Bronze Age times the clarity of weather could not have been regularly stable enough to give identical, mean, refraction values for the three necessary evenings around a summer solstice. Today it is known that refraction values may vary by nearly half of a degree- 30 arc minutes in 24 hours. An alignment with an engineered tolerance of less than 1/150th of this could not be expected to function regularly when unpredictable values for refraction are involved.

Identifying the solstice in retrospect.

2.5.2  Thom, along with other archaeoastronomers, has proposed that a simpler system was employed to ascertain the day of a solstice and, if we consider the possible use of the cist position at Ballochroy and the structure of the Megalithic Calendar, it seems likely that the megalith builders did employ other, more practical, tactics for identifying the true solstices. If the astronomer was to use the cist at Ballochroy as backsight, halving the elapsed 14 days between two sightings of the emerald flash on Ben Garridale and Corra Bhienn, (see Calendar 4), then a somewhat more reliable system might be considered. The daily movement of the Sun 7 days short of a solstice is still only 3 arc minutes but it is a quantity less easily swamped by unmeasurable refraction values. Choosing days at a further distance from the solstice when the Sun is making yet greater daily changes in declination would be an even more pragmatic approach. At 23 days from a solstice the Sun is making a daily declination change of about 8.5 arc minutes and many alignments have been identified which fix these dates on either side of both solstices, winter and summer. These are Calendar Intervals 4 & 6 with the Sun at declination 22 deg.3.6 min.

2.5.1  Two recently identified Mid Wales precision alignments for Megalithic Calendar intervals 4 & 6.

The Sun is very near the declination for Calendar Intervals 4&6. The importance of this alignment is carefully indicated. The size, profiles and positions of the two stones are arranged to allow the shadow of the forward stone to sit precisely on the stone to the rear at sunset on the two appropriate days of Megalithic Calendar Intervals 4 & 6, usually 2nd June and 12th July today.

Sunset alignment Four Stones, Walton to tumulus 1, Bache Hill.

Sunrise alignment from S1, Llananno to Two Tumps, Dolfor at declination for CIs 4&6.

2.5.2  The symmetrical arrangement of the Megalithic Calendar epochs around the solstices.

In the Megalithic Calendar this was the position of the Sun at the four Calendar Intervals surrounding the summer solstice, nos. 4 & 6and 3 & 7. The calendar appears to be arranged so that there are two 23 day epochs on either side of each solstice. If the Sun was obscured at either of these first flanking dates then the observations made at the ensuing dates, nos. 3 & 7 say, could be used with equal accuracy so long as the count of days was strictly kept.

Over- engineering. 2.5.3  If such a reliable calculatory method of finding a solstice is inherently available in the organisation of their calendar why did these engineers squander so much time, effort and community resources on solstitial monuments which are amongst the heaviest and most impressive in the British Isles? Stonehenge, Wiltshire, with it's summer solstice marker- the Heel Stone- could never have been a practical solution to the task of identifying the true day of the solstice. The length of the alignment, some hundreds of feet, is too short to furnish a discernable step- aside distance representing the 12 arc seconds declination change from the day before and day after a solstice.

Summer solstice alignment from the centre of Stonehenge Ia circa 3000 BC. 2.5.4  This survey is based on a photograph taken at a summer solstice in mid 20th century AD from the centre of Stonehenge at a height of 5.75 ft above the present soil surface. The distance to the Heel Stone is less than 300 feet, (91.5m). For such a short alignment the step-aside distance which would represent 1 arc minute on the Heel Stone must be around 3 inches, (76mm), about the distance between the eyes of a 6 foot observer. Even if we impute that there might have been some structure at the centre of the ring, like the holed stone at the Rollright stone circle, which fixed the observing position of the eye it would need further calibrating marks less than 15mm apart, to resolve the movement of the Sun in 24 hours at a solstice. This problem illustrates why reliable solstice observations cannot be made by observing the length of shadow cast by a gnomon no matter how tall.

Stone 97.

2.5.5  A large stone hole, (stone 97), has been identified about 10 feet, (3 metres), to the left of the present outlier, the Heel Stone, at Stonehenge. It is theorised that this hole held another large stone or possibly have been the original position of the Heel Stone. It can be seen that the first flash of the Sun over the horizon appeared in the notch which would be created by the vertical side of stone 97 cutting the horizon. The backsight was then the centre of the Aubrey Hole ring, Stonehenge Ia, believed to date from some centuries before 3000 BC. This would have been a difficult foresight considering the low altitude of the horizon and proximity of the middle ground to the line of observation. Sometime in the early history of the monument this alignment may have become regarded as unsatisfactory and the Heel Stone moved to the right allowing the fully risen solar disc to sit neatly on the top of the stone. The increased altitude would free the line from most refraction and distortion problems. It would also present a clearer image to large crowds of people assembled within the ring whereas in the former position the first flash would have been obscured, to the left, by the indicator stone. It should be kept in mind that, at the date of the establishment of Stonehenge 1a there has been found little evidence for large stones in or around the Aubrey Hole circle and the views from the centre were probably unobstructed with only the Heel Stone as a possible horizon marker.

Horizon foresight for the Heel Stone alignment. 2.5.6  Even if a now- vanished structure on the horizon behind the Heel stone is imputed this horizon is less than 3 miles (4.8 km) distant which limits the step - aside distance representing 12 arc seconds to only 2.5 feet (0.75m) at the backsight. Even if we surmised that there was formerly, somewhere at the centre of this monument, a slab bearing carefully kept incised marks displaying the necessary stances for solstitial observations it would still appear impossible to depend on such an arrangement. A glance at the terrain over which the Stonehenge summer solstice line runs shows that this line has little or no altitude and never clears the intervening ground sufficiently to be free of greater refraction problems incurred by erratic heating and cooling of the local ground. Compare this line with the Ballochroy Stone Row line to Corra Bhienn summit. This stone row sits some 82 feet (25m) above the waters of the Sound of Jura and less than 100 feet (30m) from the water's edge. Across this empty span of seawater the line rises to over 1500 feet (457m) to the peak of the mountain removing it from local terrestrial refraction problems. This situation is typical for nearly all of the high resolving sites under study and shows how carefully these observatories were placed in the landscape. Cultural redundancy. 2.5.7  Stonehenge does not have these topographical advantages yet enormous resources were expended over 1500 years at this place on several major and minor rebuilding programmes. It is suggested that Stonehenge may have been the equivalent of a megalithic national science museum or filled the function of the Old Greenwich Observatory- originally the foremost observatory in Europe but later superseded as a high resolution observatory and became a place where the history and essentials of astronomical science might be displayed to a general populace but no longer a reliable, state-of-the-art practical observatory.

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