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Megalithic Calendar 2

2.2.1.

1.1 Astronomical Bases of Calendars The principal astronomical cycles are the day (based on the rotation of the Earth on its axis), the year (based on the revolution of the Earth around the Sun), and the month (based on the revolution of the Moon around the Earth). The complexity of calendars arises because these cycles of revolution do not comprise an integral number of days, and because astronomical cycles are neither constant nor perfectly commensurable with each other,

From 'The Explanatory Supplement to the Astronomical Almanac, P. Kenneth Seidelmann, editor,

The elliptical orbit of the Earth. 2.2.2  Although the finished construction of the Megalithic Calendar is impressive, it's existence must presuppose yet greater achievements in astro-mathematical modelling than a solution to the leap-year cycle. To attain the fine symmetry of this 16 partitioning of year the megalithic astronomers had to recognise and surmount problems incurred by the fluctuating speed of the Earth in it's orbit around the Sun caused by the assymetry of the perihelion/aphelion cycle. 2.2.3  The orbit of the Earth is not circular with the Sun at the centre. It is elliptical with the Sun sitting at one of the foci. This means that the Earth must 'climb' for one half of it's orbit away from the Sun and 'fall' toward the Sun for the other half. At perihelion, closest point to the Sun, the Earth is travelling fastest and at aphelion, furthest point, it is moving slowest. Perihelion occurred in mid-20th century AD near the winter solstice, in January, resulting in our winter half of the year being 7.5 days shorter than our summer half. The elliptical orbit of the Earth is precessing slowly and the perihelion/aphelion cycle is moving continuously with relationship to the solstice cycle. In 4040 BC perihelion coincided with the autumnal equinox and the two halves of the year had the same number of days. The Megalithic Equinoxes. 2.2.4   In 1800 BC the winter half of the year measured 4 days shorter than the summer half and hence, today, if we wish to verify a megalithic equinox alignment, we must ascertain that the observatory identifies two specific dates in the year: both the day after our spring equinox and the day before our autumnal equinox. This arrangement, in 1800 BC, lengthened the winter by two days and shortened the summer by two days bringing the two halves into symmetry by the count of days. In this, as with several fine adjustments unique to the Megalithic Calendar, the archaeoastronomy student may positively identify the work of the astronomers of the Middle Bronze Age. Establishing single foresights for dual declinations. 2.2.5  In the construction of this ancient calendar the astronomers had first to establish the days of the true solstices, winter and summer. They would make careful observations of the turn-around of the movement of the Sun on the horizon both north and south then count the days that the Sun took to move from one turn-around position to the other. See Ballochroy Stone Row, Kintyre. At this stage the megalithic astronomers would detect the change in speed of the Earth in it's orbit. In the attempt to further divide the year into smaller symmetrical parts they would be presented with difficulties which might have raised interesting speculation on their world views. See Megalithic Mathematics 1. In order to establish their version of the equinoxes, by halving the count of days between solstices, they would find that the Sun did not return to exactly the same point on the horizon in the same number of days after a summer solstice as after a winter solstice and that it's seasonal movement is not symmetrical. The seasonal discrepancies between these two positions meant that, around the equinoxes, two foresights for two corresponding dates, some 13 arc minutes apart, would be required,- one for one season and one for the next. 13 arc minutes is nearly a semi-diameter of the solar disc, (32 arc minutes) and the Sun is making daily movements of 24 arc minutes at this time of year. This would give rise to some confusion in establishing the correct date if only one pin- point foresight is employed so we find that foresights for dates at or near the equinoxes may be constructed in pairs or with some feature at the foresight which brackets the range of possible declinations as in these examples:

2.2.6

Bracketing foresights. Here each alignment is shown with the two maximal errors, plus and minus, which could occur when the sun reached it's required declination 12 hours distant from the moment of rise or set

Lechwedd Penrhiwen, Rhayader. The intersection of the two hill flanks hold the Sun when sitting at semi- diameter on the horizon.

Brook Cottage, Llananno. The linear bank, set at right angles to the line, defines the semi- diameter of the Sun on the horizon.

S2, Llananno/ Warren Hill. The semi- diameter of the Sun is defined by the tumulus on the left and the hill notch on the right.

S1, Llananno/Gorslydan,

2.2.7

The two tumuli are arranged to frame the disc when the lower limb sits on the horizon with the Sun at the precise, mean declination for these Calendar Intervals.

S2/Warren Hill

2.2.8

The framing here is performed by the tumulus on the left and the intersection of the flanks of Warren Hill and Beacon Hill behind. When the semi-diameter of the sun sits on the horizon between these marks it is at the exact declination for the nearest intermediate calendar date to the equinoxes. Although only one tumulus is involved in the S2/Warren Hill alignment it can readily be seen from this photograph how clever use was made of the small, steep notch provided by the flank of the tumulus. Arrangements such as this provide a catchment for the emerald flash at near right- angles to the path of the Sun and several examples have been photographed in action in Mid- Wales. For more on inclined notches see html page Horizon Astronomy 4,

It should be noted that these CIs are equinoctial or the next nearest to the equinoxes and the daily movements of the Sun is still large- nearly 24 arc minutes- so we should expect to find twin marks bracketing the broad range of possible declinations at the foresight. At all these sites the foresight range is centred on the mean ideal declination for the two positions whilst throughout the rest of the calendar, when the seasonal discrepancies are smaller, the mean of two close declinations have been indicated in single pinpoint foresights. Calendar declination pairing summer with winter. 2.2.9  Further evidence that the megalithic astronomers understood perfectly the asymmetry of the Sun's movements throughout the year can be seen when comparing the dual declinations required in the autumn/winter seasons with the spring/summer seasons. Apart from the solstitial and equinoctial declinations the two sets are not mirrored. This we should expect as Earth is travelling faster in the autumn/winter and the equinoctial four day adjustment must be reflected.

Thom, Megalithic Sites in Britain p110 Table.9.1.

	spring&summer	---	adjustment	---	Autumn&winter
	CI 5 summer solstice	+23deg 54.3min	(0min)	-23deg54.3min	winter solstice CI 13
	CIs 4 & 6.	+22deg3.6min	(12min)	-21deg51.6min	CIs 12 & 14
	CIs3 & 7	+16deg40.2min	(24.6min)	-16deg15.6min	CIs 11 & 15
	CIs 2 & 8	+9deg 9.6min	(42min)	-8deg 27.6min	CIs 10 & 16
			+0deg 26.4min. CIs 1 & 9 Equinoxes

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