Calendar and Clock Systems and the Early Phases of Stonehenge

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It is evident from the design inherent in the Stonehenge structure that its builders had a working concept of the 360˚ circle. Hand measurements are used by nomadic societies still today in land navigation techniques. 1 finger is equivalent to 1 degree, and a circle made around the body totals 360-fingers. Here we have not only a universal, but also, a physiological basis for the 360˚ circle. By projecting this onto the sky and landscape the ancients were able to form the concept of altitude and azimuth positions of celestial objects.

Through continued observation they would have noticed a seasonal cyclic anomaly in the gradual shift of the sun against the position of the stars, the difference between the side-real and tropical day.

SH clock and calendar orion sun winterSH clock and calendar orion sun spring

SH clock and calendar orion sun summerSH clock and calendar orion sun autumn

If we record the position of the sun against a fixed reference point in the stars it has the effect of giving the sun the appearance of gradually shifting in an anti-clockwise direction around the horizon over the course of the year. The number of days from position to position is roughly equivalent to the amount of degrees it has traveled around the 360˚ circle. On the winter solstice solar-midnight and mean-midnight coincide. At this exact moment the sun will be on due north, under the horizon if  you are in the northern hemisphere (in the southern hemisphere it will be solar noon) and Orion will be due south.

Because the earth moves 1˚ each day in its orbit about the sun, the amount of days that it is from winter solstice is equivalent to the amount of degrees the sun appears to shift. After 90 days the sun will appear to have shifted 90˚ in an anti-clockwise direction against the horizon. 90 days from winter solstice is roughly spring equinox, the sun will now be due west when Orion arrives back at due south and instead of happening at midnight this will now occur at 6pm in the evening. This of course means that, for example, a shift of 1 quarter of the 360˚ circle is equivalent to one quarter of the year and results in a time shift of one quarter of the day. In this seasonal cyclic pattern is the foundation of the calendar and clock systems in use still today.

Perhaps the most underappreciated human invention is the-minute-into-the-hour. The stroke of genius came when someone established that 1˚ would be equal to 4 units of time, and this unit would be called the minute. If there are always 4 times the amount of minutes than degrees then it can always be said that a complete day is equivalent to 1440 minutes. However many hours there are in your time-system you simply divide 360 by that figure to arrive at how many degrees your mean-sun will travel per hour and then divide 1440 by your amount of hours to arrive at the figure of how many minutes there are in your hour.

The earth moves 1˚ in its orbit about the sun each day which ultimately causes the difference between the sidereal and tropical day and the ancients could now measure this difference. By establishing that 1˚ is equivalent to 4mins, the ancients could say the stars rise approximately 4mins earlier each day, and this is the tool which led people to mean time. We can see in the developmental stages of Stonehenge how the-minute-into-the-hour became of greater use, from the transitional designs of one phase to another.


SH phase 1 clock and calendar


Stonehenge Phase 1 occurred circa 3000bc and saw the bank raised, ditch dug and the erection of 56 posts. It is suggested that 2 posts acted as 1, or that one position consisted of 2 posts. The circle would have 28 total positions this is based on the resulting calendar of 364 days a year. You could multiply 6.5day weeks by 56 and arrive at the result, but you could just as easily observe the halves on the same day i.e. you observe sets of 13 day weeks, 13*28= 364. As there are 13 lunar orbits in one year this would give the calendar a lunar association, the 28day month is very close to the 27.27 days it takes the moon to orbit earth. Of course, the premise is that the ancients sought a unified calendar and time system. In this system they achieved a certain equilibrium, the hours in the day, days in the month and weeks in the year are all 28. Also the days in a week and months in a year are both 13. Following this calendar would have meant 3 years of 364days and 1 year of 369days, giving 5 additional intercalary days in the last year compared to the their standard duration.This arrangement totals 1461days which we observe in the modern era as 365days a year*3+1 year of 366days = 1461 days.

If we consider again the sidereal and tropical day variance, and that 1 day is equivalent to 4mins shift of the apparent position of the sun against the stars, then each year with 1.25days missed off of the calendar, they were suffering 5mins variation to their time-system for the entire second year, by the 3rd year it was 10mins out and for the fourth year it would be 15mins out until they had their intercalary festival which likely took place at the end of the year. The change year to year would have been particularly hard to track with this time and calendar system because of the resulting degrees and minutes per hour. Where there is uniformity among the days, weeks and months, the degrees and minutes were split to very large decimal positions.

360˚^28= 12.85714285714286˚

1440mins^28= 51.42857142857143mins

These would have been extremely difficult figures to work with, however, multiplied on divisions of 4 they add up to equal numbers. It seems that at the stage of Stonehenge phase 1, initially the degrees-and-minutes-into-the-hour were of less importance, or were regarded as such, and greater emphasis was put on uniformity across the days, weeks and months of the calendar and time system. With the resulting time-shift of 5mins per year and the complexity of the divisions to decimal places for degrees and minutes, rather promptly the 28hr day was abandoned in favour of a new system that still afforded unification across the calendar and time system, but also resulted in even division for the degrees-and-minutes-into-the-hour, this was the 30hr time system.


Stonehenge Phase 3a

SH Phase3a


Stonehenge phase 3a, circa 2, 500bc, saw the erection of the sarsen stones in the Outer Circle and Great Horseshoe, as we see the remains of today, but the initial bluestone layout was very different. The phase 3a bluestones formed an opposing horseshoe also centred on the summer solstice axis. Inherent within this overall design were the main elements that make up the calendar and time system that would be used at the site for the next 1000yrs.




The calendar would be transformed from a lunar cycle of 13 months a year to a solar cycle of 12 months a year. 30 pillars would represent the 30 days of the month, giving 12 months a year totaling 360days and requiring 5 intercalary days each year and 6 in the 4th year. This model should look familiar because it is very similar to our own calendar. A marker could be moved each day to record the month, and as 30^12= 2.5, each month a marker could be moved 2.5 places, resulting in the alternate movement from a gap to a pillar centre.  Because each section runs from gap to gap, the centre of a pillar is the centre of its section. Starting at the north gap for the winter solstice the marker would jump two gaps and land at the centre of the next pillar for the next month. If the marker is moved in an anti-clockwise direction, then by month 3 the marker will be on the west position.

SH clock and calendar right-angle N-W

This process would echo the sun/star displacement where the sun is due west for the spring equinox sunset at 6pm and Orion is back on due south.


SH clock and calendar orion sun spring


The weekly calendar encoded at Stonehenge is 7.5days a week, 48 weeks a year giving 360days. As 70% of 7.5 is 5.25, include the intercalary days and the intercalated 0.25 of the day, and they were following 7.5*48.7= 365.25. It is likely the 0.25 was combined in the 4th year as an extra intercalary day. Meaning the calendar would result in a 1minute shift each year, totaling 4minutes over the 4 years and which is reset in the 4th year by the extra day. This again is the process we follow in the modern calendar with the use of the leap year.



SH clock and calendar dimensions

Stonehenge phase 3 was built the way it was, partly to enable the easy conversion of degrees into minutes. The monument design totals 300ft, over 360˚ gives 1.2˚ per foot. As there are 12inches per foot then an inch (adult male’s thumb width) at Stonehenge is equivalent to a 10th of a degree as a land measurement (a finger width is equivalent to 1˚ as a sky measurement). As there are 4mins per degree in the mean time system format, multiplying degrees by 4 converts them into the number of minutes they represent. In this way Stonehenge is the calendar, the calculator and of course the clock.


SH clock and calendar sundial and pillar trimming


The Stonehenge earth clock has been described in depth already on this blog in the post ‘Stonehenge: a proto-sundial with bias toward summer’. A sundial face is configured into the north half of the circle and the hour positions are struck by a strip of light and shadow from trilithons 4+1 respectively. The calendar and time system is unified, there are 30hrs a day and 30 days a month, there are 12 months a year and 12˚ movement of the mean sun per hour, there are 48 weeks a year and 48 minutes per hour. In this system the number of days in a week, 7.5, doesn’t have a match. It is likely the same process was used, the .5 of the day was observed on 1 day giving an overall set of 15days, which is equivalent to half the hours in the 30hr day. A marker could have been moved across the pillars and lintels that make up the Great Horseshoe to track this as there are 15 total stones, 24 of these would give 360days. Which brings us to the next point, the number of weeks in the year would also be uneven in this system as it would require the 5 intercalary days, or to say that 48.7 weeks results in an uneven amount in any case.


SH clock and calendar1


The phase 3a bluestone arrangement also highlights how the ‘summer solstice’ axis is a fundamental part of the sundial. This is the position that the T1shadow strikes at solar noon. We can see here that T1 runs parallel to the stones making the channel in the bluestone horseshoe. This has the effect of causing the T1 lintel to run parallel to that axis and align to the position marking 15SP even where the shadow length varies in summer and winter. The true purpose of the summer axis alignment is glimpsed here, consider that the latitude of Stonehenge is 51˚N and the solstice axis is 48-49˚. Now consider that the gnomon on a horizontal sundial is angled at the latitude of its location. The Great Horseshoe position on the summer solstice axis is an approximation of this technique on a 2D plain. However, it doesn’t achieve the same effect as a horizontal sundial with angled gnomon.


SH clock and calendar east bluestones sun angle

The design of the phase 3a bluestone horseshoe confirms aspects of earth clock theory. The pillars run parallel to the direction of sunlight when the sun is at their position. As the above diagram shows, when the sun is at 90˚ due east the light travels straight across the land, and will be running perpendicular to the face of pillar 4 on the east, this is precisely what the stones in the bluestone horseshoe are doing. The position of Trilithon 4 blocks the light from hitting the circle on the other side which would mark 7.5SP.


SH clock and calendar 80az strike


The bluestones that are in the region of 80˚az, marked by the yellow line in the diagram above, show the angle of sunlight for this position and it can clearly be seen that light hitting the circle at that angle will result in a hit for position 7.5SP, the centre of pillar 19. As the sun is at 80˚az at 6am on May 5th, and 7.5SP converts as 6am 24hr time, this demonstrates that the monument is calibrated to May 5th, the date half-way between spring equinox and summer solstice. This gives the monument a bias toward summer, where it reads late but is more accurate, in winter it reads early but is more inaccurate. Although this sounds strange at first, in actuality it is rather similar to the modern practice of switching to daylight savings time. We obscure mean time to suit our societal needs, we throw the clocks forward for summer and then back for winter. Around late spring and early autumn Stonehenge time starts to read very close to daylight savings time.


SH clock and calendar dimensions

Stonehenge encodes myriad information within its structure. Take the average pillar and gap width, convert them into degrees, put them together and multiply by 30 and you get 1461.6, obviously encoding the number of days in the true 4yr cycle. Use 1.2 to convert between degrees and feet, but divide 1ft by 1.2 and you get 0.8333333ft. A third of the earth is 8333.3333miles. If we considered each section as 8.33333 long feet, then there would be 14.4inches in each long foot and 250 total long feet in the circle. 14.4 is an echo of 1440 minutes per day and 250 is a hundredth of the nearest whole measurement for the circumference of the earth, 25,000miles. We might even consider that the mile was picked specifically as a 25,000th of the earth circumference, putting it on the quarter sequence with 0.25 degrees per minute.

About The Great Circle

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