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The Modern Antiquarian Forum » Something completely different |
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nigelswift 8112 posts |
Apr 21, 2005, 09:13
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I think I've posted a link to this amazing site before… http://www.megalithicsites.co.uk/horast2.html One particular thing struck me: "By taking particular care in their choice of foresights the ancient astronomers could prolong the setting of the Moon by several minutes. These critical extra minutes allowed the observers the extra time to shift their ground and so ´move´ the Moon precisely into the bottom of the notch. This specific place of observation was then marked by driving a stake into the ground at the observer's feet. This observing practice would continue night after night with a fresh stake driven at each observation until a curve had been described on the ground." … To me, the implication would be that (maybe) some arrangements of stones weren't intended for single observations but were determined by "tracking" observations as a result of the observer moving his position. If there was anything in this it would open up a huge field of observation (and argument…) at lots of sites. Callanish springs to mind, and double rows, and maybe even circles. Is this old hat? Any comments?
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FourWinds 10943 posts |
Apr 21, 2005, 09:24
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One comment I have on this is that doing so does not automatically result in a circle or curve. You could draw a straight line on the ground and walk along that marking the spot where the alignment is apparent. This could actually explain some stone rows that don't point at anything, but are in places where obvious 'sighting' points lie in obvious directions. I don't know of anyone else who's considered rows and alignments with this in mind. I've started to study a few stone rows in this manner and have some ideas about a couple of them, but more time is needed. To make a curve or circle you would have to tie another pole to the positioned one and then move with the string taut to get the spot for your alignment. If you tried to do the curve thing by eye you would almost certainly end up with an elipsoid thing. But many stone circles have equal spacing and the technique above wouldn't create that. Also, it can't be applied to the vast majority of Irish stone circles as they conform to patterns - 5, 7, 9, 13, 17 stones etc. Maybe some of the Scottish or Cumbrian ones fit the format?
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StoneLifter 1594 posts |
Apr 21, 2005, 10:07
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It's all hyper-theoretical. The practical constraints are the weather and tiredness. Will read article and get back. Hope to study those Thornhope rows a bit more this summer. There may be another short row higher up or it may be a chance collection of erratics - looking at that too. Hope to capture some of these moon movements on film (obviously dreaming). Setting up cameras and saving for filmstock. Neil Young has a well-received 8mm film of Greendale. One critic said it was 70% out of focus - seems like a good result ! (He was using super 8 - Std 8 is steadier - allegedly). Eclipse ! Eclipse ! Eclipse !
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greywether 241 posts |
Apr 21, 2005, 11:06
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Haven't read the link in detail, Nigel, but will later. I think that, for what you are suggesting to work, the setting positions of the moon as seen by the observer would have to move from day to day in a way which corresponds with what the moon is actually doing. But the observer doesn't necessarily see what the moon is really doing because of the effect of refraction. Here are some quotes from Douglas Heggie's "Megalithic Science". "[Refraction] makes the apparent altitude of a rising or setting body higher than it would be in the absence of the atmosphere by an amount which can exceed the apparent diameter of the full moon. .... Atmospheric variations vary from night to night, and the resulting variations in refraction would have limited the usefulness of very accurate orientations even in megalithic times. In other words, unless conditions then were much more stable than they are now, these variations impose a limitation on the accuracy with which a fixed megalithic orientation could have been used to record a fixed astronomical position. ... Refraction is particularly subject to variation just above the level of the ground ... [distant foresights] tends to make refraction stronger than it would be otherwise. Perhaps it also implies that the declinations defined by these lines can now be determined only with added uncertainty, and that their possible use in megalithic times was rendered particularly troublesome." As an example, he adds "... refraction changes would have prevented the use of the accurate natural foresight at Ballochroy, Argyll from determining the day of the solstice since they much exceed the daily variation of the declination of the sun at the solstice." In other words, what I'm saying is that refraction is not simply a problem to modern day surveyors trying to measure and replicate what was seen in the past. It was also a problem to those trying to observe and record movements in the past if they were trying to achieve highly accurate recorded positions which they could return to a year later or whenever and expect to see the moon or sun in exactly the same place as it was when the recorded position was set up. I'm not anti-alignment; just unconvinced by many of the claims for very high accuracy.
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nigelswift 8112 posts |
Apr 21, 2005, 11:27
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I'm not anti-alignment; just unconvinced by many of the claims for very high accuracy. Agreed. But of course a gap between rocks that casts a soltice sunbeam still works tolerably well. If they wanted absolute accuracy maybe they'd have kept with sticks rather than great big lumps of rock - which is why the whole thing strikes me as more likely to be symbolic rather than of specific use. The collection of pepper pots in my bay window tell me the time of year as accurately as Stonehenge... But stones do work tolerably well. If you stand with your back against the northernmost stone of any circle you've got a pretty usable calendar. And clock.
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FourWinds 10943 posts |
Apr 21, 2005, 11:53
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What kind of accuracy you after? http://www.knowth.com/loughcrew-equinox-mar05.htm
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greywether 241 posts |
Apr 21, 2005, 12:05
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Yup. Something that produces roughly the same effect on 5 or 6 days of the year will do me :-)
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nigelswift 8112 posts |
Apr 21, 2005, 12:46
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Accuracy is determined by the narrowness and length of the opening. If it's thin and long you can get a Knowth effect that suddenly switches on and lasts about 2.5 minutes in one spot and then switches off (being the travel of the sun across it's own diameter at midday - maybe twice as long early or late in the day). I guess that's the limiting factor to accuracy. (Although I think you can track a shadow more accurately).
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greywether 241 posts |
Apr 21, 2005, 14:12
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We've moved to considering accuracy when the sun shines through a construction from the point where you started which was an observer looking out to the open sky with only hills as framing references. Nothing wrong with that but different considerations apply. Can I go back to the open sky point and try to expand on what I mean by "accuracy" since it's not a very accurate word! I'll use Ballochroy which is described here but it's really a general point. http://www.megalithicsites.co.uk/Calendar4.html Some have claimed that sites like Ballochroy were used to predict the summer solstice with the calendrical precision that we now take for granted. In other words, using Ballochroy they could tell the date we now call June 21st (say). My point was that refraction means you cannot do this. Some years it might work and in others, because of refraction, you could get the date we now call June 22nd or 23rd. You can apply the same point to any so-called predictive sight line. So I have a problem with that line of argument. However, and this is my main point, determining what we now call June 21st may not have been the point of the exercise. If the point was to determine when the sun turned in the sky, then Ballochroy is accurate (when taken in the context of the conditions that applied at each annual observation). If something had to be done by the community to mark that point, the observers could tell them the appropriate day. Perhaps the actual observation was just as an important part of the process as the activities which followed. So, if these sites were used simply to observe when something happened in the sky, that's good enough for me. And I don't need convincing about the alignment qualities of the different sites which usually come into these discusions. I bought that one a long time ago. However, I do remain highly sceptical about those arguments which claim that monuments were used to determine events with an accuracy equal to that which developed with the growth of astronomical knowledge several millennia later. Especially when doing so involves sightings that can be affected by refraction. And, talking of the sun, thats enough of this for the moment. I'm now going out to enjoy it!
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