On 12/6/12, Henry Baker <hbaker1@pipeline.com> wrote:
Does anyone here know what the fundamental _period_ of the antikythera device is?
I.e., by all reports, this device is a "planetarium in a box". So how many years of simulated time does it take for this device to return to its initial configuration ?
The known gearing, along with the number of teeth in most of the known gears, is described in detail here: http://cs.iupui.edu/~tuceryan/pdf-repository/Edmunds2011.pdf Apart from the sun position, which is a base unit of your question ("how many years..."), the known/proven functions are moon position and phase, saros x4, eclipse prediction, and exeligmos. All of the other stuff (metonic, olympiad, planets, etc.) is speculative and/or based on gears of unknown size. But the stuff we know for sure includes these named gears: b1=b2 = years c1=c2 = (64/38) b2 d1=d2 = (48/24) c2 e1=e2=e3=e4 = (127/32) d2 f1=f2 = (188/53) e4 g1=g2 = (30/54) f2 (saros x4 scale) h1=h2 = (20/60) g2 i1 = (15/60) h2 (exeligmos dial) The number of teeth in gears l1, ma1, mb1, mb2 isn't shown and there are more gears that are known but are not linked to any other known gears, so there must be additional unknown gears (a lot of which are the subject of the paper). There is also the known "pin-and-slot epicyclic lunar mechanism" which implements the first anomaly of the moon without affecting its rotational period. Nevertheless we can at least start to answer the question by looking at the known ratios above. The most complex fraction (highest value of numerator*denominator) is h1=h2 = 238760/27189 years: that gear turns 238760 times each 27189 years. The other denominators are all factors of 27189, so the overall cycle for those known gears is 27189 years. The answer to your question (period of the entire device) would have to be a multiple of 27189.
[...] Also, if the antikythera device really is a "planetarium in a box", and if it really does do a good job of modeling the known universe at the time, how come we can't tell _the exact date_ of its demise ? [...] This is essentially equivalent to being able to determine the exact time of an earthquake from the position of the hands of clocks which stopped as a result of the earthquake.
The pointers (marking the positions on the scales and dials) were lost, so we don't know what moon position, date, year, etc. was displayed on it when the ship sank. In other words, the hands of the clocks came off the dials because the earthquake was really strong. Maybe I don't understand your question. -- Robert Munafo -- mrob.com Follow me at: gplus.to/mrob - fb.com/mrob27 - twitter.com/mrob_27 - mrob27.wordpress.com - youtube.com/user/mrob143 - rilybot.blogspot.com