[aprssig] Re: metrics
KA8VIT ka8vit at ka8vit.comSat Sep 8 14:29:17 UTC 2007
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Interesting. Steve Dimse wrote: > > On Sep 8, 2007, at 3:58 AM, Mark Fellhauer wrote: > >> A circle has 360 degrees because a year is 13 Lunar periods of 28 days. > > The moonth (not a misspelling, that is the origin of month) is 29.53 > days when viewed from the earth, and 27.322 days when viewed from a > fixed point in space. The difference is the earth moves along its > orbit, so the moon has to rotate further for us to see the same phase. > Note that NEITHER is 28 days. Using the actual lunar rotation time of > 27.322, 13 periods is just over 355 days. Twelve earth-apparent moon > rotations gets you to a nearby value a bit over 354 days. The moon has > rotated thirteen times, the earth going once around its orbit makes > the moon do the extra turn not visible from our vantage point. Humans, > in their usual self-centered manner, choose to define a moonth on > their perception, rather than the moon's perspective. > > The truth behind 360 is, again, more fascinating to me than the myth. > The Babylonians began a number of long-lived non-decimal systems, > which included the number of minutes in an hour, hours in a day, and > degrees in a circle. The reason was they never developed fractional > arithmetic. Instead, to make their life easier they used "magic > numbers", numbers which were evenly divisible by as many factors as > possible. > > 24 is evenly divisible by 1, 2, 3, 4, 6, 8, 12, and 24. > > 60 is evenly divisible by 1, 2, 3, 4, 5, 6, 10, 12, 20, 30, and 60. > > 360 is left as an exercise for the reader, suffice it to say it is 60 > * 6, so it has all the factors of 60 and then some. > > Some scholars believe the Babylonians chose 360 as the magic number to > use because it was close to the number of days in a year, which is > independent of the lunar cycle. Others believe it was chosen because > it was closest to their ability to sub-divide a circle. I've never > read a source that equated it to the lunar cycle, but we do not know > for sure, and if you want to say they rounded up from TWELVE lunar > cycles I have no basis to argue. But it is indisputably the > Babylonians and not the Greeks that broke the circle into 360 degrees, > and the reason for that number was their inability to do any > fractional math. And if you want to equate it to the lunar cycle, it > has to be twelve, because they did not know the earth orbited the sun. > > Sorry for prolonging the off-topic thread, but I really hate it when > people perpetuate erroneous information. Repeat after me, bad data is > worse than no data at all! > > Steve K4HG > > _______________________________________________ > aprssig mailing list > aprssig at lists.tapr.org > https://lists.tapr.org/cgi-bin/mailman/listinfo/aprssig > > -- Bill Chaikin, KA8VIT USS COD Amateur Radio Club - W8COD WW2 Submarine USS COD SS-224 (NECO) ka8vit at ka8vit.com http://ka8vit.com http://www.usscod.org QRP-L#: 2596 FP#: 1043 SKCC#: 2593
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