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[aprssig] Re: metrics

KA8VIT ka8vit at ka8vit.com
Sat Sep 8 14:29:17 UTC 2007


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
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Bill Chaikin, KA8VIT
USS COD Amateur Radio Club - W8COD
WW2 Submarine USS COD SS-224 (NECO)

ka8vit at ka8vit.com

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