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Origin of 360 Degrees and 365 Days
Name: Daniel
Status: other
Grade: other
Location: NV
Country: N/A
Date: 1/25/2006
Question:
If the earth takes 365 days to complete a cycle and
fulfill a circle/year, why are there only 360 degrees in a circle?
Also if the earth rotates counter-clockwise, how does the sun rise
in the east? I am having trouble visualizing this.
I would really appreciate your insight!
Replies:
Daniel,
It is coincidence that there are 360 degrees in a circle and 365 1/4
days a year.
In the Old Babylonian period, there was a unit of time corresponding
to the "barleycorn." In Sumerian, one barleycorn (called se) was
1/180 of a shekel. In late Babylonian astronomical texts, it was 1/6
of a finger. Since 1 finger was 1/12 or a degree, we have 1 degree =
72 barleycorns and 15 degrees = 1080 barleycorns. So why are we
worried about 15 degrees? That is the amount of arc length the sun
travels in the sky in one hour, where one hour is 1/24 of a day. It
was convenient to divide the day into 12 daylight and 12 night time
parts. At 15 degrees per hour, and 24 hours per day, this would give
360 degrees of rotation per day. From this, it is an easy jump to
360 degrees in a circle.
If you look into Biblical texts,you will find that hours were broken
up into 1080 parts (we now divide our hours into 3600 seconds)
corresponding to these barleycorns. The relationship of 1 finger = 6
barleycorns is well known in Arabic, Syriac, and Sanskrit astronomy.
Some scholars claim that 1080 (and 360) were used because these
numbers are easily divisible by so many numbers (notably 7
excepted). There does not seem to be great evidence for this.
An expert on the History of Mathematics, which involves some of the
ancient astronomy was Professor Otto Neugebauer of Brown
University. I am guessing his work in this area was done in the mid 1900's.
As for counterclockwise rotation of Earth, this is only if your frame
of reference is looking down from the North Pole. Indeed, this would
necessitate the sun rising in the east. Spin a basketball
counterclockwise as you look down on the axis of rotation. Have a
light illuminating it from only one side. East is the direction a
point moves from the ball's shadow into light.
---Nathan A. Unterman
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Update: June 2012
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