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 Click here to return to the Astronomy Archives

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