知识百科：为什么一圈是360度
学代数的时候老师说一圈是360度，就这样记在脑子里了。可是，一圈为什么不能是100度或者280度呢?We delve back to arrive at a probable answer. A line of ancient peoples
(Sumerians, Akkadians, and Babylonians) who lived in Mesopotamia (now southern
Iraq) invented writing, observed the skies, and invented a 360-degree circle to
describe their findings. About 3000 BC, the Sumerians invented writing. They
also had a calendar, dating from 2400 BC, that divided the year into 12 months
of 30 days each, that is, 360 days.
The Sumerians watched the Sun, Moon, and the five visible planets (Mercury,
Venus, Mars, Jupiter, and Saturn), primarily for omens(预兆). They did not try to
understand the motions physically. They did, however, notice the circular track
of the Sun's annual path across the sky and knew that it took about 360 days to
complete one year's circuit. Consequently, they divided the circular path into
360 degrees to track each day's passage of the Sun's whole journey. This
probably happened about 2400 BC.
That's how we got a 360 degree circle. Around 1500 BC, Egyptians divided
the day into 24 hours, though the hours varied with the seasons originally.
Greek astronomers made the hours equal. About 300 to 100 BC, the Babylonians
subdivided the hour into base-60 fractions: 60 minutes in an hour and 60 seconds
in a minute. The base 60 of their number system lives on in our time and angle
divisions.
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