免费日韩片_欧美成人精品一区二区男人小说_国产乱码一区二区三区四区_国产精品国产三级国产aⅴ入口_成人看的污污超级黄网站免费_欧美一级在线免费观看_成人午夜免费无码福利片_国产乱人伦偷精品视频色欲_aaa少妇高潮大片免费看_国产精品1234_亚洲精品国产suv一区88_中文字字幕在线中文无码_精品亚洲区_午夜九九九_国产av国片精品jk制服丝袜_色综合亚洲_亚洲成av人片无码bt种子下载_欧美色就色_精品少妇的一区二区三区四区_男人用嘴添女人下身免费视频

學代數的時候老師說一圈是360度，就這樣記在腦子里了。可是，一圈為什么不能是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（預兆）. 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.

（來源：www.wonderquest.com 英語點津Helen編輯）