The 360-degree circle is 4400 years old
Q: Why does a circle have 360 degrees; why not 100 degrees? Also why is a degree 60 minutes and
a minute 60 seconds? --HSR, Pakistan
A: 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.
[Corel] Ancient Babylonians may have invented the sundial
The Sumerians watched the Sun, Moon, and the five visible planets (Mercury, Venus, Mars, Jupiter, and Saturn), primarily for omens.
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.
An 100-degree circle makes sense for base 10 people like ourselves. But the base-60 Babylonians came up with 360 degrees and we cling
to their ways-4,400 years later.
(Answered Jun. 21, 2002)
Calendars through the ages: Babylonian
Why files: Writing origin
U of Louisville: Babylonian magic and religion
U of Texas: Babylonian history, astronomy, math
Otto Neugebauer, The Exact Sciences in Antiquity
Riverdeep: time keeping