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Everyone knows there are 360 degrees in a circle. Why? A circle could have a 1,000° which would make a half circle equal 500° and a quarter circle 250°. Who chose the number 360? Was there a vote? Who do we blame? Inquiring minds want to know!

Two circles getting in each other's way

2017 Total Solar Eclipse from Canyon City, OR

As it turns out there are at least two reasons we use 360° as the number to define a complete circle. One reason has to do with astronomy and the other with mathematics.

360 Degrees? Blame the Babylonians

The Greeks are partly responsible for defining the numerical value for a circle, but really it was the Babylonians. It may even be farther back than the Babylonians, but someone erased their hard drive and now we will never know.

Apparently, the Babylonians loved the number ’60.’ They created a number system using Base 60 (we use Base 10.) The number 60 is amazing because it can be divided into so many factors. 60 can be divided evenly by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, and 60. Since the Babylonians loved 60, the fact that a circle can be divided into six equilateral triangles made 360 the best option for defining the numerical value of a circle.

We don’t actually know if it was the Babylonians, but we do know that several prominent Greek mathematicians used 360° as the numerical value for a circle. It is written…in Greek of course.

Star Gazers In a 360 Days

But long before the Babylonians, it was obvious to anyone who looked up at the sky at night that the stars followed a circular pattern through the year. If one noted the position of a star or constellation on a particular night and time, next year that star would be in the same place on the same day and time.

The elapsed number of nights for a full circle? About 360. Anyone who tracked the stars would have noted that the circular pattern of the stars resumed after about 360 days.

The reason we have 360° is most likely because of the speed at which the Earth rotates, (once every 24 hours,) and there are approximately 360 rotations (days) in a year.

Metric Circles?

Believe it or not, there were attempts to make circles metric. It didn’t take. There are some uses for it, but the 360° value is more accepted ‘around’ (that’s a joke) the world.