### Why 360?

Monday, October 5, 2009
Why do you think that people use the number 360 as the number for a full circle? It wasn't just picked at random. There are many reasons that people may have picked 360.

One of them is that the ancient Babylonians used a sexagesimal number system. Sexagesimal means having a base of sixty. Well, the Babylonians used the number 60 as their base number, whereas we use the number 10. They realized that the earth took approximately 360 days to rotate (one year). The astronomers of the time noticed that the celestial pole (imaginary axis line) seemed to advance in a circle by 1-360th every day (one degree). That is one reason why we use 360 as our circle number.

Another reason that 360 may have been used is that the number 360 has 24 divisors, including every number from 1 to 10 except 7 and 12, 15, 18, 20, 24, 30, 36, 40, 45, 60, 72, 90, 120, 180, and 360. If the degrees in a circle were to be divisible by every number from 1-10, there would be 2520 degrees in a circle, which is a much more complicated number than 360, and it would get really confusing to divide 2520 by 7 or something like that.

Thanks for reading my post! I hope that it helped at least someone to understand why we use 360 as our full circle number.