The ancient Babylonians knew that the Earth revolves around the sun and that it takes about 360 days to make one complete revolution. Of course, we know that the required time is much closer to 365•1/4 days. In any case, one logical explanation for the choice of a base of 60 suggest that it resulted from their 360 day calendar. From this developed the idea that a circle consisted of 360°. This meant that the earth's movement along its orbit about the sun was of 1/360 of 360° or 1° each day. This notion could then have been coupled with their knowledge that the circumference of a circle can be divided into six equal arcs by marking it off, as shown below, so long as the compass setting is equal to the radius of the circle. Then, if radii are drawn from the center of the circle to each of the six points marked on the circumference, the resulting central angles each measure 60%. Thus, we see that a unit of sixty might well have been chosen as the base of the Babylonian numeration. system just as 60° was a kind of unit for circle measurement. The importance of 60 as a base appears again when the Babylonians established a 24-hour. day. Each hour was divided into 60 minutes, and each minute was further divided into 60 seconds. This system is the one still used by us in modern times.