Why 360 Degrees in a Circle?
Have you ever thought about how a circle has 360 degrees? The Earth takes one year to orbit the Sun. And a year is just a little more than 365 days. That means that the Earth rotates on its axis a little more than 365 times every year. And it means that every day the Sun appears to move about 1/365 of the way along a huge circle projected onto the sky that extends all the way around the Earth, called the ecliptic.
We humans like to divide a circle up into 360 pie-shaped wedges. Each of these wedges contains an angle at its vertex, and we say that the size of this angle is 1 degree. As you also probably know, degrees aren’t the only way we can measure angles. Angles are also measured in radians and sometimes, very rarely, they are even measured in obscure military units called gradians, which is why a lot of calculators have “deg rad grad” buttons on them). While we don’t know exactly why the 360 degree convention was chosen (more on that in a minute), we do know approximately when and where it all started. At least we know that it came to be a long, long time ago—as in 4 or 5 thousand years ago with the Babylonians, the Greeks, and perhaps other even more ancient groups.
If you lived a few millennia ago and didn’t have modern instruments to accurately record the positions of objects in the sky, you might conclude that the Sun moves about 1/360 of the way along this circle every day, which is exactly what ancient astronomers did. And they then made a leap and decided to divide this circle on the sky—and all circles—into 360 even parts so that the Sun would move through 1 part per day. Each of these parts was dubbed 1 degree, thus giving us the idea that a circle contains 360 degrees.
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.
In 1936, a tablet was excavated some 200 miles from Babylon. Here one should make the interjection that the Sumerians were first to make one of man's greatest inventions, namely, writing; through written communication, knowledge could be passed from one person to others, and from one generation to the next and future ones. They impressed their cuneiform, wedge-shaped script on soft clay tablets with a stylus, and the tablets were then hardened in the sun. The mentioned tablet, whose translation was partially published only in 1950, is devoted to various geometrical figures, and states that the ratio of the perimeter of a regular hexagon to the circumference of the circumscribed circle equals a number which in modern notation is given by 5760+366025760+36602 , the Babylonians used the sexagesimal system, i.e., their base was 60 rather than 10. The Babylonians knew, of course, that the perimeter of a hexagon is exactly equal to six times the radius of the circumscribed circle, in fact that was evidently the reason why they chose to divide the circle into 360 degrees (and we are still burdened with that figure to this day). The tablet, therefore, gives ... π=258=3.125π=258=3.125. That's how we got a 360-degree circle.
The ancient Babylonian and Persian calendars were both based upon 360-day years, it seems likely that this simple astronomical observation is the reason a circle contains 360 degrees.
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. A 100-degree circle makes sense for base 10 people like us. But the base-60 Babylonians came up with 360 degrees and we cling to their ways – 4,400 years later.
If you lived a few millennia ago and didn’t have modern instruments to accurately record the positions of objects in the sky, you might conclude that the Sun moves about 1/360 of the way along this circle every day, which is exactly what ancient astronomers did. And they then made a leap and decided to divide this circle on the sky—and all circles—into 360 even parts so that the Sun would move through 1 part per day. Each of these parts was dubbed 1 degree, thus giving us the idea that a circle contains 360 degrees.
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.
In 1936, a tablet was excavated some 200 miles from Babylon. Here one should make the interjection that the Sumerians were first to make one of man's greatest inventions, namely, writing; through written communication, knowledge could be passed from one person to others, and from one generation to the next and future ones. They impressed their cuneiform, wedge-shaped script on soft clay tablets with a stylus, and the tablets were then hardened in the sun. The mentioned tablet, whose translation was partially published only in 1950, is devoted to various geometrical figures, and states that the ratio of the perimeter of a regular hexagon to the circumference of the circumscribed circle equals a number which in modern notation is given by 5760+366025760+36602 , the Babylonians used the sexagesimal system, i.e., their base was 60 rather than 10. The Babylonians knew, of course, that the perimeter of a hexagon is exactly equal to six times the radius of the circumscribed circle, in fact that was evidently the reason why they chose to divide the circle into 360 degrees (and we are still burdened with that figure to this day). The tablet, therefore, gives ... π=258=3.125π=258=3.125. That's how we got a 360-degree circle.
The ancient Babylonian and Persian calendars were both based upon 360-day years, it seems likely that this simple astronomical observation is the reason a circle contains 360 degrees.
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. A 100-degree circle makes sense for base 10 people like us. But the base-60 Babylonians came up with 360 degrees and we cling to their ways – 4,400 years later.
