This property has many useful applications, such as dividing the world into 24 time zones, each of which is nominally 15° of longitude, to correlate with the established 24-hour day convention.įinally, it may be the case that more than one of these factors has come into play. Furthermore, it is divisible by every number from 1 to 10 except 7. Īnother motivation for choosing the number 360 may have been that it is readily divisible: 360 has 24 divisors, making it one of only 7 numbers such that no number less than twice as much has more divisors (sequence A072938 in the OEIS). Eratosthenes used a simpler sexagesimal system dividing a circle into 60 parts. Timocharis, Aristarchus, Aristillus, Archimedes, and Hipparchus were the first Greeks known to divide the circle in 360 degrees of 60 arc minutes. One sixtieth of this, using their standard sexagesimal divisions, was a degree.Īristarchus of Samos and Hipparchus seem to have been among the first Greek scientists to exploit Babylonian astronomical knowledge and techniques systematically. A chord of length equal to the radius made a natural base quantity. The earliest trigonometry, used by the Babylonian astronomers and their Greek successors, was based on chords of a circle. Īnother theory is that the Babylonians subdivided the circle using the angle of an equilateral triangle as the basic unit, and further subdivided the latter into 60 parts following their sexagesimal numeric system. The use of a calendar with 360 days may be related to the use of sexagesimal numbers. Some ancient calendars, such as the Persian calendar and the Babylonian calendar, used 360 days for a year. Ancient astronomers noticed that the sun, which follows through the ecliptic path over the course of the year, seems to advance in its path by approximately one degree each day. One theory states that it is related to the fact that 360 is approximately the number of days in a year. The original motivation for choosing the degree as a unit of rotations and angles is unknown. History A circle with an equilateral chord (red). Because a full rotation equals 2 π radians, one degree is equivalent to π / 180 radians. It is not an SI unit-the SI unit of angular measure is the radian-but it is mentioned in the SI brochure as an accepted unit. One degree (shown in red) and eighty nine degrees (shown in blue)Ī degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by ° (the degree symbol), is a measurement of a plane angle in which one full rotation is 360 degrees.
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