The question
Why 360, and not 100 or 1,000?
The short answer
The 360-degree circle comes from Babylonian astronomy. The sun moves roughly one degree a day, and 360 divides evenly in an unusually large number of ways.
What science knows
Historical FactBabylonian astronomers divided the zodiac into 12 signs of 30 degrees, and Greek astronomers such as Hipparchus and Ptolemy used 360 degrees, subdivided in base 60, for their tables.
The pattern
Established Mathematics360 = 2³ × 3² × 5 has 24 divisors, including every number from 1 to 10 except 7. A circle of 360 degrees splits cleanly into halves, thirds, quarters, fifths, sixths, eighths, ninths, tenths and twelfths.
What is still uncertain
Mixed EvidenceHistorians debate how much the choice came from the year’s roughly 360 days, and how much from base-60 arithmetic. Both likely played a part.
Why humans find it interesting
Historical FactOther systems exist. Revolutionary France introduced the grade, 400 to a circle, to fit the metric system. Mathematicians prefer radians, 2π to a circle, because they make calculus simpler.
CUE perspective
CUE PerspectiveEvery astrological aspect CUE and others use, the 60° sextile or the 120° trine, is a division of this Babylonian circle.
The circle is a human choice that stuck because it works, which is a good way to think about many systems CUE draws on.