Answer: epicycles

AnswerCrossword Clue
EPICYCLESInner circles, in astronomy models
EPICYCLESCircles rolling around other circles
epicyclesEPICYCLE, a small circle that moves in the circumference of another
epicyclesA small circle whose center moves around the circumference of a larger one
epicyclesA circle of this type used to describe planetary orbits in the Ptolemaic system