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How to Calculate the Period of Rotation

The period of rotation is the length of time it takes for an astronomical body to complete a full revolution, in other words, to complete one full rotation about its axis. As an example, the Earth's period of rotation of approximately 24 hours, which is the reason that a day on Earth is 24 hours long. Calculating the period of rotation for different bodies requires a small understanding of geometry, but is a relatively straightforward process.

Instructions

- 1
  Determine how much the body has rotated in a given period of time. For example, assume that a planet or other spherical astronomical body has rotated 120 degrees in 15 hours.
- 2
  Divide the number of degrees in a complete circle (360 degrees) by the number of degrees the planet has rotated. In the example above, dividing 360 degrees by 120 degrees gives 3. Call this result A.
- 3
  Multiply result A by the time it took the planet to rotate the measured amount. Concluding the example, multiplying 3 by 15 hours gives 45 hours. This is the period of rotation of the planetary body.

Astronomy