The period of rotation of a Solar System object is the length of time it takes that object to spin once around on its axis. For example the Earth takes 24 hours to spin once around its axis. Its period of rotation is 24 hours or a day.
First, let's consider how to find the period of rotation of an object, be it a planet, orange, or basketball.
One way is to find a landmark or surface feature, and to measure the time it takes for an object to spin around and come back to the same spot. (Unfortunately, not all planets have a mark "stamped" on them. You'll have to find something to use as a landmark or surface feature later on.)
Before you start exploring with real planets, let's practice with something more simple, such as basketball.
Examples:
1. If a planet turns halfway (180 degrees) in 12 hours, how long will it take to go all the way around (360 degrees)?
Solution:
Known turn = 180 degrees
Full turn = 360 degrees
Known time = 12 hours
Full rotation time = ?
360 degrees / 180 degrees = Full rotation time / 12 hours
Full time rotation = 360 degrees/180 degrees x 12 hours = 24 hours
2. Often you can't see the planet during its entire rotation. (The Sun comes up in the morning and obscures our view of the planets; the planet slips behind clouds or below the horizon; etc.) Let's consider the following example.
We know that a surface feature of a rotating object covers 20 degrees in 4 hours. What is the period of its rotation? (To solve this problem, you will need to use some ratios.)
Solution:
Known turn = 20 degrees
Full turn = 360 degrees
Known time = 4 hours
Full rotation time = ?
20 degrees / 360 degrees = 4 hours / Full rotation time
Full time rotation = (360 degrees) (4 hours) / 20 degrees = 72 hours
Looks like you now understand what the period of rotation is, and are ready to work with rotation rates (or angular velocities, as they are sometimes called.)