rotation period

In astronomy, the rotation period or spin period of a celestial object has two definitions. The first one corresponds to the sidereal rotation period, i.e., the time that the object takes to complete a full rotation around its axis relative to the background stars. The other type of commonly used "rotation period" is the object's synodic rotation period, which may differ, by a fraction of a rotation or more than one rotation, to accommodate the portion of the object's orbital period around a star or another body during one day.