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In astronomy, the rotation period or spin period [1] of a celestial object (e.g., star, planet, moon, asteroid) has two definitions. The first one corresponds to the sidereal rotation period (or sidereal day ), i.e., the time that the object takes to complete a full rotation around its axis relative to the background stars ( inertial space ).
A synodic day (or synodic rotation period or solar day) is the period for a celestial object to rotate once in relation to the star it is orbiting, and is the basis of solar time. The synodic day is distinguished from the sidereal day , which is one complete rotation in relation to distant stars [ 1 ] and is the basis of sidereal time.
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At the equator, the solar rotation period is 24.47 days. This is called the sidereal rotation period, and should not be confused with the synodic rotation period of 26.24 days, which is the time for a fixed feature on the Sun to rotate to the same apparent position as viewed from Earth (the Earth's orbital rotation is in the same direction as the Sun's rotation).
The slightly longer stellar period is measured as the Earth rotation angle (ERA), formerly the stellar angle. [4] An increase of 360° in the ERA is a full rotation of the Earth. A sidereal day on Earth is approximately 86164.0905 seconds (23 h 56 min 4.0905 s or 23.9344696 h).
Most bodies have a period between 2 and 20 hours. [1] [a] This is a list of fast rotators—"minor planets" (which includes asteroids) that have an exceptionally short rotation period, i.e. high rotation rate or spin rate. In some cases the rotation period is not constant because the object tumbles (see List of tumblers).
Most bodies have a period between 2 and 20 hours. [1] [a] This is a list of slow rotators—minor planets that have an exceptionally long rotation period. This period, typically given in hours, and sometimes called rotation rate or spin rate, is a fundamental standard physical property for minor planets.
Pluto's rotation period, its day, is equal to 6.387 Earth days. [ 3 ] [ 101 ] Like Uranus and 2 Pallas , Pluto rotates on its "side" in its orbital plane, with an axial tilt of 120°, and so its seasonal variation is extreme; at its solstices , one-fourth of its surface is in continuous daylight, whereas another fourth is in continuous darkness ...