Rotation period (astronomy)

 ( Kinematic Properties ) 

In astronomy, the rotation period or spin period 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). The other type of commonly used "rotation period" is the object's synodic rotation period (or solar day), 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.

---

Measuring rotation For solid objects, such as rocky planets and asteroids, the rotation period is a single value. For gaseous or fluid bodies, such as and , the period of rotation varies from the object's equator to its pole due to a phenomenon called differential rotation. Typically, the stated rotation period for a giant planet (such as Jupiter, Saturn, Uranus, Neptune) is its internal rotation period, as determined from the rotation of the planet's magnetic field. For objects that are not sphere symmetry, the rotation period is, in general, not fixed, even in the absence of gravity or tidal force forces. This is because, although the rotation axis is fixed in space (by the conservation of angular momentum), it is not necessarily fixed in the body of the object itself. As a result of this, the moment of inertia of the object around the rotation axis can vary, and hence the rate of rotation can vary (because the product of the moment of inertia and the rate of rotation is equal to the angular momentum, which is fixed). For example, Hyperion, a moon of Saturn, exhibits this behaviour, and its rotation period is described as Chaos theory.

---

Rotation period of selected objects

~28 days (equatorial) Kenneth J. H. Phillips (1995). 9780521397889, Cambridge University Press. ISBN 9780521397889
none (due to spin-orbit locking)
~15.786 days	~15d 18h 53m|| ~15.7872 days |

---

See also

• Apparent retrograde motion
• Day length fluctuations
• Earth's rotation periods
• List of slow rotators (minor planets)
• List of fast rotators (minor planets)
• Retrograde motion
• Rotation (astronomy)
• Rotational speed
• Stellar rotation
• Synodic day

---

Notes

---

External links

• (1999). 9780521572958, Cambridge University Press. . ISBN 9780521572958
  Note, the rotation periods for Mercury and Earth in this work may be inaccurate.

Post Comment