Rotation period

Animated rotation of asteroid 433 Eros

In astronomy, the rotation period of a celestial object is the time that it takes to complete one revolution around its axis of rotation relative to the background stars. It differs from the planet's solar day, which includes an extra fractional rotation needed to accommodate the portion of the planet's orbital period during one day.

Measuring rotation

For solid objects, such as rocky planets and asteroids, the rotation period is a single value. For gaseous/fluid bodies, such as stars and gas giants, the period of rotation varies from the equator to the poles due to a phenomenon called differential rotation. Typically, the stated rotation period for a gas giant (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 spherically symmetrical, the rotation period is, in general, not fixed, even in the absence of gravitational or tidal 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.[citation needed] 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). Hyperion, a satellite of Saturn, exhibits this behaviour, and its rotation period is described as chaotic.

Other Languages
العربية: فترة التناوب
azərbaycanca: Fırlanma periodu
беларуская: Перыяд вярчэння
Esperanto: Rotacia periodo
فارسی: دوره چرخش
한국어: 자전 주기
हिन्दी: घूर्णन काल
hrvatski: Period rotacije
Bahasa Indonesia: Periode rotasi
Lëtzebuergesch: Rotatiounsperiod
македонски: Вртежен период
Bahasa Melayu: Tempoh putaran
Nederlands: Rotatieperiode
日本語: 自転周期
norsk nynorsk: Rotasjonsperiode
polski: Okres obrotu
Simple English: Rotation period
slovenčina: Rotačná perióda
slovenščina: Vrtilna doba
српски / srpski: Период ротације
srpskohrvatski / српскохрватски: Period rotacije
українська: Період обертання
中文: 自轉週期