Rotation period (astronomy)

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File:EpicEarth-Globespin-tilt-23.4.gif

Earth's rotation imaged by Deep Space Climate Observatory, with axis tilt

In astronomy, the rotation period or spin period<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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 rotationEdit

For solid objects, such as rocky planets and asteroids, the rotation period is a single value. For gaseous or fluid bodies, such as stars and giant planets, 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 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.Template: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). For example, Hyperion, a moon of Saturn, exhibits this behaviour, and its rotation period is described as chaotic.

Rotation period of selected objectsEdit

File:Planets and dwarf planets' tilt and rotation speed.webm

Animation of the planets and dwarf planets (Pluto and Ceres) relative rotation period (using sidereal time)

Celestial objects	Rotation period with respect to distant stars, the sidereal rotation period (compared to Earth's mean Solar days)		Synodic rotation period (mean Solar day)	Apparent rotational period viewed from Earth
Sun Template:Efn-lr	25.379995 days (Carrington rotation) 35 days (high latitude)	25^d 9^h 7^m 11.6^s 35^d		~28 days (equatorial)<ref name="Phillips1995-78">Template:Cite book</ref>
Mercury	58.6462 days<ref name=Allen296>Template:Cite book</ref>	58^d 15^h 30^m 30^s	citation	CitationClass=web }}</ref>\|\|
Venus	−243.0226 daysTemplate:Efn-lr<ref>Template:Cite journal</ref>	−243^d 0^h 33^m	citation	CitationClass=web }}</ref>\|\|
Earth	0.99726968 days<ref name=Allen296/>Template:Efn-lr	0^d 23^h 56^m 4.0910^s	1.00 days (24^h 00^m 00^s)
Moon	27.321661 days<ref name=Allen>Template:Cite book</ref> (equal to sidereal orbital period due to spin-orbit locking, a sidereal lunar month)	27^d 7^h 43^m 11.5^s	29.530588 days<ref name=Allen/> (equal to synodic orbital period, due to spin-orbit locking, a synodic lunar month)	none (due to spin-orbit locking)
Mars	1.02595675 days<ref name=Allen296/>	1^d 0^h 37^m 22.663^s	citation	CitationClass=web }}</ref> days\|\|
Ceres	0.37809 days<ref name="Chamberlain2007">Template:Cite journal</ref>	0^d 9^h 4^m 27.0^s	0.37818 days
Jupiter	0.41354 days(average) 0.4135344 days (deep interiorTemplate:Efn-lr) 0.41007 days (equatorial) 0.4136994 days (high latitude)	0^d 9^h 55^m 30^s<ref name=Allen296/> 0^d 9^h 55^m 29.37^s<ref name=Allen296/> 0^d 9^h 50^m 30^s<ref name=Allen296/> 0^d 9^h 55^m 43.63^s<ref name=Allen296/>	Template:Val (9 h 55 m 33 s)<ref name="planet_years">{{#invoke:citation/CS1\|citation	CitationClass=web }}</ref> (average) \|\|
Saturn	Template:Val days (average, deep interiorTemplate:Efn-lr) 0.44401 days (deep interiorTemplate:Efn-lr) 0.4264 days (equatorial) 0.44335 days (high latitude)	Template:RA Template:+- <ref name="NASA-20190118">Template:Cite news</ref><ref name="APJ-20190117">Template:Cite journal</ref> 0^d 10^h 39^m 22.4^s<ref>Template:Cite journal</ref> 0^d 10^h 13^m 59^s<ref name="system">Template:Cite book</ref> 0^d 10^h 38^m 25.4^s<ref name="system"/>	Template:Val (10 h 32 m 36 s)<ref name="planet_years"/>
Uranus	−0.71833 days<ref name=Allen296/>Template:Efn-lr	−0^d 17^h 14^m 24^s	Template:Val (−17 h 14 m 23 s)<ref name="planet_years"/>
Neptune	0.67125 days<ref name=Allen296/>	0^d 16^h 6^m 36^s	Template:Val (16 h 6 m 36 s)<ref name="planet_years"/>
Pluto	−6.38718 days<ref name=Allen296/>Template:Efn-lr (synchronous with Charon)	–6^d 9^h 17^m 32^s	Template:Val (–6^d 9^h 17^m 0^s)<ref name="planet_years"/>
Haumea	0.1631458 ±0.0000042 days<ref name="hour">Template:Cite journal</ref>	0^d 3^h 56^m 43.80 ±0.36^s	0.1631461 ±0.0000042 days
Makemake	0.9511083 ±0.0000042 days<ref name="Hromakina2019">Template:Cite journal</ref>	22^h 49^m 35.76 ±0.36^s	0.9511164 ±0.0000042 days
Eris	~15.786 days<ref name="Szakats2022">Template:Cite journal</ref>	~15^d 18^h 53^m	~15.7872 days

NotesEdit

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ReferencesEdit

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External linksEdit

Template:Cite bookNote, the rotation periods for Mercury and Earth in this work may be inaccurate.

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