Encyclopedia of Astrobiology

2015 Edition
| Editors: Muriel Gargaud, William M. Irvine, Ricardo Amils, Henderson James (Jim) CleavesII, Daniele L. Pinti, José Cernicharo Quintanilla, Daniel Rouan, Tilman Spohn, Stéphane Tirard, Michel Viso

Rotational Velocity

  • Daniel Rouan
Reference work entry
DOI: https://doi.org/10.1007/978-3-662-44185-5_1390

Synonyms

Definition

The rotational velocity is the rate at which a celestial body (star, planet, galaxy) rotates on itself, generally around one of its axes of symmetry. The rotational velocity is the number of revolutions per time unit. Units are cycles s−1 or Hz.

The rotational velocity of a body is a result of the  angular momentumthat is possessed by the matter from which it condensed (e.g., molecular cloud, debris disk, pre-galactic halo). This quantity being conserved during any process of collapse or condensation, the object spins faster, as its size is reduced. A typical rotational velocity of a star like the Sun is one rotation per month; however, young stars can spin at a rate 40 times faster, and in the extreme case of millisecond pulsars, this rate can reach 716 rotations per second. For planets, except for those in our solar system, rotations are not generally known. Jupiter makes one rotation in about 10 h, while one rotation takes 240 days on Venus....

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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  1. 1.LESIA, Observatoire Paris-Site de MeudonMeudonFrance