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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 ).
Six of the planets also rotate about their axis in this same direction. The exceptions – the planets with retrograde rotation – are Venus and Uranus. Venus's axial tilt is 177°, which means it is rotating almost exactly in the opposite direction to its orbit. Uranus has an axial tilt of 97.77°, so its axis of rotation is approximately ...
The pronunciation of the name Uranus preferred among astronomers is / ˈ jʊər ə n ə s / YOOR-ə-nəs, [1] with the long "u" of English and stress on the first syllable as in Latin Uranus, in contrast to / j ʊ ˈ r eɪ n ə s / yoo-RAY-nəs, with stress on the second syllable and a long a, though both are considered acceptable. [g]
Alone but certainly unique, Uranus rotates at a nearly 90-degree angle and is surrounded by 13 icy rings. Images of which were captured in rich detail last year by the James Webb Space Telescope .
The length of a day on Uranus as measured by Voyager 2 is 17 hours, 14 minutes. [49] Uranus was shown to have a magnetic field that was misaligned with its rotational axis, unlike other planets that had been visited to that point, [50] [53] and a helix-shaped magnetic tail stretching 10 million kilometers (6 million miles) away from the Sun. [50]
But long before that, Voyager 2 stopped by Uranus, coming within 50,600 miles of Uranus' cloudtops. While encountering the planet on Jan. 24, 1986, ...
Illustrations depict how Uranus' magnetosphere, or protective bubble, was behaving before Voyager 2's arrival (left) and during the spacecraft's flyby (right).
Many exoplanets (especially the close-in ones) are expected to be in spin–orbit resonances higher than 1:1. A Mercury-like terrestrial planet can, for example, become captured in a 3:2, 2:1, or 5:2 spin–orbit resonance, with the probability of each being dependent on the orbital eccentricity. [15]