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Neptune is the eighth and farthest known planet from the Sun. It is the fourth-largest planet in the Solar System by diameter, ... Its sidereal rotation period (day) ...
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).
At the time of his first observation in December 1612, it was stationary in the sky because it had just turned retrograde that very day; because it was only beginning its yearly retrograde cycle, Neptune's motion was thought to be too slight, and its apparent size too small, to clearly appear to be a planet in Galileo's small telescope. [10]
All but the outer two are within Neptune-synchronous orbit (Neptune's rotational period is 0.6713 day or 16 hours [20]) and thus are being tidally decelerated. Naiad, the closest regular moon, is also the second smallest among the inner moons (following the discovery of Hippocamp), whereas Proteus is the largest regular moon and the second ...
In 2010, Helled and collaborators suggested that the rotation periods of both Uranus and Neptune are in fact unknown. They suggested that the length of day on the ice giants are ~16.58 hr (Uranus) and 17.46 (Neptune). In 2015, Helled and collaborators accurately calculated Saturn's rotation time (10 hours, 32 minutes, 45 seconds). [7]
The last time Neptune's rings were seen in detail was during a flyby in 1989 by NASA's Voyager 2 spacecraft as it journeyed beyond the solar system and into interstellar space. That historic flyby ...
NASA's Juno spacecraft captured this view of Jupiter during the mission's 54th close flyby of the giant planet Sept. 7, 2023.
Triton orbits Neptune in a retrograde orbit—revolving in the opposite direction to the parent planet's rotation—the only large moon in the Solar System to do so. [ 3 ] [ 13 ] Triton is thought to have once been a dwarf planet from the Kuiper belt , captured into Neptune's orbit by the latter's gravity .