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Neptune's internal structure resembles that of Uranus. Its atmosphere forms about 5 to 10% of its mass and extends perhaps 10 to 20% of the way towards the core. Pressure in the atmosphere reaches about 10 GPa, or about 10 5 atmospheres. Increasing concentrations of methane, ammonia and water are found in the lower regions of the atmosphere. [30]
Though all stars and planets appear to move from east to west on a nightly basis in response to the rotation of Earth, the outer planets generally drift slowly eastward relative to the stars. Asteroids and Kuiper Belt objects (including Pluto ) exhibit apparent retrograde motion.
That is, they all have prograde rotation relative to the Sun except those of Uranus. If there is a collision, material could be ejected in any direction and coalesce into either prograde or retrograde moons, which may be the case for the moons of dwarf planet Haumea, although Haumea's rotation direction is not known. [15]
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 .
The South Pole is the other point where Earth's axis of rotation intersects its surface, in Antarctica. Earth rotates once in about 24 hours with respect to the Sun, but once every 23 hours, 56 minutes and 4 seconds with respect to other distant stars . Earth's rotation is slowing slightly with time; thus, a day was shorter in the past.
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).
Direction determination refers to the ways in which a cardinal direction or compass point can be determined in navigation and wayfinding.The most direct method is using a compass (magnetic compass or gyrocompass), but indirect methods exist, based on the Sun path (unaided or by using a watch or sundial), the stars, and satellite navigation.
Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times the mass of Earth and slightly larger than Neptune. [a] Neptune orbits the Sun once every 164.8 years at an average distance of 30.1 astronomical units (4.50 × 10 9 km).