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The average distance between Neptune and the Sun is 4.5 billion km (about 30.1 astronomical units (AU), the mean distance from the Earth to the Sun), and it completes an orbit on average every 164.79 years, subject to a variability of around ±0.1 years. The perihelion distance is 29.81 AU, and the aphelion distance is 30.33 AU.
The apsides refer to the farthest (2) and nearest (3) points reached by an orbiting planetary body (2 and 3) with respect to a primary, or host, body (1). An apsis (from Ancient Greek ἁψίς (hapsís) 'arch, vault'; pl. apsides / ˈ æ p s ɪ ˌ d iː z / AP-sih-deez) [1] [2] is the farthest or nearest point in the orbit of a planetary body about its primary body.
[9] [10] On the other hand, the time-averaged distance (rather than the inverse of the average inverse distance) between the centers of Earth and the Moon is 385,000.6 km (239,228.3 mi). One can also model the orbit as an ellipse that is constantly changing, and in this case one can find a formula for the semi-major axis, again involving ...
It treats Earth as stationary globe around which Sun orbits, and makes no mention of Uranus, Neptune and Pluto. [11] It calculates the Earth's diameter to be 8,000 miles (modern: 7,928 miles), [ 6 ] the diameter of the Moon as 2,400 miles (actual ~2,160) [ 6 ] and the distance between the Moon and the Earth to be 258,000 miles [ 6 ] (now known ...
Proteus is the second-largest moon of Neptune and is the largest of its regular prograde moons. It is about 420 km (260 mi) in diameter, larger than Nereid, Neptune's third-largest moon. It was not discovered by Earth-based telescopes because Proteus orbits so close to Neptune that it is lost in the glare of reflected sunlight. [15]
Triton's orbit precesses forward relative to Neptune's rotation with a period of about 678 Earth years (4.1 Neptunian years), [4] [5] making its Neptune-orbit-relative inclination vary between 127° and 173°. That inclination is currently 130°; Triton's orbit is now near its maximum departure from coplanarity with Neptune's.
It orbits Neptune at a distance of between 25.7 and 67.7 million km (for comparison, the Sun-Mercury distance varies between 46 million and 69.8 million km) and requires almost 25 Earth years to make one orbit. The orbit of this satellite is close to the theoretical stable separation from Neptune for a body in a retrograde orbit.
In order of distance from Neptune, the regular moons are Naiad, Thalassa, Despina, Galatea, Larissa, Hippocamp, and Proteus. 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 ...