Neptune , historically also

Neptune in true color as captured by Voyager 2. Like Uranus, Neptune has a muted appearance; several storms can still be seen, such as the Great Dark Spot at the center.
Discovery
Discovered by	Johann Galle Urbain Le Verrier John Couch Adams
Discovery date	23 September 1846
Designations
Pronunciation	US: /ˈnɛpuːn/ ( listen), UK: /-tjuːn/
Named after	Latin Neptunus, via French Neptune
Adjectives	Neptunian (/nɛpˈtjuːniən/), Poseidean
Orbital characteristics
Epoch J2000
Aphelion	Lua error in Module:Convert at line 272: attempt to index local 'cat' (a nil value).
Perihelion	Lua error in Module:Convert at line 272: attempt to index local 'cat' (a nil value).
Semi-major axis	Lua error in Module:Convert at line 272: attempt to index local 'cat' (a nil value).
Eccentricity	0.008678
Orbital period	164.8 yr 60,195 days 89,666 Neptunian solar days
Synodic period	367.49 days
Average orbital speed	5.43 km/s
Mean anomaly	259.883°
Inclination	1.770° to ecliptic 6.43° to Sun's equator 0.74° to invariable plane
Longitude of ascending node	131.783°
Time of periastron	2042-Sep-04
Argument of perihelion	273.187°
Known satellites	16
Physical characteristics
Mean radius	24,622±19 km
Equatorial radius	24,764±15 km 3.883 Earths
Polar radius	24,341±30 km 3.829 Earths
Flattening	0.0171±0.0013
Surface area	7.6187×109 km2 14.98 Earths
Volume	6.253×1013 km3 57.74 Earths
Mass	1.02413×1026 kg 17.147 Earths 5.15×10−5 Suns
Mean density	1.638 g/cm3
Surface gravity	11.15 m/s2 1.14 g
Moment of inertia factor	0.23 (estimate)
Escape velocity	23.5 km/s
Rotation period	0.67125 d 16 h 6 m 36 s
Sidereal rotation period	0.6713 day 16 h 6 min 36 s
Equatorial rotation velocity	2.68 km/s (9,650 km/h)
Axial tilt	28.32° (to orbit)
North pole right ascension	19h 57m 20s 299.3°
North pole declination	42.950°
Albedo	0.290 (bond) 0.442 (geom.)
Surface temp. min mean max 1 bar level 72 K (−201 °C) 0.1 bar (10 kPa) 55 K (−218 °C)
Apparent magnitude	7.67 to 8.00
Absolute magnitude (H)	−6.9
Angular diameter	2.2–2.4″
Atmosphere
Scale height	19.7±0.6 km
Composition by volume	80%±3.2% hydrogen 19%±3.2% helium 1.5%±0.5% methane ~0.019% hydrogen deuteride ~0.00015% ethane Icy volatiles: ammonia water ice ammonium hydrosulfide methane ice (?)

Neptune is the eighth and farthest planet from the Sun in the Solar System. It is an ice giant. It is the fourth-largest planet in the system.

Neptune's mass is 17 times Earth's mass and a little bit more than Uranus' mass. Neptune is denser and smaller than Uranus. Because of its greater mass, Neptune's gravity makes its atmosphere smaller and denser.

It was named after the Roman god of the sea, Neptune. Neptune's astronomical symbol is ♆, the trident of the god Neptune.