Neptune

Neptune , historically also

Neptune in true color[a] 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[1]
Discovered by	Johann Galle Urbain Le Verrier John Couch Adams
Discovery date	23 September 1846
Designations
Pronunciation	US: /ˈnɛptuːn/ (listen), UK: /-tjuːn/[2]
Named after	Latin Neptunus, via French Neptune
Adjectives	Neptunian (/nɛpˈtjuːniən/),[3] Poseidean[4]
Orbital characteristics[9][b]
Epoch J2000
Aphelion	30.33 AU (4.54 billion km)
Perihelion	29.81 AU (4.46 billion km)
Semi-major axis	30.07 AU (4.50 billion km)
Eccentricity	0.008678
Orbital period	164.8 yr 60,195 days 89,666 Neptunian solar days[5]
Synodic period	367.49 days[6]
Average orbital speed	5.43 km/s[6]
Mean anomaly	259.883°
Inclination	1.770° to ecliptic 6.43° to Sun's equator 0.74° to invariable plane[7]
Longitude of ascending node	131.783°
Time of periastron	2042-Sep-04[8]
Argument of perihelion	273.187°
Known satellites	16
Physical characteristics
Mean radius	24,622±19 km[10][c]
Equatorial radius	24,764±15 km[10][c] 3.883 Earths
Polar radius	24,341±30 km[10][c] 3.829 Earths
Flattening	0.0171±0.0013
Surface area	7.6187×109 km2[11][c] 14.98 Earths
Volume	6.253×1013 km3[6][c] 57.74 Earths
Mass	1.02413×1026 kg[6] 17.147 Earths 5.15×10−5 Suns
Mean density	1.638 g/cm3[6][d]
Surface gravity	11.15 m/s2[6][c] 1.14 g
Moment of inertia factor	0.23[12] (estimate)
Escape velocity	23.5 km/s[6][c]
Rotation period	0.67125 d 16 h 6 m 36 s[5]
Sidereal rotation period	0.6713 day[6] 16 h 6 min 36 s
Equatorial rotation velocity	2.68 km/s (9,650 km/h)
Axial tilt	28.32° (to orbit)[6]
North pole right ascension	19h 57m 20s[10] 299.3°
North pole declination	42.950°[10]
Albedo	0.290 (bond)[13] 0.442 (geom.)[14]
Surface temp. min mean max 1 bar level 72 K (−201 °C)[6] 0.1 bar (10 kPa) 55 K (−218 °C)[6]
Apparent magnitude	7.67[15] to 8.00[15]
Absolute magnitude (H)	−6.9[16]
Angular diameter	2.2–2.4″[6][17]
Atmosphere[6]
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.

Neptune's atmosphere is mostly hydrogen and helium. It also contains small amounts of methane which makes the planet appear blue.^[18][19][20] Neptune's blue color is similar, but slightly darker, than the color of Uranus. Neptune also has the strongest winds of any planet in the Solar System, as high as 2,100 km/h or 1,300 mph.

Urbain Le Verrier and John Couch Adams were the astronomers who discovered Neptune. Neptune was not discovered using a telescope. It was the first planet to be discovered using mathematics. In 1821, astronomers saw that Uranus' orbit was different from what they expected. Another nearby planet's mass was changing Uranus' orbit. They found Neptune was the cause.

Voyager 2 visited Neptune on 25 August 1989. It was the only spacecraft to visit the planet. Neptune used to have a huge storm known as the "Great Dark Spot". Voyager 2 discovered the spot in 1989. The dark spot was not seen in 1994, but new spots were found since then. It is not known why the dark spot disappeared. Visits by other space probes have been planned.

Neptune has five rings surrounding it. However, the rings are hard to see from Earth.
Cite error: There are <ref group=lower-alpha> tags or {{efn}} templates on this page, but the references will not show without a {{reflist|group=lower-alpha}} template or {{notelist}} template (see the help page).

1. ↑ Hamilton, Calvin J. (4 August 2001). "Neptune". Views of the Solar System. Archived from the original on 15 July 2007. Retrieved 13 August 2007.
2. ↑ Walter, Elizabeth (21 April 2003). Cambridge Advanced Learner's Dictionary (2nd ed.). Cambridge University Press. ISBN 978-0-521-53106-1.
3. ↑ "Neptunian". Oxford English Dictionary. Oxford University Press. 2nd ed. 1989.
4. ↑ "Enabling Exploration with Small Radioisotope Power Systems" (PDF). NASA. September 2004. Archived from the original (PDF) on 22 December 2016. Retrieved 26 January 2016.
5. ↑ ^{5.0 5.1} Seligman, Courtney. "Rotation Period and Day Length". Archived from the original on 28 July 2011. Retrieved 13 August 2009.
6. ↑ ^{6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 6.11 6.12} Williams, David R. (1 September 2004). "Neptune Fact Sheet". NASA. Archived from the original on 1 July 2010. Retrieved 14 August 2007.
7. ↑ Souami, D.; Souchay, J. (July 2012). "The solar system's invariable plane". Astronomy & Astrophysics. 543: 11. Bibcode:2012A&A...543A.133S. doi:10.1051/0004-6361/201219011. A133.
8. ↑ "HORIZONS Planet-center Batch call for September 2042 Perihelion". ssd.jpl.nasa.gov (Perihelion for Neptune's planet-center (899) occurs on 2042-Sep-04 at 29.80647406au during a rdot flip from negative to positive). NASA/JPL. Archived from the original on 7 September 2021. Retrieved 2021-09-07.
9. ↑ Yeomans, Donald K. "HORIZONS Web-Interface for Neptune Barycenter (Major Body=8)". JPL Horizons On-Line Ephemeris System. Archived from the original on 7 September 2021. Retrieved 18 July 2014.—Select "Ephemeris Type: Orbital Elements", "Time Span: 2000-01-01 12:00 to 2000-01-02". ("Target Body: Neptune Barycenter" and "Center: Solar System Barycenter (@0)".)
10. ↑ ^{10.0 10.1 10.2 10.3 10.4} Cite error: The named reference Seidelmann Archinal A'hearn et al. 2007 was used but no text was provided for refs named (see the help page).
11. ↑ Cite error: The named reference fact2 was used but no text was provided for refs named (see the help page).
12. ↑ de Pater, Imke; Lissauer, Jack J. (2015). Planetary Sciences (2nd updated ed.). New York: Cambridge University Press. p. 250. ISBN 978-0-521-85371-2. Archived from the original on 26 November 2016. Retrieved 17 August 2016.
13. ↑ Cite error: The named reference Pearl_et_al_Neptune was used but no text was provided for refs named (see the help page).
14. ↑ Cite error: The named reference Mallama_et_al was used but no text was provided for refs named (see the help page).
15. ↑ ^{15.0 15.1} Cite error: The named reference Mallama_and_Hilton was used but no text was provided for refs named (see the help page).
16. ↑ "Encyclopedia - the brightest bodies". IMCCE. Archived from the original on 24 July 2023. Retrieved 2023-05-29.
17. ↑ Espenak, Fred (20 July 2005). "Twelve Year Planetary Ephemeris: 1995–2006". NASA. Archived from the original on 5 December 2012. Retrieved 1 March 2008.
18. ↑ info@noirlab.edu. "Gemini North Telescope helps explain why Uranus and Neptune are different colors - observations from Gemini Observatory, a program of NSF's NOIRLab, and other telescopes reveal that excess haze on Uranus makes it paler than Neptune". www.noirlab.edu. Retrieved 2022-07-30.
19. ↑ Laboratory, By NSF’s NOIRLab (National Optical-Infrared Astronomy Research. "Why Uranus and Neptune Are Different Colors". NASA Solar System Exploration. Retrieved 2023-03-06.
20. ↑ Magazine, Smithsonian; Kuta, Sarah. "Why Neptune Appears Bluer Than Its Cousin Uranus". Smithsonian Magazine. Retrieved 2022-07-30.