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'''Neptune''' is the eighth and farthest [[planet]] from the [[sun]]. Long after its discovery, which was determined using mathematics, [[astronomy|astronomers]] had no notion of how remarkable Neptune would prove to be until [[Voyager 2]] flew by Neptune in 1989.

'''Neptune''' is the eighth and farthest [[planet]] from the [[sun]]. It was discovered in 1846 by German astronomer [[Johann Gotfried Galle]] based on orbital calculations by French mathematician [[Urbain Le Verrier]].

 

The U.S. spacecraft [[Voyager 2]] flew by Neptune in 1989. The planet is named after the Roman god of the sea. It is 17 times the mass of the Earth and is composed of 80 percent hydrogen and 19 percent helium.

== Discovery ==

== Discovery ==

In 1613, [[Galileo Galilei]] first observed what he took to be a [[star]] close to [[Jupiter]]. On the next two nights this "star" had moved with respect to another true star. Then the object fell from his field of view, and bad weather prevented Galileo from observing it again. He would never know the magnitude of his oversight.<ref name=Arnett>Arnett, Bill. "[http://www.nineplanets.org/Neptune.html Neptune]." ''[http://www.nineplanets.org/ The <s>Nine</s> 8 Planets],'' September 2, 2004. Accessed May 6, 2008.</ref>

In 1613, [[Galileo Galilei]] first observed what he took to be a [[star]] close to [[Jupiter]]. On the next two nights this "star" had moved with respect to another true star. Then the object fell from his field of view, and bad weather prevented Galileo from observing it again. He would never know the magnitude of his oversight.<ref name=Arnett>Arnett, Bill. "[http://www.nineplanets.org/Neptune.html Neptune]." ''[http://www.nineplanets.org/ The <s>Nine</s> 8 Planets],'' September 2, 2004. Accessed May 6, 2008.</ref>

In 1781, [[William Herschel]] discovered Neptune's twin [[Uranus]]. But astronomers noticed that that planet's orbit deviated from the strict [[Isaac Newton|Newtonian]] model. [[John Couch Adams]] and [[Urbain Le Verrier]] independently predicted another planet beyond Uranus to account for these irregular motions. Though Adams never published his predictions, Le Verrier did. [[Johann Gottfried Galle]] and his student [[Heinrich L. d'Arrest]] used those predictions to help him search the sky, and he found the eighth planet within one degree of where Le Verrier's numbers predicted it to be.<ref name=Smith>Smith, Bradford A. "[http://www.worldbookonline.com/wb/Article?id=ar386900 Neptune]." ''World Book Online Reference Center,'' [[National Aeronautics and Space Administration|NASA]], 2004. Accessed May 6, 2008.</ref>

In 1781, [[William Herschel]] discovered Neptune's twin [[Uranus]]. But astronomers noticed that that planet's orbit deviated from the strict [[Isaac Newton|Newtonian]] model. [[John Couch Adams]] and Le Verrier independently predicted another planet beyond Uranus to account for these irregular motions. Though Adams never published his predictions, Le Verrier did. Galle and his student [[Heinrich L. d'Arrest]] used those predictions to help him search the sky, and he found the eighth planet within one degree of where Le Verrier's numbers predicted it to be.<ref name=Smith>Smith, Bradford A. "[http://www.worldbookonline.com/wb/Article?id=ar386900 Neptune]." ''World Book Online Reference Center,'' [[National Aeronautics and Space Administration|NASA]], 2004. Accessed May 6, 2008.</ref>

A protracted dispute between the [[United Kingdom|British]] and [[France|French]] arose as to the naming rights and the proposed name of the planet.<ref name=Arnett/> Galle at one point proposed naming the planet after Le Verrier. Eventually, however, the community of astronomers chose the name Neptune, for the Roman god of the sea and brother of Jupiter. They also chose as a symbol for Neptune the trident, the three-pronged sceptre that the mythical Neptune carried.

A protracted dispute between the [[United Kingdom|British]] and [[France|French]] arose as to the naming rights and the proposed name of the planet.<ref name=Arnett/> Galle at one point proposed naming the planet after Le Verrier. Eventually, however, the community of astronomers chose the name Neptune, for the Roman god of the sea and brother of Jupiter. They also chose as a symbol for Neptune the trident, the three-pronged sceptre that the mythical Neptune carried.