Neptune is the eighth planet from the Sun. Named after the Roman god of the Sea, it is the fourth largest planet by diameter
and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than it's near twin Uranus.
It's astronomical symbol is a stylized version of the fod Neptune's trident.
Discoverd on September 23, 1845, Neptune was the first planet found by mathematical prediction
rather than by empirical observation. Unexpected changes in the orbit of Uranus led astronomers to deduce that its orbit was
subject of gravitational perturbation by an unknown planet. Neptune was subsequently found within a degree of its predicted
position, and its largest moon, Triton, was discovered shortly after, even though none of the remaining 12 moons of Neptune
were located untill the 20th century. Neptune has been visited by only one spacecraft, the Voyger 2, which flwer by the planet
on August 25, 1989.
Neptune is similar in compisition to Uranus, and both have composotions which differ from Jupiter
and Saturn. Neptunes atmosphere is compsed mostly of hydrogen abd helium, along with traces of other stuff. Astronomers sometimes
catergorize Neptune (and Uranus) as "ice giants". The interior of Neptune it primarily composed of ice and rock. Traces
if methane in the outermost regions in part account for this planet's blue appearence.
