Neptune is an icy ball of gas located 30 Astronomical Units from the sun. Neptune is the outermost planet in the Solar System as Pluto (and other similar bodies further out than Neptune) are now called Dwarf Planets. Neptune is nearly as large as 60 Earths. It orbits the sun in 165 years and turns once on its axis in 16 hours. Neptune has 8 known moons and Voyager 2 discovered 6 of them. Neptune also has rings like Jupiter and Saturn and Uranus.  
It appears that the outer part of Neptune consists of helium, hydrogen, methane and water while the interior has molten rock and liquid ammonia. Further Neptune is a very windy place. Winds of 2,000 kilometers (1,200 miles) an hour have been measured.
It once had a big dark spot on it, like Jupiter's big red spot, but that went away.
Neptune was discovered in the middle of the 19th Century after a mathematician named Le Verrier analysed irregularities in the orbits of Uranus and predicted that there was another planet influencing Uranus. We aren’t sure if Le Verrier was clever or lucky.    
- The Rings of Neptune
- Rings of Neptune
- Neptune Facts
- That means when Neptune was last in the same position relative to the sun where it is now Astronomers knew the sun is a star and part of a vast system of stars. The distances to some of the stars had been measured showing they were very bright and very far away, (Who discovered that the Sun was a star?) also the spectra of light from other stars had been compared to the spectrum of sunlight and astronomers knew they were similar. (Fraunhofer Lines) Astronomers didn't yet know that the Milky Way is one Galaxy among many.
- Reappraising Leverrier's discovery of Neptune
- The Planet Neptune
- Enchanted learning about Neptune
- The Nine Planets - Neptune Video teaching about Neptune