Due to its elliptical orbit, Neptune's distance from the Sun fluctuates between 2.77 and 2.82 billion miles. The eighth planet in the solar system, Neptune is also the furthest from the Sun.
While first observed by Galileo Galilei in 1612, Neptune was not officially recognized as a planet until 1846. Neptune's extreme distance from the Sun means that it takes over 164 years for it to complete a single orbit. The Voyager 2 probe was the only spacecraft to have visited Neptune, and in 1989 it was able to provide the first detailed pictures of the solar system's most distant planet.