Neptune is the eighth planet from the Sun. Neptune was the first planet located through mathematical predictions. Nearly 4.5 billion km from the Sun, Neptune orbits the Sun once every 165 years. It is invisible to the naked eye because of its extreme distance from Earth. Interestingly, due to Pluto's unusual elliptical orbit, Neptune is actually the farthest planet (including dwarf planets) from the Sun for a 20-year period out of every 248 Earth years.