The planet Neptune was discovered in September 23, 1846, the first half of the 19th century. As of today, July 12th, 2011, it has made 1 full orbit of the Sun since its discovery.
Neptune is our solar system’s furthest known planet (with Pluto now being considered a dwarf planet). Its orbit is so far out that it requires 164.79 years to complete a year. Today marks the day that would make it a complete years since its discovery by Johann Galle.
Uranus, whose wobbly orbit was used to locate Neptune, has by comparison completed 2 years since its discovery in1781. It is also well into completing a third year.