Neptune was discovered because of its gravitational effects on the orbit of Uranus. Soon after the discovery of Uranus, the planet consistently failed to follow the predicted (calculated) path. This let astronomers to believe that there must be another planet. By observing Uranus, astronomers could calculate the orbit and approximate mass of the other planet. On September 23, 1846, Neptune was observed by J. Galle near the predicted spot. This makes Neptune the first planet to be discovered by means of calculations.

Neptune is the most distant Jovian planet. This cold world does however give off 2.8 times as much energy as it receives from the sun. This means that Neptune has internal heat.

When Voyager 2 visited Neptune in August 1989, a lot of new discoveries were made about this planet. Six new moons (total of 8 moons) were discovered and previously unknown features of the planet were revealed. Neptune turned out to be a beautifull briliant blue planet. It also has a dark spot, similar to the red spot on Jupiter, and cloud formations in the upper atmosphere. The Great Dark Spot is a circular storm the size of the Earth. The storm spins counter-clockwise and moves in a westward direction at almost 1200 Km/hour. Wind speeds of up to 2400 Km/hour were detected. This is the highest for any planet in the solar system.