Until the 1840s, astronomers believed that there were seven planets in our solar system. When astronomers began to study the orbit of Uranus more closely, they discovered irregularities that could not be explained. Various scientists assumed that the irregularities of Uranus' orbit were caused by gravitational_forces originating from an eighth planet further away from the Sun. Independently of each other, the Englishman Adams and the Frenchman Leverrier correctly calculated the position of this planet.
It was finally detected at this location by the astronomers of the Berlin Observatory in 1846. Due to its blue color, the planet was named after the Roman god of the seas. The distinct blue appearance of Neptune actually results from the methane clouds in its atmosphere.
Neptune is the fourth and also the smallest of the "gas giant" planets. Its diameter is approximately 49,500 kilometers and its mass is 17 times the mass of the Earth. A day on Neptune is only 16 hours long. One Neptune year, i.e. the time it takes the planet to complete a revolution around the Sun, corresponds to 165 Earth years.
The mean distance from the Sun is more than 4.5 billion kilometers. The Voyager space probe, which flew past Neptune in 1989, has brought a wealth of information on this planet. It detected for example that Neptune has a ring system. It consists of three rings, where the outer ring shows prominent protruding arcs. Temperatures are generally very low at around minus 200┬░ Celsius.
Similar to Jupiter and Saturn, Neptune emits more energy than it receives from the Sun. Scientists believe that this is due to the cooling of the planet's core, which is continuing. The equivalent to the Great Red Spot on Jupiter is the Great Dark Spot on Neptune. It is believed to be the eye of an enormous storm.
