Neptune is the fourth planet in terms of size and the eighth in terms of distance to the Sun. The average distance from Neptune to the Sun is 4.5 billion kilometers and its average linear diameter is approximately 49.400 km, that is, about 3.8 times that of Earth. The rotation period is about 16 hours and the sidereal period of revolution is 164.79 years.
The surface temperature of Neptune is about -218 ° C, similar to that of Uranus, which is more than 1,500 km closer to the sun, therefore, scientists assume that Neptune must have some internal source of heat. The atmosphere is mainly composed of hydrogen and helium, but the presence of more than 3% methane gives the planet its surprising blue color.
Eight satellites are known that revolve around Neptune, two of which can be observed from Earth. The largest and brightest is Triton, discovered in 1846, the year in which Neptune was observed for the first time. Triton, with a diameter of 2,705 km is little smaller than the Earth's moon. Nereo, the second satellite, has a diameter of only 320 km. The Voyager 2 planetary probe discovered another six satellites in 1989.
Neptune is also surrounded by five rings. Its magnetic field is inclined more than 50 ° with respect to the axis of rotation.
The discovery of Neptune was one of the successes of mathematical astronomy. In 1846, to explain the alterations in the orbit of Uranus, the French astronomer Urbain Le Verrier calculated the existence and position of a new planet. The same year, German astronomer Johann Gottfried Galle discovered the planet.
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