Adams and Leverrier predicted the existence of the planet Neptune back in 1845. Neptune is very difficult to observe from the earth because of the distance, and the earth's atmosphere. The closest and best look that we have had at Neptune was provided by the Voyager 2 flyby in 1989.
Neptune is the most distant planet from the sun. It was once believed that Pluto was a planet Pluto beyond Neptune, but astronomers have declared that Pluto is not a planet but one of many dwarf planets in our solar system.
Neptune has a diameter that is about four times larger than earths. Computer models suggest that Neptune has a rocky core that comprises about 15 earth masses at the center, but there is no confirmation of this theory. Neptune has a rotation period of about 16 hours. Neptune has an internal heat source, and it produces about 2.7 times more heat than it absorbs.
Strong winds, bright, high-altitude clouds, and two large dark spots attributed to long-lived giant storm systems were reveled by the 1989 Voyager flyby. Wind speeds are as high as 739 miles per hour. The larger of the two dark spots that Voyager reveals is called the "Great Dark Spot."
Neptune's rings were first detected from Earth in 1983, but no real study could be conducted at that time. It wasn't until the data supplied by the Voyager 2 flyby was available that any determination about the rings could be disseminated. There are two bright rings and two fainter rings. The rings rotate in the same direction as Neptune, and they are all close to the equator.
Triton and Nereid are the two large moons of Neptune and are visible from Earth. Voyager 2 discovered six more moons, and one of them is actually larger than Nereid; but it is difficult to see because it orbits so close to Neptune.
