Neptune is so far away it is hard to see the planet in much detail. It appears as a dim bluish-green world through telescopes. It is located 30 Astronomical Units from the Sun. Neptune is nearly the same size as Uranus with a diameter of 30,760 miles (49,500 km) and is sometimes thought of as Uranus' twin. A Neptunian day is only 17 hours and 50 minutes long. Astronomers have calculated that it takes 164.8 Earth years to complete one revolution around the Sun.
Hydrogen and helium dominate Neptune's makeup as it does the other gas-giants. It is also made of methane, water, and other compounds. Methane gives it its blue color as it does to Uranus. Scientists believe Neptune's internal structure is also very much like Uranus.
When Voyager 2 flew by Neptune in 1989, it spotted rings like those encircling Saturn and Uranus. Neptune's rings seem to be made up mostly of dust-sized particles. Neptune is a very stormy planet with gale-force winds that have been measured at speeds up to 700 miles per hour. It has two dark storm spots. The larger is names the "Great Dark Spot" and is as big as the planet Earth. Neptune has faint rings and 13 moons, one of which is named Triton. Triton is nearly as big as Earth and is thought to be the coldest place in the Solar System.
We often think of Neptune as the eighth planet from the Sun followed by the planet Pluto. However, this is not always accurate. Pluto has a very strange elliptical orbit around the Sun. This odd orbit is responsible for bringing Pluto inside Neptune's orbit and closer to the Sun for 20 out of every 248 years. This will not happen again until the year 2247.