Neptune is the farthest planet from our Sun. Neptune is the only planet that is so far away that you can’t see it without a telescope. Neptune (NEPP-toon) is an icy planet, about the same size as Uranus. Neptune’s probably a lot like Uranus in other ways, too. Neptune has a rocky core about the size of the Earth, made of rock and ice. Around that, there’s a thick atmosphere made out of hydrogen, helium and methane.
Neptune looks blue partly because the methane in the atmosphere absorbs red light and reflects blue light. It’s definitely not oceans. Neptune also has rings around it, and at least thirteen moons.
Because Neptune’s so far from the Sun, it’s very cold there – about -400 degrees Celsius. Neptune has so far to go that it takes Neptune almost 165 of our years to go around the Sun.
Because you can’t see Neptune without a telescope, nobody knew about Neptune until 1846. That’s when Urbain Le Verrier used Newton’s Laws and a lot of math to predict that there had to be a planet right there, because the gravity of that planet was pulling on other objects. So astronomers in Berlin started to look where he had said there should be a planet, and then they found it. Everyone was excited, because that showed that Newton’s laws really worked. They named the planet Neptune – the Roman name for the god Poseidon – because it was blue. But the Greeks and Romans never knew anything about the planet Neptune.