On September 23, 1846, the planet Neptune was discovered by Johann Galle, a German astronomer at the Berlin Obervatory. Galle discovered the planet, not by directly observing it, but through mathematical calculations based on variations in gravity on its neighboring planet, Uranus. Italian astronomer Galileo observed Neptune as early as 1612, but he thought it was a star.
Neptune, the 8th planet from the Sun, is named after the Roman god of the sea, because of its blue color. It is 4 times bigger than Earth. Neptune rotates on its axis faster then Earth does; a day on Neptune is 16 hours long, whereas a day on Earth is 24 hours long. Neptune takes longer to orbit the sun than Earth does, though, so a year on Neptune is the same as 165 Earth years. Neptune has eight known moons, while Earth only has one.
Neptune is a gas giant, meaning that it is made up mostly of gases, as opposed to rock and other solid matter. Neptune is made up mostly of hydrogen, helium, ammonia and methane.
