Asteroid – A small body of rock that orbits the sun. Most of them are located in the main asteroid belt which is between the orbits of Mars and Jupiter. Atmosphere – The layer of gas around a planet Comet – A comet is a large body of dust and ice that orbit the Sun. Best known for their long, streaming tails. Day – The length of time it takes the Earth to spin on its axis – 24 hours. Dwarf planet – A Object that is round and orbits the sun, just like planets do. A dwarf planet is much smaller than a planet. Galaxy – A huge collection of gas, dust, and billions of stars and their solar systems, all held together by gravity. Gravity – The force by which a planet or other body draws objects toward its center. The force that attracts a moon to a planet, or a planet to a star. Milky Way – A galaxy consisting of several hundred billion of stars one of which is the sun. This is the galaxy where we live in. Moon – A moon is a smaller object orbiting a planet. Some planets have many moons. Ea rth has just one. Orbit – A regular repeating path that one object in space takes around another one. Planet – A large body of either rock or gas that follows a consistent orbit around a star. Solar System – A set that includes a star and all of the matter that orbits it, including planets, moons, asteroids, comets, and other objects. Space – The void that exist between the objects in the universe. Star – A star is a huge ball of very hot gases, that gives off lots of light and heat. Some stars have planets orbiting around them, but not all do. Sun – The star in the center of our Solar System. Universe – The Universe is everything that exists: all the galaxies, all the stars, all the planets and everything in between. Year – The length of time it takes the E arth to travel around the Sun - 365 days. Words to Know