Gravity: a force that pulls objects towards each other. Objects with greater mass exert a stronger gravitational pull on objects with less mass. In addition, the closer two objects are, the stronger the force of gravity between them is.

Orbit: the path an object follows as it travels around another object. Earth orbits the sun; the moon orbits Earth.

Solar system: the sun and all the objects in space that orbit it, including the planets and their moons, as well as asteroids, comets, Kuiper belt objects and meteoroids.

Telescope: a tool used to observe or study distant objects by gathering and focusing the electromagnetic radiation that comes from them. Most telescopes gather visible light, while others use other forms of radiation such as radio waves or X-rays.