||A small, glassy material formed by the impact of a large body, usually a meteor or asteroid. Tektites are commonly found at the sites of meteor craters.
||An instrument that uses lenses and sometimes mirrors to collect large amounts of light from distant objects and enable direct observation and photography. A Telescope can also include any instrument designed to observe distant objects by their emissions of invisible radiation such as x-rays or radio waves.
||The sunset or sunrise line on the Moon or a planet.
||A term used to describe anything originating on the planet Earth.
||A name given to a planet composed mainly of rock and iron, similar to that of Earth.
||The differential gravitational pull exerted on any extended body within the gravitational field of another body.
||Frictional heating of a satellite's interior due to flexure caused by the gravitational pull of its parent planet and/or other neighboring satellites.
||The passage of a celestial body across an observer's meridian; also the passage of a celestial body across the disk of a larger one.
||Any one of a number of celestial objects that orbit the Sun at a distance beyond the orbit of the planet Neptune.
||An object orbiting in the Lagrange points of another (larger) object. This name derives from a generalization of the names of some of the largest asteroids in Jupiter's Lagrange points. Saturn's moons Helene, Calypso and Telesto are also sometimes called Trojans.