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T

Tektite
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.

Telescope
An instrument used to collect large amounts of light from far away objects and increase their visibility to the naked eye. Telescopes can also enlarge objects that are relatively close to the Earth.

Terminator
The boundary between the light side and the dark side of a planet or other body.

Terrestrial
A term used to describe anything originating on the planet Earth.

Terrestrial Planet
A name given to a planet composed mainly of rock and iron, similar to that of Earth.

Tidal Force
The differential gravitational pull exerted on any extended body within the gravitational field of another body.

Tidal Heating
Frictional heating of a satellite's interior due to flexure caused by the gravitational pull of its parent planet and/or other neighbouring satellites.

Transit
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.

Trojan
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.

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