G - H - I

Select the letter that (probably) leads off the word in question. Please suggest new words or corrections.

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G

• GRB: Abbr. See "gamma ray burst".

• galaxy: A system of billions of stars, gas and dust that has coalesced to form a huge body. Ex. The Milky Way galaxy.

• gamma ray burst: An intense, concentrated burst of gamma radiation whose origin is not yet understood.

• Ganymede: A large rocky moon orbiting Jupiter that was discovered in 1610 by Galileo.

• globular cluster: Gravitationally bound concentrations of approximately ten thousand to one million stars, spread over a volume of several tens to about 200 light years in diameter. Also see "star cluster" and "open cluster". Ex. M13 - the Great Hercules Globular Cluster.

• gravity: The attracting force that exists between two or more objects. Every object with mass has gravity, even though its effects can be minimal and undetectable.

• Greenwich Mean Time: See "Universal Coordinated Time"

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H

• helium: An inert, monoatomic, gaseous element occurring in the atmosphere of the sun and stars, and in small quantities in the earth's atmosphere. Helium is by-product of the thermonuclear fusion of hydrogen occuring in the Sun.

• hydrogen: A colorless, highly flammable gaseous element, the lightest of all gases and the most abundant element in the universe. The thermonuclear fusion of hydrogen to helium in the Sun produces its heat and energy.

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I

• Io: One of Jupiter's four large moons discovered by Galileo in 1610. Io is one of the only known sources of active volcanism in the solar system.

• ion: A condition in which an atom has acquired a net electric charge by gaining or losing one or more electrons.

• ionization: The formation of ions by heat, electrical discharge, radiation, etc.

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