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Some Astronomy Definitions

asteroid: A sizeable, rocky body smaller than a planet that orbits the Sun (less sizeable objects are called meteoroids)

binary star: Two stars that orbit each other

comet: A body of ices and rock that orbits the Sun and has a tail generated when the Sun and the solar wind heat, release and blow gases and dust off the comet

constellation: A collection of stars that make up an imaginary image

dark nebula: A non-luminous nebula that blocks out light from the stars behind it thereby creating a dark sky patch

galaxy: a collection of several million to several trillion stars that are gravitationally bound to one another

galaxy cluster: a collection of a dozen to several thousand galaxies that are gravitationally attracted to each other

globular cluster: An approximately spherically shaped star cluster of ten-thousand to a million stars

elliptical galaxy: An ellipsoidally shaped galaxy

emission nebula: A nebula that is hot enough to emit light

irregular galaxy: An irregularly shaped galaxy

lenticular galaxy: A pancake shaped galaxy with no spiral arms

lunar eclipse: When the Earth passes between the Sun and the Moon and blocks out all (full) or some (partial) of the sunlight being reflected off the Moon thereby rendering it dark

magnitude: The apparent brightness of a star or object in the night sky; each increase by one in magnitude corresponds to 2.5 times fainter

meteor: A dust particle or rock that burns up in Earth's atmosphere thereby creating a streak of light; also known as a shooting star

Milky Way: Our galaxy, the galaxy of which the Sun is a member

moon: A non-luminous body that orbits a planet

nebula: A large cloud of gas and dust that appears as a fuzzy object in a telescope

open cluster: An irregularly shaped star cluster of a dozen to a few thousand stars

planet: A sizeable non-luminous body that orbits a star

planetary nebula: A nebula surrounding a star that was created earlier when the outer portion of the star blew off

reflection nebula: A nebula whose dust is illuminated by light from one or more nearby stars

solar eclipse: When the Moon passes in front of the Sun and blocks out all (full) or some (partial) of its light thereby rendering the Sun black

solar system: The Sun and any other bodies that are gravitationally bound to it such as the planets, their moons, asteroids and comets

spiral galaxy: A galaxy that is pancake shaped with several spiral arms

star: A luminous ball of gas of hydrogen, helium and other elements that generates its energy through nuclear fusion in its core

star cluster: A collection of a dozen to a million stars that are relatively close to one another

supernova: A star that explodes and becomes very bright

supernova remnant: A nebula created by the explosion of a supernova

variable star: A star whose brightness varies with time often in a regular manner

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