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Universe
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space and everything that exists within it including all matter and energy
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Galaxy
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a collection of stars, gas, dust and other objects bound together by gravity
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Star
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a large body of gas which is held together by gravity and emits light and energy through nuclear fusion
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Nebula
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clouds of dust and gas; site of star formation; remains of dead or dying stars
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Main Sequence Star
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a stable star which is actively fusing hydrogen and is shown in a diagonal pattern within a H-R diagram
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HR Diagram
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a graph that shows the relationship between the brightness, surface temperature, and color of stars
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Luminosity
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total amount of light (energy) emitted by a star or other celestial body
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