| barred spiral galaxy | A spiral galaxy in which the nucleus is crossed by a bar. The spiral arms start at the ends of the bar.
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| elliptical galaxy | A galaxy having an ellipsoidal shape and lacking spiral arms.
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| galactic cannibalism | The capture and disruption of one galaxy by another.
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| Hubble’s constant (H) | The rate at which the recession speeds of galaxies increase with distance. Current estimates of Hubble’s constant range from 50 to 100 kilometers per second per megaparsec.
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| Hubble’s law | The linear relationship between the recession speeds of galaxies and their distances. The slope of Hubble’s law is Hubble’s constant.
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| irregular galaxy | A galaxy having an amorphous shape and lacking symmetry.
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| normal spiral galaxy | A galaxy in which the spiral arms emerge from the nucleus.
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| primary distance indicator | A type of object, such as a Cepheid variable, for which we know the size or brightness by observing them in the Milky Way.
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| secondary distance indicator | A type of object for which we know the size or brightness because objects of that type have been found in nearby galaxies.
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| spiral galaxy | A flattened galaxy in which hot stars, interstellar clouds, and other young objects form a spiral pattern.
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