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cepheid
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a star that belongs to a class of yellow supergiant pulsating stars; these stars vary periodically in brightness, and the relationship between their periods and luminosities is useful in deriving distances to them
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light curve
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a graph that displays the time variation of the light from a variable or eclipsing binary star or, more generally, from any other object whose radiation output changes with time
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luminosity class
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a classification of a star according to its luminosity within a given spectral class; our Sun, a G2V star, has luminosity class V, for example
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parallax
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an apparent displacement of a nearby star that results from the motion of Earth around the Sun
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parsec
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a unit of distance in astronomy, equal to 3.26 light-years; at a distance of 1 parsec, a star has a parallax of 1 arcsecond
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period-luminosity relation
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an empirical relation between the periods and luminosities of certain variable stars
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pulsating variable star
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a variable star that pulsates in size and luminosity
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RR Lyrae
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one of a class of giant pulsating stars with periods shorter than 1 day, useful for finding distances