Chapter 19

Cepheid

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

light curve

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

luminosity class

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

parallax

an apparent displacement of a nearby star that results from the motion of Earth around the Sun

parsec

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

period-luminosity relation

an empirical relation between the periods and luminosities of certain variable stars

pulsating variable star

a variable star that pulsates in size and luminosity

RR Lyrae

one of a class of giant pulsating stars with periods shorter than 1 day, useful for finding distances