For 100 years astronomers have paid particular attention to a class of variable star known as the Cepheids.
过去100年来，天文学家特别注意一类称作“仙王座变光星”的恒星。
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And, since individual Cepheids are bright enough to be seen in other galaxies, they were the first tool used to estimate the distances to such galaxies.
Cepheids are a special type of star that pulsates in a predictable way, and like the type 1a supernova, they are assumed to be the same, no matter where they are located.