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Middle: This HST image of a region of M100 shows a class of pulsating
star called a Cepheid Variable. Though rare, these stars are reliable
distance indicators to galaxies. The top three frames were taken on May
9, 4, and 31 (l to r) and reveal that the star changes brightness.
Credit: Dr. Wendy L. Freedman, Observatories of the Carnegie Institution
of Washington, and NASA
Bottom: This sequence of HST images chronicles the rhythmic changes in
the Cepheid Variable shown above, which doubles in brightness over a
period of 51.3 days.
Credit: Dr. Wendy L. Freedman, Observatories of the Carnegie Institution
of Washington, and NASA
Courtesy Space Telescope Science Institute (STScI)
