What type of Cepheid stars were later found to be responsible for the initial underestimation of Andromeda's distance?
Answer
Type II Cepheids
Although Hubble's initial measurement was revolutionary for proving Andromeda was external, subsequent scientific refinement revealed an error in the calibration baseline derived from Leavitt's Law. Astronomers discovered that the Cepheids Hubble observed in Andromeda, like V1, were likely Type II Cepheids. The initial calibration standard used Type I Cepheids, which are intrinsically brighter. Because the Type II Cepheids Hubble measured were inherently fainter than the calibration assumed, the calculated distance of 900,000 light-years was too short, requiring later revisions to figures closer to 2.5 million light-years.
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