How did Hubble use cepheids to measure the distance to M31 and other galaxies?

Answer 1

Cepheids are standard candles..They have a relation between their luminosity and pulsation period..

Thus, they can serve as indicators of distance. If luminosity is known, the distance to the galaxy can be computed using the inverse square law.

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Answer 2

Christopher Ales

The Cepheid variable stars were Hubble's "standard candles" for measuring distances: their absolute brightness was determined by measuring their apparent brightness from Earth, which he then converted to a distance using the inverse square law of light. The period of variation in brightness of the Cepheids in M31 was then observed and compared to similar stars whose distances were known.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.