Cepheid variable stars were the key instrument in Edwin Hubble's 1923 conclusion that M31 (Andromeda) was an external galaxy, as opposed to a smaller nebula within the Milky Way.
Cepheide variable stjerner var det vigtigste redskab i Edwin Hubble’s konklusion fra 1923 at M31 (Andromeda) var en ekstern galakse og ikke en mindre tåge i Mælkevejen.