What specific type of star did Hubble use as standard candles to accurately determine the distances to the Andromeda Nebula?

Answer

Cepheid variable stars

Hubble identified Cepheid variable stars within the Andromeda Nebula. By measuring their cyclical changes in brightness, he could accurately determine their intrinsic luminosity, which allowed for a reliable calculation of their distance from Earth.

What specific type of star did Hubble use as standard candles to accurately determine the distances to the Andromeda Nebula?
galaxyAstronomeruniverseLawcosmology