What specific class of pulsating stars served as the essential 'standard candle' for measuring immense cosmic distances?

Answer

Cepheid variables

Cepheid variables were the key standard candles because Henrietta Swan Leavitt established a relationship between their pulsation period and their intrinsic brightness, allowing distance calculation.

What specific class of pulsating stars served as the essential 'standard candle' for measuring immense cosmic distances?
measurementgalaxyAstronomerDistancecalculation