How did the observation of Cepheid variable stars impact the measurement of the Hubble constant?

They allowed for precise distance calculations to distant galaxies, narrowing the age of the universe to approximately 13.8 billion years.

Cepheid variable stars function as cosmic lighthouses because their pulse rate is linked directly to their brightness. By observing these predictable pulses, astronomers are able to calculate their distance from Earth with high accuracy. Before these measurements, estimates for the age of the universe varied wildly, creating a paradox where the universe appeared younger than its oldest stars. Establishing this distance measurement provided a consistent standard for the expansion rate of the universe, resolving the uncertainty and grounding cosmological models in a more reliable timeline.