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When astronomers describe a star as billions of years old, how do they estimate that age if the star is still shining and can’t be examined up close? I understand that a star’s brightness and color reveal some of its properties, but I’m unsure how those observations translate into an age.
Do researchers mainly compare a star with models of how stars change over time, or are there independent clues that help check the estimate? I’d especially like to understand how this works for stars that are not part of a cluster, where there’s no obvious group to compare them with.
