As a cluster ages, the colour and brightness of its stars varies in a way that astronomers thought they understood. (newscientist.com)
Hence the only remaining problem is: How can we know the absolute brightness of a star without knowing its actual distance beforehand? (talkorigins.org)
[1] Most of the exoplanets currently known were discovered using indirect techniques — such as radial velocity variations of the host star, or the dip in brightness of the star caused by a transiting exoplanet. (sciencedaily.com)