Nucleocosmochronology

Nucleocosmochronology or nuclear cosmochronology is a technique used to determine timescales for astrophysical objects and events.

To calculate the age of formation of astronomical objects, the observed ratios of abundances of heavy radioactive and stable nuclides are compared to the primordial ratios predicted by nucleosynthesis theory.

Nucleocosmochronology has been employed to determine the age of the Sun ($4.57$ billion years) and of the Galactic thin disk ($8.8$ billion years),  among others. It has also been used to estimate the age of the Milky Way itself by studying Cayrel's Star in the Galactic halo, which due to its low metallicity, is believed to have formed early in the history of the Galaxy.

Limiting factors in its precision are the quality of observations of faint stars and the uncertainty of the primordial abundances of r-process elements.