Liberal astronomers have searched for ways to accurately determine the age of a star in keeping with their cosmology. A new technique called gyrochronology, which works this out based on the star’s rate of rotation, has just been announced and will be published in the Astrophysical Journal.  Knowing the age of the host star of a planetary system helps astronomers understand how planetary systems change over time.
The research shows that the rotation period of a star changes steadily and predictably in line with its age and color. Thus, by measuring two of these attributes you can determine the third. The star’s color is a visible sign of its mass or surface temperature. The age of the Sun is believed by astronomers to be 4.6 billion years  and can be used to calibrate the gyrochronology of most other stars. This apparently circular set of assumptions is, of course, vociferously contested by conservative Creationists.
Astronomers have other methods of working out a star’s age, but they have much larger uncertainties than gyrochronology. Unlike some other methods, gyrochronology can be applied to stars not found in star clusters (‘field’ stars). It is used to calculate the age of stars that burn their hydrogen fuel at a predictable and steady rate; it does not work so well for younger stars, although the researchers hope to do future work to extend the method to these.
The forthcoming NASA Kepler Mission will yield more information about the rotation period of other stars, as this is information gleaned while searching for the transit of new planets orbiting across their disks. Once researchers have more precise ages for stars, other problems of chronometry can be solved and a better study made of the way astronomical phenomena change through time, using the stars themselves as clocks.