| Astrophysics (Index) | About |
Stellar distance determination, the determination of the distance to a star, uses the shorter cosmic distance ladder methods, i.e., those applicable within the Milky Way. Parallax is the certain method up to the angular resolution accuracy of astrometry: optical observations from opposite ends of Earth's orbit are used to determine the triangle from those two points to the observed star. This continues to improve with improvements in angular resolution and astrometry, and with current space astrometry (Gaia), provides useful data at thousands of parsecs.
When stellar luminosity determination produces a reasonable estimate, its luminosity distance provides a corresponding distant estimate. Spectroscopic parallax bases this on the typical luminosity of specific spectral types. (Despite its word "parallax", it is like parallax only in that it is a means of measuring distance.) Binary stars, depending upon the circumstance, may reveal mass and radius information, providing clues. Certain types of stars such as Cepheid variables provide luminosity information, through characteristics of pulses and/or spectral signatures. Given one or more stellar distance determinations of stars within a stellar cluster, it serves as a rough determination of distances to the rest of the cluster's stars. An estimate of the luminosity of cluster members can also make use of the group's characteristics, through main sequence fitting.
Stellar distance determinations generally have considerable uncertainty, and presumed distances are often revised, and additional independent and improved determinations generally remain of interest. A new determination as much as 30% different than earlier is not uncommon.