Distance Measurement in Astronomy
Since all stars appear as points of light, even with the largest telescopes, and since geometrical distance measurement by parallax is possible only for the closest stars, an overlapping chain of distance measurement techniques has been developed. The distance indicators include:
A supporting idea for distance measurement is that if a specific kind of light source is known to have a constant and dependable absolute luminosity, then the measured intensity at the detector can be used to calculate its distance. Light from a point source diminishes according to the purely geometrical inverse square law, so the number of photons into a standard area detector can be used as a distance measurement. This is often referred to as the "standard candle" approach.