RR Lyrae variable stars and blue horizontal branch (BHB) stars have standard intrinsic visible-light intensities {standard lights}. Type-1a-supernova intrinsic brightness varies directly with time visible, so brighter lasts longer (galaxies have one every hundred years). Quasars have standard intrinsic ultraviolet-light intensities. Comparing observed brightness to intrinsic brightness measures object distance, because brightness decreases with distance squared.
Physical Sciences>Astronomy>Star
Outline of Knowledge Database Home Page
Description of Outline of Knowledge Database
Date Modified: 2022.0224