Page "Photometry (astronomy)" Paragraph 8

Photometric measurements can be combined with the inverse-square law to determine the luminosity of an object if its distance can be determined, or its distance if its luminosity is known.

Other physical properties of an object, such as its temperature or chemical composition, may be determined via broad or narrow-band spectrophotometry.

Typically photometric measurements of multiple objects obtained through two filters are plotted on a color-magnitude diagram, which for stars is the observed version of the Hertzsprung-Russell diagram.

Photometry is also used to study the light variations of objects such as variable stars, minor planets, active galactic nuclei and supernovae, or to detect transiting extrasolar planets.

Measurements of these variations can be used, for example, to determine the orbital period and the radii of the members of an eclipsing binary star system, the rotation period of a minor planet or a star, or the total energy output of a supernova.