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Historically photometry was done with a photoelectric photometer, an instrument that measured the light intensity of a single object by directing its light on to a photosensitive cell. They have largely been replaced with CCD cameras, though photoelectric photometers are still used in special situations, such as where high time resolution is required.

At its most basic, photometry is conducted by gathering light in an optical telescope, passing the light through specialized optical filters, and then capturing the light energy on a CCD. Generally at least three different photometric images are taken, as well as images of photometric standard stars, each using different filters; and the dataA datum is a statement accepted at face value (a "given"). Data is the plural of datum''. A large class of practically important statements are measurements or observations of a variable. Such statements may comprise numbers, words, or images. Etymology T is then used to calculate physical and chemical parameters of the object.

Photometry is generally used to generate light curveIn astronomy, a light curve is a graph of light intensity as a function of time. The light is usually in a particular frequency interval or band. Light curves can be periodic, as in the case of eclipsing binaries, cepheid variables and other variables, ors of objects such as variable stars and supernova where the quantity of interest is the variation of total light energy output over time. Photometry can be used as a technique to discover exoplanetInfrared Image of a possible extrasolar planet (lower left) in the Constellation Taurus, taken by the Hubble Space Telescope. Subsequently proven to be a background star, but heavily used by the media nonetheless. An extrasolar planet (or exoplanet is a ps. By measuring the intensity of a star's light over a period of time, astronomers can examine deviations in its spectral output and determine possible causes.

See also

• spectroscopySpectroscopy is the study of spectra, ie. the dependence of a physical measure to frequency. Spectroscopy is often used in physical and analytical chemistry for the identification of substances, through the spectrum emitted or absorbed. A device for recor
• astrometryAstrometry is a part of Astronomy and deals with the positions of stars and other celestial bodies, their distances and movements. Part of astrometry involves creating the cosmic distance ladder. It is one of the oldest subfields of the science, the succe