Photometry ( dr. Greek φῶς , genitive φωτός - light and μετρέω - I measure) is an area of astronomy that develops methods and techniques for measuring the flux or intensity of electromagnetic radiation of an astronomical object [1] . As a rule, using photometry, it is possible to make measurements in large wavelength ranges of electromagnetic radiation. In the case when not only the amount of radiation is measured, but also its distribution by wavelengths is carried out, the term spectrophotometry is used .
Content
Methodology
The methods used to perform photometry depend on the wavelength and mode under study. In the simplest version, photometry is carried out by collecting radiation through a telescope . In addition, it is possible to pass the received electromagnetic radiation through specialized optical filters, with the subsequent capture and recording of light energy using photosensitive instruments. A set of bands (filters) are included in the concept of a measurement system.
Historically, photometry in the near infrared and longwave ultraviolet spectral regions was carried out using a photometer , a photoelectric device designed to measure light intensity from the same object, directing its beam to a photosensitive element. These photometers were subsequently mostly replaced by devices created on the basis of CCD cameras [2] , which can simultaneously capture images of several objects. However, photovoltaic photometers are still used in some cases, for example, when high resolution is not required.
In the years 1896-1898, Schwarzschild worked as an assistant at in Vienna [3] , where he developed a formula for determining the exposure time for astronomical photometry and discovered the phenomenon of non-interchangeability in photography, later named after him ( Schwarzschild effect ) [3] . In 1899 he returned to the University of Munich , where he received the post of privat-docent , defending a habilitation thesis on star brightness measurements [3] .
In 1901-1909, Schwarzschild became an ordinary, that is, a full professor at the University of Gottingen and at the same time director of the [3] . At this time, Schwarzschild was engaged in geometric optics, performed a large survey of photographic stellar magnitudes, and established a distinction between photographic and visual stellar magnitudes.
Application
- Other physical properties of the object, such as temperature or chemical composition, can be determined using spectrophotometry. As a rule, spectrophotometric measurements of several objects are obtained using two filters and the construction of a color – magnitude diagram.
- Photometry is also used to study the light variation of objects, such as variable stars, small planets, active galactic and supernova nuclei, or to detect planets located outside the solar system . Measurements of these deviations can be used, for example, to determine the period of revolution and the radii of the members of an eclipsing binary star system, the periods of revolution of small planets or stars, or the total burst of energy of a supernova.
See also
- Optical astronomy
- Infrared astronomy
- Ultraviolet astronomy
- Radio astronomy
- X-ray astronomy
- Gamma astronomy
Notes
- ↑ Sterken, Christiaan; Manfroid, J. (1992), Astronomical photometry: a guide, Astrophysics and space science library 175, Springer, pp. 1–6, ISBN 0-7923-1653-3
- ↑ Flux Photometry - Lecture 7: "Starlight, Starbright." Stellar Brightness, Astronomy 162: Introduction to Stars, Galaxies, & the Universe, Prof. Richard Pogge
- ↑ 1 2 3 4 JJ O'Connor and EF Robertson. Karl Schwarzschild MacTutor History of Mathematics archive . Date of treatment November 22, 2015. Archived November 17, 2015.