Photometry (astronomy)
In Astronomy, the photometry indicates the study of the luminous intensity of the star S, and its variability. She is opposed to some extent to the Spectroscopie which pursues the study of the spectra stars, or to the Polarimétrie which deals with the degree of polarization of the light coming from the astronomical sources.
Photometry deals with measuring, in a spectral Bande given, the intensity of the light of a star or any other astrophysical object, and its variation in time. After subtraction of the contribution of the bottom of the sky, the luminous intensity is measured with the Fonction of spreading out of the point of star, and is compared either relatively, or in an absolute way compared to stars standards (which are known not to vary, and whose physical characteristics like the Température and the ray are known). It parmet thus to measure the Magnitude connects stars.
One uses photometry in particular in the study of the stars céphéides to measure the distance from star. The comparison of the photometry of a star given in several spectral bands makes it possible to measure its Indice of color. There exists several photometric systems to date, of which in particular that of Johnson, Kron-Cousin and Geneva (see spectral Bande).
It is to be stressed that in astronomy, photometry does not utilize the visual sensitivity of the human eye and can be very well made with invisible radiations like the Infrarouge and the Ultraviolet. On the other hand, when one moves away too much from the visible field to reach larger wavelengths (starting from the millimetre), one speaks about Radioastronomie.
See too