A star used to calibrate observations of previously unstudied stars, particularly for photometry. In spectrophotometry, standard stars are compared with a black-body source located close to the telescope so that the amount of radiation emitted at each wavelength is known. In conventional photometry, standard stars have accurately known magnitudes and colours, against which stars under study are compared. Each system of photometry (e.g. Johnson, Kron–Cousins RI, or Strömgren photometry) has its own set of standards which have been carefully intercompared. Standard stars must be bright enough to be easily observable with small telescopes, but not so bright as to saturate photometers on large telescopes.
Subjects: Astronomy and Astrophysics.