Standard star
As standard stars in the will Astronomy stable radiant fixed stars referred to as a reference for astrometric and photometric serve measurements, especially for apparent brightness , spectral type or radial velocity . A standard star must be precisely measured with regard to the relevant observation size and its stability must be ensured through long-term observations. Several standard stars define a reference system for such measured quantities and are used to calibrate the measuring instruments.
historical development
The scale of the star brightness goes back to Hipparchus' classification into 1st to 6th magnitude classes , which was refined in 1850 by a logarithmic law. This scale was related to the Pole Star until around 1950 , which received a magnitude of 2.12 mag . De facto was Vega a reference point was set for a brightness of 0.0.
When it turned out that the Pole Star is a weakly variable , the international pole sequence of around 50 stars of different brightnesses was introduced in 1922 and later expanded to 96 stars.
Today, the measurement of the brightness of stars is usually done with the help of CCD sensors and using filter systems that are to be selected depending on the application, for example the UBV system .
UBV system
The zero points for the different filter ranges of the frequently used UBV system were chosen so that the U − B and B − V color indices for an A0V star (not influenced by extinction ) become zero, i.e. the brightness of these stars in them Filter areas are identical. (A0V stars have a relatively constant intensity over the entire visual range of the spectrum.) Accordingly, a series of A0V stars is used for calibration.
The UBV system (1955) was extended to the southern sky in the 1960s through the adjustment of connecting stars in zones .
See also
Literature and Sources
- H. Zimmermann, A. Weigert: Lexicon of Astronomy , Spectrum Akadem.Verlag, Heidelberg-Berlin
- J. Bennett, M. Donahue, N. Schneider, M. Voith: Astronomie , ed. Harald Lesch , 5th edition, Pearson-Studienverlag, Munich-Boston-Harlow-Sydney-Madrid 2010
- Photoelectric UBV photometry of standard stars in the southern sky (J. Pfleiderer et al. 1966)