UBV photometric system
(Johnson System, Johnson-Morgan System)
(commonly-cited photometric system for describing stars' colors)
The UBV photometric system,
also called the Johnson system or Johnson-Morgan system,
is an early well-accepted photometric system and
is a system generally assumed if no other system is specified or implied.
It specifies U, B, and V passbands,
in turn, specifying specific B-V and U-B color indices.
Magnitudes are calibrated as zero for A0 V stars
unaffected by reddening.
The UBVRI photometric system, i.e.,
Johnson-Cousins system is an extension with red and
infrared passbands, R band and I band.
Referenced by pages:
north polar sequence (NPS)
rare designator prefixes
Strömgren photometric system