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The UBV photometric system (from Ultraviolet, Blue, Visual), also called the Johnson system (or Johnson-Morgan system), is a photometric system usually employed for classifying stars according to their colors. It was the first standardized photometric system.
The amount of reddening is characterized by color excess, defined as the difference between the observed color index and the normal color index (or intrinsic color index), the hypothetical true color index of the star, unaffected by extinction. For example, in the UBV photometric system we can write it for the B−V color:
A commonly adopted standardized photometric system is the Johnson-Morgan or UBV photometric system (1953). At present, there are more than 200 photometric systems. [citation needed] Photometric systems are usually characterized according to the widths of their passbands:
U−B color index +0.85 [2] B−V color index +1.10 [2] R−I color index: 0.54 Astrometry; Radial velocity (R v) −25.2 [4] km/s: Proper motion (μ) RA: +0.55 [1] ...
U−B color index: −0.86 [3] B−V color index: −0.21 [3] Variable type: ... Bellatrix was included with a set of bright stars used to define the UBV magnitude ...
The UBV catalog data format is in plain text. After uncompressing by unzip or gunzip it can be seen by any text viewers or by the online ADC viewer. Specifications for the catalog format are provided at the download sites. Original catalogue data, 1953-1985, 109293 objects (alternative reference is Mermilliod, 1987)
The DSM Yolk Color Fan is a 16-scale color index that distinguishes yolk color and is widely used in the poultry industry. Under the scale, each number corresponds with a different shade. Number ...
For example, comparisons in the B (blue) or V (visible) range lead to the so-called B-V color index, which increases the redder the star, [39] with the Sun having an index of +0.648 ± 0.006. [40] Combining the U (ultraviolet) and the B indices leads to the U-B index, which becomes more negative the hotter the star and the more the UV radiation.