Constellation List
Star List
By Season
Alphabetical
Latitudes
Minneapolis, MN (45°N)
NorthPole (90°N)
Prudhoe Bay, AK (70°N)
St.Petersburg,
Russia(60°N)
Prague, C.R. (50°N)
Philadelphia, PA (40°N)
Albuquerque, NM (35°N)
New Orleans, LA (30°N)
Santiago, Cuba (20°N)
Caracas,
Venezuela (10°N)
Quito, Ecuador (0°N)
Port Moresby,
New Guinea(10°S)
Porto Alegre,
Brazil (30°S)
Montevideo,
Uruguay(35°S)
Queenstown, NZ (45°S)
South Pole (90°S)
Bibliography and Credits
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The Star Color Index
B - V
Apparent Magnitude
Photometry is the measurement of the brightness and color of stars. The visual or apparent magnitude of a star approximates to the brightness of the star as seen by the unaided eye. This magnitude may be designated as V for visual.
Photographic Magnitude
Currently photometry is carried out with electronic instruments, but in earlier years photometry was carried out by measuring the exposure produced by the image of a star on a photographic plate. In comparison with the response of the human eye, a photographic emulsion is relatively more sensitive to short wavelength, blue light than it is to red. Thus a blue star would produce more exposure on a photographic emulsion than would be expected from its Apparent Magnitude, while a red star would produce less. Therefore the unfiltered photographic image of a star gives a measure of a stars magnitude weighted toward the blue end of the spectrum. This is the B (for blue) or photographic magnitude. (Optical and electronic filtering allow modern electronic detectors to approximate the color response of the eye or of a photographic emulsion.)
The Color Index
The difference B - V between the two magnitude estimates is known as the "B- V color index of the star" ( or just the "color index" for short). It gives a numerical measurement of the color of a star. For blue stars will be negative, while for very red stars, it will be a positive number.
The color index correlates with both the spectral type and perceived color of the star, as shown in the following table (See Kaler, p. 80).
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Color Index
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Spectral Type
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Approximate Color
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1.41
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M0
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Red
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0.82
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K0
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Orange
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0.59
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G0
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Yellow
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0.31
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F0
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Yellowish
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0.00
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A0
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White
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-0.29
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B0
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Blue
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