Star color to temperature converter
Convert a star’s color index B−V to its surface temperature, or a temperature to the color it shows.
That's about the same as the Sun. Its light peaks at about 501.5 nm.
What it means
How hot is that star?
Ballesteros (2012) blackbody fit, for B−V from −0.4 to 2.5; real stars deviate by a few percent, and dust reddening makes stars look cooler.
Every unit
That star in every measure
Learn
Three things worth knowing
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Negative is blue
B−V near 0 is white (about 10,000 K), 0.65 yellow (Sun), 1.5 orange-red (about 4,000 K).
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Johnson’s filters
Harold Johnson and William Morgan defined the UBV filter system in 1953; it is still the standard color index.
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Red is cooler
Star colors run the opposite of taps: red stars are the coolest, blue the hottest.
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Popular star conversions
Background
About star colors
A star’s color tells its temperature. Astronomers measure it as B − V: how much fainter it is through a blue filter than a yellow-green one. Hot blue stars have negative B−V, the Sun +0.65 (about 5,800 K), cool red giants +1.5 or more.
Wien’s law gives where the light peaks: the Sun’s spectrum peaks in green near 500 nm.