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What Is the Relationship of the Colors & the Temperatures of the Stars?

At first glance, the stars in the sky all appear to be white, but closer observation reveals that stars have a variety of colors, such as white, blue, red and yellow. Until two centuries ago, the reason for this color variation was not understood, but when physicists and astronomers understood the properties of matter at very high temperatures, they realized that the color of a star was directly related to its temperature.

Classifying Stars
- Scientists classify stars into six categories based on a star's temperature range from hottest to coolest. This color-temperature sequence corresponds with a reverse rainbow, with the hottest, or "O," stars appearing blue and the coolest, or "M," stars appearing red. In degrees Fahrenheit, "O" stars are 50,000 to 100,000, "B" stars are 17,500 to 50,000, "A" stars are 13,000 to 17,500, "F" stars are 10,500 to 13,000, "G" stars are 8,500 to 10,500, "K" stars are 6,000 to 8,500 and "M" stars are 3,000 to 6000.
Source of a Star's Light
- A star's surface heat determines the color of light emitted.
  
  Observing a star's light and color helps determine its temperature. Visible starlight is created by light being emitted from the surface of a star. The heat energy radiated or the star's average surface temperature directly influences the color of the visible light emitted from the star. Most stars, called "main sequence stars," generate this heat through nuclear fusion, converting hydrogen to helium.
Star Colors and Classifications
- A more exact relationship between the surface temperature of a star and its color can be found by viewing tables such as Enchanted Learning's chart of Spectral Classes on its Star Types Web page or Clark Planetarium's Star Color Visual Chart. From this chart, we learn that stars in classes O, B, A and F can appear blue; stars in classes F and G can appear white; stars in class G can appear yellow; stars in class K can appear orange; and stars in classes K and M can appear red.
Familiar Stars
- The sun is average in age, size and temperature compared with other stars.
  
  The sun of our solar system is a middle-aged, white-yellow, G-type star about 4.6 billion years old with a temperature averaging 10,000 degrees Fahrenheit. Sirius, or "The Dog Star," is the brightest star in our sky besides the sun, and is a blue, A-type, main-sequence star that is about 70 times as bright as our sun. Betelgeuse is a red M-type star that is about 14,000 times brighter than our sun.

Astronomy