MadSci Network: Astronomy

Re: Why do stars have different colors?

Area: Astronomy
Posted By: George Delange, Secondary School Teacher Science/Math, Phoenix ZUnion High School District
Date: Tue Jan 21 05:04:59 1997

Hi Heather,

Stars shine with different colors. Some are a brilliant blue-white and some appear reddish. The colors which the stars shine are determined by the temperature of the surface layers of the stars, where the light we see is given off.

Perhaps you have heard the terms "white hot and red hot." These terms refer to the appearance of metal when it is heated to different temperatures. White-hot metal is hotter than red-hot metal. We can think of the colors of stars in the same way. Astronomers accurately can determine the temperature of a star by the color it gives off.

Stars and other things, like light bulbs, give off light and other radiation because they are hot. This radiation is given off in all kinds of waves. These waves differ according to their length. The light that we see is only a small portion of of the radiation that is given off. The light that we see is called the visable part of the electromagnetic radiation spectrum. White light is the result of seeing all of the colors of light in the electromagnetic spectrum put together. Raindrops and prisms can separate white light into its different colors. Rainbows are good examples of this separating of white light into it's various colors.

Stars too give off light in all colors (wavelengths) of the electromagnetic spectrum as well as in some wavelengths of the electromagnetic spectrum that we cannot see. We find that the wavelengths are determined by the temperatures of the surfaces of the stars. We find that stars with a surface layer brightness of about 3,000K degrees are reddish. Stars of about 4,000K degrees are orange. Stars of about 6,000K degrees are yellow, like our sun. Stars of about 10,000K degrees are white and stars of about 20,000K to 30,000K degrees are blue.

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