Dr. Aaron Titus | Department of Physics, High Point University PHY1050      Astronomy of Stars, Galaxies, and the Cosmos home | WebAssign | textbook | course calendar

## temperature

The light given off by the filament of a light bulb is made up of lots of wavelengths. It's the combination of all of those wavelengths that determines the overall color of the light. If we separate the light into its continuous spectrum (using a glass prism or diffraction grating) and measure the energy output of the light per second, at each wavelength, we get a graph that looks like the one shown below.

A perfect emitter of light is called a blackbody and the graph of energy output as a function of wavelength is called a blackbody curve. The blackbody curve tells us the temperature of the light source. The images below show blackbody curves for various temperatures of the body (simulation developed by Mario Belloni).

View the blackbody curve and color of this star with temperature 2890 K.

Here's the blackbody curve for a star of temperature 4180 K. Its peak is close the edge of the visible spectrum.

This one is 4500 K.

This one is 4800 K.

This one is 5250 K.

This one is 5570 K.

This one is 6000 K.

This one is 6540 K.

This one is 7290 K.

This one is 10200 K.

What do you notice about the relationship between the wavelength of the peak and the temperature of the light source?

The hottest star has a wavelength of the peak that is in the ultraviolet. The coolest star has a wavelength of the peak that is in the infrared.

## Color of stars

The color of a star is a result of the combination of all of the colors of the visible spectrum. The height of the blackbody curve for each color tells you how much of that color in the spectrum contributes to the color of the star.

What color is a star that has a temperature of 2900 K?

What color is a star that has a temperature of 4500 K? Does the color where the peak occurs match the color of the star?

What color is a star that has a temperature of 6000 K? Does the color where the peak occurs match the color of the star?

What color is a star that has a temperature of 10000 K? Does the color where the peak occurs match the color of the star?

You should be able to look at the blackbody curve for a star and know whether it is a hot star or cool star and approximately what color it will be.

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