Thermal Radiation Curves
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Thermal Radiation Curves

If you graph the intensity (that is, the amount) of thermal radiation given off by a star as a function of wavelength, you will get a graph like this:

These curves are called "thermal radiation curves." The red curve shows thermal radiation as a function of wavelength for a star at 3730 C (6750 F). The blue curve shows a star at 5730 C (10,350 F) - a little hotter than the sun. The green curve shows a star at 7730 C (14,400 F).

The curves show that hotter stars give off more thermal radiation, just as the hot plate glowed brighter as you heated it up. The curves also show that the peak wavelength of the thermal radiation (the thin black line) moves to shorter wavelengths as the temperature increases. The 3730 C star has a peak wavelength near the border between red and infrared light. The 5730 C star has a peak wavelength in the blue wavelength of light. The 7730 C star has a peak wavelength in ultraviolet light.

Explore 3. This interactive Java applet will help you learn how thermal radiation curves change with temperature. Click on the link to open a new window, then read the instructions. Try several different temperatures and peak wavelengths. Can you find a mathematical relationship between temperature and peak wavelength?