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Light from Stars

The graphs below are idealized versions of the graphs you thought about in Question 1. They show how the amount of light emitted by a star should vary with the light's wavelength. The curves show the amount of light emitted as a function of wavelength for two stars: one with a peak wavelength of 4000 Angstroms (top) and one with a peak wavelength of 6400 Angstroms (bottom).

Stars whose light has peak wavelengths of
4000 Angstroms (top) and 6400 Angstroms (bottom)

Question 2. What colors would these two stars appear to your eyes?

 

So analyzing the wavelengths of light that stars give off offers an answer to the question from the last section: stars appear different colors because they emit light with different proportions at different wavelengths.

Question 3. Some stars have peak wavelengths in the infrared part of the spectrum, longer than red light. Can you still see these stars? Why or why not? What color do they appear? What about stars whose peak wavelengths are in the ultraviolet?

Explore 3. What about stars whose peak wavelength is green light? What color do they appear?

To find out, look through the SDSS database to find a few stars that emit most of their light in the green wavelength (that is, stars whose g magnitude is less than its other magnitudes. Look on your own, but if you can't find any, here is a hint. What color do these stars look to you? Was this what you expected?

Launch the Navigation Tool

Question 4. Why do stars whose peak wavelengths lie in the green range look the way they do?

HINT: Look at the visible spectra in the curves above and think about your answer to Question 3.

The Big Question

Now you see that stars look to be different colors because they have different peak wavelengths of radiation. But you might be wondering why stars have different peak wavelengths in the first place. Similarly, since all you can ever know about a star is the light that arrives on Earth, can you use a star's peak wavelength to learn something important about the star? Yes, you can. Click Next to find out how.

 

Light curves adapted from Blackbody radiation physlet, Davidson College.