Answers for the Teacher Only

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What Do You Think?

Astronomers infer the kind of atoms in stars from a careful analysis of the light the star emits. An instrument called a spectrograph spreads the light out into a spectrum, which is a photograph of the starlight at all the different wavelengths of visible light. A typical star shows a pattern of dark lines produced by the atoms in the star’s outer atmosphere. The pattern of these lines is a characteristic of the kind of atom that emitted the light.

One complication is that different kinds of atoms (different elements) are usually present together, so their spectra overlap. Another complication is the fact that the star may be moving, particularly if it is located in another galaxy. Then the position of the lines is Doppler-shifted, so the lines will not be at the same wavelength as in spectra taken in a laboratory on Earth.