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How do astronomers use spectroscopy to determine the chemical composition of stars?

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Astronomers use spectroscopy to determine the chemical composition of stars by analyzing the light emitted by their atmospheres. This technique relies on the principle that every chemical element, when heated to incandescence, emits light at a specific, characteristic pattern of wavelengths.123

When light from a star passes through its cooler outer atmospheric layers, the gases absorb specific wavelengths that correspond to the elements present, creating dark lines in the star's spectrum known as Fraunhofer lines. By comparing these observed absorption patterns with known laboratory standards, astronomers can identify the specific elements—such as hydrogen, helium, calcium, and iron—present in the star.34

To interpret these spectra accurately, scientists must also account for the star's temperature and density, as these physical conditions influence thermal ionization and the resulting appearance of spectral lines. Through high-resolution spectral analysis, researchers can quantitatively determine the chemical makeup of stars across various spectral types.142