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How can spectroscopy identify the chemical composition of stars and other materials?

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A horizontal gradient bar displays the visible light spectrum from violet to red, labeled with corresponding frequency in terahertz, wavelength in nanometers, and photon energy in electron volts. — light When white light is spread apart by a prism or a diffraction grating, the colours of the visible spectrum appear. The colours vary according to their wavelengths. Violet has the highest frequencies and shortest wavelengths, and red has the lowest frequencies and the longest wavelengths.

Spectroscopy identifies the chemical composition of stars and other materials by analyzing the specific wavelengths of light they emit or absorb. This method relies on the principle that every element possesses a unique set of quantum states, and when atoms transition between these energy levels, they emit or absorb radiation at characteristic frequencies.1234

In emission spectroscopy, atoms are excited—often by heat or electrical discharge—causing them to release energy as light at specific wavelengths. By dispersing this light into a spectrum using a prism or grating, scientists can observe these distinct spectral lines to identify the elemental composition of a substance.143

For stars, this process is applied to analyze their atmospheres. When light from a star's interior passes through its cooler outer layers, the gases there absorb specific wavelengths, creating dark lines (known as Fraunhofer lines) in the spectrum. By comparing these observed lines to known laboratory standards, astronomers can determine the temperature, density, and chemical makeup of stellar atmospheres. This technique is highly sensitive, allowing for the detection of elements even in trace amounts.45612