E.1.6—Spectra and composition

Treat a spectrum as a fingerprint

Each element has a characteristic set of emission and absorption wavelengths because its allowed energy differences are unique. The pattern can therefore identify the chemical species producing or absorbing the light.

Use comparison evidence

Record the observed spectral lines and compare their wavelengths or frequencies with laboratory spectra of known elements. Matching several characteristic lines supports the identification.

Apply it to stars

Light from a star can contain absorption lines produced by cooler gases in its atmosphere. Comparing those lines with known spectra reveals which elements are present, even when the source cannot be sampled directly.

Common trap

Do not identify an element from one broad colour alone. The evidence is the set of matching spectral lines and their wavelengths.