Final answer:
A stellar spectrum comprises both absorption and emission lines, which provide insights into a star's chemical composition, motion, and physical properties.
Step-by-step explanation:
Any stellar spectrum consists of two primary components: absorption lines and emission lines. Absorption lines are created when light from the hot, dense interior of a star passes through its cooler outer layers, resulting in certain wavelengths being absorbed by the atoms present. This leads to the appearance of dark lines in the spectrum. Emission lines, on the other hand, occur when atoms in the star's atmosphere or surrounding area become excited and release energy at specific wavelengths, generating bright lines in the spectrum.
Through careful analysis of the spectrum, astronomers can determine a lot about a star, including its chemical composition, radial velocity indicated by the Doppler effect, rotational velocity, and proper motion. A star's spectrum also varies based on its temperature and the relative abundance of elements it contains. For example, nearly all stars are composed primarily of hydrogen and helium, with varying amounts of heavier elements. The precise spectral features enable astronomers to classify stars into different spectral types and understand their physical characteristics.