Final answer:
Spectra are produced because electrons emit and absorb photons at specific wavelengths, which correspond to energy changes in the atom. Using this information, astronomers can determine the composition of stars and other celestial bodies.
Step-by-step explanation:
Spectra occur because electrons emit and absorb photons with only certain wavelengths. The spectra of different elements and ions tell astronomers about the elements themselves and the physical conditions of the astronomical bodies being observed. For example, when observing an emission spectrum, the position and brightness of the lines represent discrete energy level differences in atoms. The Bohr model of the atom explains why atoms absorb or emit energy at only specific wavelengths; only photons with energies that match the energy difference between the electron orbits can be absorbed or emitted.
Each element has a characteristic set of energy levels, and transitions between these levels involve specific wavelength changes that are observed as lines in the spectrum. When electrons jump to a higher energy level by absorbing photons, they produce an absorption spectrum, characterized by dark lines at certain wavelengths. Conversely, when electrons drop to a lower energy level and release photons, an emission spectrum can be observed, which appears as colorful lines on a black background.