What do spectral lines in a spectrum indicate?

Spectral lines in a spectrum are indicative of the presence of specific chemicals, also known as elements or compounds, within an object emitting or absorbing light. When light from a star or another celestial body passes through a prism or is analyzed through spectroscopy, it produces a spectrum that displays various distinct lines. These lines result from the interaction of light with the electrons in different atoms.

Each chemical element has a unique electronic structure, leading to its own characteristic pattern of spectral lines. By identifying these lines and comparing them to known wavelengths of light emitted by substances in the laboratory, astronomers can determine which elements are present in the star or cosmic object being observed. This technique is crucial for understanding the composition of stars, galaxies, and other astronomical phenomena.

The other options relate to properties that are influenced by various factors but do not directly pertain to the identification of chemical elements. For instance, while the temperature of a star can influence the broadness of its spectral lines, it cannot be conclusively determined solely from the spectral lines themselves. Similarly, the age and distance of a star require different methods of analysis and are not indicated directly by spectral lines. Thus, the correct answer emphasizes the primary function of spectral lines as indicators of the chemical composition of astronomical objects.