How do astronomers verify the composition of distant stars without retrieving physical samples?

Analyzing light spectrum absorption lines matching known atomic transitions on Earth

Since physically interacting with or sampling distant celestial bodies is impossible, verification relies heavily on consistency across different methods, particularly analyzing light. When astronomers study the light spectrum emitted by a distant star, they look for specific dark lines, known as absorption lines. The presence and specific location of these lines directly correspond to the energy absorbed by specific elements within the star's atmosphere. If these observed spectral signatures match the known atomic transition patterns for elements already tested and cataloged in laboratories on Earth, the composition of the distant star is considered verified.