Which field of study uses the spectrum of light to infer the presence of chemical elements in distant objects?

• A. Photometry
• B. Spectroscopy
• C. Astrometry
• D. Radio astronomy

Answer: (B)

Spectroscopy is the study that uses the spectrum of light to infer which chemical elements are present in distant objects. When light from a star, galaxy, or planet comes to us, atoms and ions absorb or emit photons at very specific wavelengths. Those wavelengths show up as dark absorption lines or bright emission lines in the spectrum, and each element has a unique set of lines—its spectral fingerprint. By matching the observed lines to known atomic transitions, we can identify which elements are there and estimate their abundances, even across vast distances. Photometry measures overall brightness without detailed spectral features, astrometry tracks positions and motions, and radio astronomy focuses on radio waves from various processes. So spectroscopy is the tool that links light to chemical composition.