noun
spectral line
Technical term in physics for a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range.
スペクトル線の観測から、星の化学組成がわかる。
From the observation of spectral lines, we can determine the chemical composition of a star.
スペクトル is the general term for 'spectrum', while スペクトル線 specifically refers to the lines within a spectrum.
Compound of スペクトル (from English 'spectrum') and 線 (line).