What is Spectral analysis?

Example 2.20 (The Sun’s recipe)

The solar spectrum carries thousands of dark lines, mapped by Fraunhofer in 1814. Among the strongest: $410$, $434$, $486$ and $656\,\mathrm{nm}$ — the full hydrogen fingerprint — together with the sodium line at $589\,\mathrm{nm}$ and a calcium pair at $393$ and $397\,\mathrm{nm}$. The Sun’s atmosphere contains hydrogen above all, plus traces of elements familiar from Earth’s rocks. Modern measurements refine the headline: the Sun is roughly three quarters hydrogen by mass.