Spectral Fingerprints

Pass starlight through a prism and you see a rainbow with dark lines slashed across it. These absorption lines reveal which elements are in the star's atmosphere. Each dark line corresponds to a specific photon energy absorbed by a specific element.

In 1868, French astronomer Pierre Janssen spotted an unknown bright yellow emission line in the Sun's chromosphere during a total eclipse. The eclipse mattered: blocking the Sun's blinding glare let that faint glow show.