It works basically like that. The spectrum of the star will be an absorption spectrum. The star produces a continuous spectrum and then the atoms in its atmosph

It works basically like that. The spectrum of the star will be an absorption spectrum. The star produces a continuous spectrum and then the atoms in its atmosphere absorb specific wavelengths. The light then travels through the planet's atmosphere where other atoms and molecules absorb other wavelengths; the signatures of which are known, telling scientists the makeup of the atmosphere.