LearnLight & spectraSome maths

Spectral lines

Sharp bright or dark features in a spectrum, produced when electrons in atoms jump between fixed energy levels.

Why it matters

Lines are fingerprints. They identify which elements are present, and because their rest wavelengths are known exactly, any shift measures motion.

In practice

Narrowband filters isolate single emission lines — Hα at 656.3 nm, OIII at 500.7 nm — which is why they cut through light pollution that is spread across the whole spectrum.

Rests on

Blackbody radiationThe characteristic spectrum any warm, opaque object emits, whose shape depends only on its temperature.

Leads to

Doppler shift and redshiftMotion along the line of sight stretches or compresses the wavelength of light, moving spectral lines toward the red or the blue.
Spectral classificationThe sequence O B A F G K M, ordering stars from hottest and bluest to coolest and reddest by the lines in their spectra.