Fraunhofer's Lines

Plate 21 speaks for itself: “The Sun's fingerprints, read in the dark gaps.”

The Physics

Fraunhofer mapped hundreds of dark lines in the solar spectrum. Each is light absorbed by atoms in the Sun's cooler outer layers at a photon energy matching one of their transitions, so the gaps identify the elements.

E = h c / λ

• E: photon energy, J
• h: Planck constant, 6.62607015×10⁻³⁴ J s (exact)
• c: speed of light, m s⁻¹
• λ: wavelength, m

Munich, 1814–15: 574 lines.

Honest caveat: Fraunhofer catalogued the lines; their atomic origin was explained by Kirchhoff and Bunsen in 1859–60.

Sources

• J. Fraunhofer, Denkschr. Akad. Wiss. München 5, 193 (1817).

On the poster

Plate 021, “Fraunhofer's Lines”: the pixel-art plate with its slogan “The Sun's fingerprints, read in the dark gaps.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.