Aurora, Line by Line

Plate 77 speaks for itself: “Green is oxygen at 557.7. Red is oxygen higher up.”

The Physics

Auroral colours are atomic lines. Oxygen's green 557.7 nm line dominates lower down; its red 630.0 nm line comes from a long-lived state that survives only where collisions are rare, higher up.

λ = h c / ΔE

• λ: wavelength, m
• h: Planck constant, J s
• c: speed of light, m s⁻¹
• ΔE: transition energy, J

Green: O I 557.7 nm, ~100–200 km. Red: O I 630.0 nm, peaking ≈ 220–300 km.

Sources

• A. Vallance Jones, Aurora (1974).
• NIST Atomic Spectra Database (O I).

On the poster

Plate 077, “Aurora, Line by Line”: the pixel-art plate with its slogan “Green is oxygen at 557.7. Red is oxygen higher up.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.