Coronix

Coronix, a knight in blackened iron, wears a crown of 13 broken spikes against an eclipsed Sun, each tip burning coronal green.

The Physics

The green coronal line at 530.3 nm (5302.86 Å in air), seen at total eclipses, was blamed on an unknown element, “coronium”. Walter Grotrian (1939) matched the red 637.4 nm line to Fe X, and Bengt Edlén (announced 1941, full paper in Z. Astrophys. 22, 30, 1942) identified the green line as Fe XIV: iron with 13 of its 26 electrons stripped away, Fe¹³⁺. The transition is the magnetic-dipole decay ²P°_3/2 → ²P°_1/2 inside the 3s²3p ground term, a fine-structure flip that an electric dipole cannot drive.

Fe + 13 ionisations → Fe¹³⁺ (Fe XIV)

χ(Fe¹²⁺ → Fe¹³⁺) ≈ 361 eV ≫ k_BT_photosphere ≈ 0.5 eV

• Fe XIV: spectroscopic notation for the ion with 13 electrons removed (Roman numeral = charge + 1)
• χ: ionisation energy needed to remove the 13th electron (eV)
• k_B: Boltzmann constant, 1.380 649 × 10⁻²³ J K⁻¹ (exact)
• T_photosphere: temperature of the visible solar surface, about 5800 K

Making Fe¹³⁺ in collisional equilibrium needs electron temperatures of about a million kelvin or more, so the identification proved the corona is far hotter than the surface below it. Sources: B. Edlén, MNRAS 105, 323 (1945), doi:10.1093/mnras/105.6.323; W. Grotrian, Naturwiss. 27, 214 (1939); P. Swings, ApJ 98, 116 (1943); NIST Atomic Spectra Database (Fe XIV).

Honest caveat: Why the corona is so hot (the coronal heating problem) is still unsolved; wave heating and many small reconnection events (“nanoflares”) are both studied. The ionisation-energy figure is from the NIST database and rounded.

The glow is the approximate line colour: a pure spectral colour lies outside the sRGB range a print can show.

In character

Thirteen spikes, thirteen electrons surrendered to a million-kelvin crown. They named me coronium. I am iron that refused to stay cool.

On the hoodie

Front: an eclipsed disc emblem with a green ring and pixel “XIV”. Back: Coronix in full pixel art with “FORBIDDEN. OBSERVED ANYWAY.” and “CORONIUM WAS IRON.” Gildan 18500 Heavy Blend hoodie, Black, S to 5XL.

Part of the Forbidden Transitions set with Nebulia, Flipwarden, Viridael, Sanguora, Sulphra. Browse all physics hoodies, more astrophysics & cosmology designs, or the Deep Cuts.