Sanguora: Forbidden [O I] 630.0 nm Red Aurora Line

Cosmology & the Sky arc, page 152 of 193. Back to The Pixelated Physics Universe

Who they are

Sanguora, a tall oracle on a high spire, trails a slow red veil of light far above a thin band of green aurora.

Sanguora is a character of the Cosmology & the Sky arc: drawn in pixels, ruled by one piece of real physics, and never allowed to break it.

The physics

Atomic oxygen’s red auroral doublet at 630.0 nm and 636.4 nm is the forbidden ¹D₂ → ³P transition (to ³P₂ for 630.0 nm and ³P₁ for 636.4 nm), mainly magnetic dipole. The ¹D₂ level lives about 110 s, around 150 times longer than the green line’s upper level. Collisions therefore quench it everywhere below roughly 200 km, and the red aurora shines only from the thinnest high air. ¹D₂ is also the lower level of the 557.7 nm green line, so each green photon leaves an atom ready to emit red.τ(¹D₂) ≈ 110 sI630 ∝ P(¹D₂) · A630 / (Atot + kq[M]) τ: radiative lifetime of ¹D₂ (s) I630: 630.0 nm emission rate per unit volume (photons m⁻³ s⁻¹) P(¹D₂): production rate of ¹D₂ atoms (m⁻³ s⁻¹) A630: Einstein coefficient of the 630.0 nm branch (s⁻¹) Atot: total radiative decay rate of ¹D₂, = 1/τ (s⁻¹) kq[M]: collisional quenching rate per atom (s⁻¹)

No single equation is shown for this character; the physics above is stated in words because it is an observation or a piece of history, and we do not invent formulas.

Honest caveat: The green cascade is not the only source of ¹D₂: slow electrons and chemical reactions populate it directly. “Above about 200 km” is approximate and varies with solar activity.The glow is the approximate line colour: a pure spectral colour lies outside the sRGB range a print can show.In characterDown there the air is loud. Up here I have a hundred and ten seconds of silence, and I spend every one of them on red.

Crossovers

Sanguora meets Viridael (Forbidden [O I] 557.7 nm Green Aurora Line). Viridael's green 557.7 nm line and Sanguora's red 630.0 nm line come from the same oxygen atoms. The red state lives much longer, so it only survives high up, where collisions are rare.

Sanguora meets Nightglowe (OH Airglow). Sanguora's red glow appears high in the aurora. Nightglowe's OH airglow glows every night, aurora or not, and brightens the near-infrared sky.

Wear the lore

Concept keywords: Forbidden [O I] 630.0 nm Red Aurora Line, Sanguora, Cosmology & the Sky, physics lore, Pixelated Physics