{"product_id":"viridael-pixel-hoodie","title":"Viridael – The Forbidden [O I] 557.7 nm Green Aurora Line Pixel Hoodie","description":"\u003cp\u003eViridael, a hooded keeper with closed eyes, holds a single droplet of green light beneath auroral curtains that stop at a haze line.\u003c\/p\u003e\u003ch3\u003eThe Physics\u003c\/h3\u003e\u003cp\u003eThe aurora’s dominant green line at 557.7 nm, first examined spectroscopically by Anders Ångström in 1867, was identified in 1925 by J. C. McLennan and G. M. Shrum as the forbidden ¹S₀ → ¹D₂ transition of atomic oxygen, both levels inside the 2p⁴ ground configuration (an electric-quadrupole transition). The ¹S₀ level is metastable, lifetime about 0.74 s. Below roughly 100 to 120 km, collisions de-excite it before it can radiate, so the green curtain has a lower edge.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eτ(¹S₀) ≈ 0.74 s\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eLine emitted when  A ≳ k\u003csub\u003eq\u003c\/sub\u003e[M]   (quenching rate per atom below radiative rate)\u003c\/strong\u003e\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003eτ: radiative lifetime of the upper level (s)\u003c\/li\u003e\n\u003cli\u003eA: Einstein spontaneous-emission coefficient, = 1\/τ for a single decay channel (s⁻¹)\u003c\/li\u003e\n\u003cli\u003ek\u003csub\u003eq\u003c\/sub\u003e: collisional quenching rate coefficient (m³ s⁻¹)\u003c\/li\u003e\n\u003cli\u003e[M]: number density of colliding air molecules (m⁻³), which rises steeply with falling altitude\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003eStatistically the green emission peaks near 114 km. Sources: McLennan \u0026amp; Shrum, \u003cem\u003eProc. R. Soc. A\u003c\/em\u003e 108, 501 (1925), doi:10.1098\/rspa.1925.0088; \u003cem\u003eAstron. \u0026amp; Geophys.\u003c\/em\u003e 47, 1.11 (2006); Whiter et al., \u003cem\u003eAnn. Geophys.\u003c\/em\u003e 41, 1 (2023).\u003c\/p\u003e\u003cp\u003e\u003cem\u003eHonest caveat:\u003c\/em\u003e Published lifetimes for ¹S₀ range from about 0.7 to 0.8 s; we use 0.74 s. The quench altitude is a range, not a sharp line.\u003c\/p\u003e\u003cp\u003eThe glow is the approximate line colour: a pure spectral colour lies outside the sRGB range a print can show.\u003c\/p\u003e\u003ch3\u003eIn character\u003c\/h3\u003e\u003cp\u003e\u003cem\u003eHold still. I can keep this light for less than a second, and only above the noise of the crowded air. That is enough to paint the sky.\u003c\/em\u003e\u003c\/p\u003e\u003ch3\u003eOn the hoodie\u003c\/h3\u003e\u003cp\u003eFront: a green droplet in a ¹S→¹D ladder glyph. Back: Viridael in full pixel art with “FORBIDDEN. OBSERVED ANYWAY.” and “HOLD IT 0.74 SECONDS.” Gildan 18500 Heavy Blend hoodie, Black, S to 5XL.\u003c\/p\u003e\u003cp\u003ePart of the \u003cstrong\u003eForbidden Transitions\u003c\/strong\u003e set with \u003ca href=\"\/tr\/products\/nebulia-pixel-hoodie\"\u003eNebulia\u003c\/a\u003e, \u003ca href=\"\/tr\/products\/coronix-pixel-hoodie\"\u003eCoronix\u003c\/a\u003e, \u003ca href=\"\/tr\/products\/flipwarden-pixel-hoodie\"\u003eFlipwarden\u003c\/a\u003e, \u003ca href=\"\/tr\/products\/sanguora-pixel-hoodie\"\u003eSanguora\u003c\/a\u003e, \u003ca href=\"\/tr\/products\/sulphra-pixel-hoodie\"\u003eSulphra\u003c\/a\u003e. Browse all \u003ca href=\"\/tr\/collections\/hoodies\"\u003ephysics hoodies\u003c\/a\u003e, more \u003ca href=\"\/tr\/collections\/astrophysics\"\u003eastrophysics \u0026amp; cosmology designs\u003c\/a\u003e, or the \u003ca href=\"\/tr\/collections\/deep-cuts\"\u003eDeep Cuts\u003c\/a\u003e.\u003c\/p\u003e","brand":"Printify","offers":[{"title":"Black \/ S","offer_id":50964466106471,"sku":"19414848035613386043","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ M","offer_id":50964466139239,"sku":"17016648611276429798","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ L","offer_id":50964466172007,"sku":"87744045058325625784","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ XL","offer_id":50964466204775,"sku":"11275585377535559326","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ 2XL","offer_id":50964466237543,"sku":"21643665374794089763","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ 3XL","offer_id":50964466270311,"sku":"29664513403508579823","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ 4XL","offer_id":50964466303079,"sku":"20794520443654310472","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ 5XL","offer_id":50964466335847,"sku":"30785834400081188521","price":64.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0596\/8746\/9159\/files\/03_H14.png?v=1793678386","url":"https:\/\/pixelatedphysics.com\/tr\/products\/viridael-pixel-hoodie","provider":"Pixelated Physics","version":"1.0","type":"link"}