{"product_id":"nebulia-pixel-hoodie","title":"Nebulia – The Forbidden [O III] 500.7 nm Line Pixel Hoodie","description":"\u003cp\u003eNebulia, a veiled oracle in deep-navy robes, holds a ring of doubly ionised oxygen whose green light fills a planetary-nebula halo.\u003c\/p\u003e\u003ch3\u003eThe Physics\u003c\/h3\u003e\u003cp\u003eThe bright green nebular lines at 5006.84 Å and 4958.91 Å (air wavelengths) were long blamed on a hypothetical element, “nebulium”. In 1927 I. S. Bowen identified them as forbidden transitions of doubly ionised oxygen, O²⁺ (spectroscopic notation O III), from the metastable ¹D₂ level of the 2p² ground configuration down to the ³P₂ and ³P₁ levels. Because both levels share the same configuration and parity, an electric-dipole (E1) transition is forbidden; the lines go mainly by the much slower magnetic-dipole (M1) channel. In a lab gas, collisions empty ¹D₂ long before it can radiate. In a nebula they do not, because the density sits far below the level’s critical density.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003en\u003csub\u003ecrit\u003c\/sub\u003e = A\u003csub\u003eul\u003c\/sub\u003e \/ q\u003csub\u003eul\u003c\/sub\u003e\u003c\/strong\u003e\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eλ = hc \/ ΔE\u003csub\u003eul\u003c\/sub\u003e\u003c\/strong\u003e\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003en\u003csub\u003ecrit\u003c\/sub\u003e: critical electron density, where collisional de-excitation equals radiative decay (m⁻³)\u003c\/li\u003e\n\u003cli\u003eA\u003csub\u003eul\u003c\/sub\u003e: Einstein spontaneous-emission coefficient from upper level u to lower level l (s⁻¹)\u003c\/li\u003e\n\u003cli\u003eq\u003csub\u003eul\u003c\/sub\u003e: collisional de-excitation rate coefficient (m³ s⁻¹)\u003c\/li\u003e\n\u003cli\u003eλ: emitted wavelength (m)\u003c\/li\u003e\n\u003cli\u003eh: Planck constant, 6.626 070 15 × 10⁻³⁴ J s (exact)\u003c\/li\u003e\n\u003cli\u003ec: speed of light in vacuum, 299 792 458 m s⁻¹ (exact)\u003c\/li\u003e\n\u003cli\u003eΔE\u003csub\u003eul\u003c\/sub\u003e: energy gap between the two levels (J)\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003eBelow n\u003csub\u003ecrit\u003c\/sub\u003e nearly every excitation ends in a photon, so a weak transition can still be one of the brightest lines in the spectrum. William Huggins first saw these lines in 1864 in NGC 6543. Sources: I. S. Bowen, \u003cem\u003eNature\u003c\/em\u003e 120, 473 (1927), doi:10.1038\/120473a0; A. Fowler, \u003cem\u003eNature\u003c\/em\u003e 120, 582 (1927); NIST Atomic Spectra Database (O III).\u003c\/p\u003e\u003cp\u003e\u003cem\u003eHonest caveat:\u003c\/em\u003e “Forbidden” means strongly suppressed, not impossible. Quoted wavelengths are in air (500.68 nm); the vacuum value is slightly longer.\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\u003eI was called a new element for sixty years. I was oxygen all along, speaking only where the dark is quiet enough to hear me.\u003c\/em\u003e\u003c\/p\u003e\u003ch3\u003eOn the hoodie\u003c\/h3\u003e\u003cp\u003eFront: a three-level ladder emblem with a dashed green ¹D→³P arrow. Back: Nebulia in full pixel art with “FORBIDDEN. OBSERVED ANYWAY.” and “NEBULIUM WAS OXYGEN.” 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=\"\/hi\/products\/coronix-pixel-hoodie\"\u003eCoronix\u003c\/a\u003e, \u003ca href=\"\/hi\/products\/flipwarden-pixel-hoodie\"\u003eFlipwarden\u003c\/a\u003e, \u003ca href=\"\/hi\/products\/viridael-pixel-hoodie\"\u003eViridael\u003c\/a\u003e, \u003ca href=\"\/hi\/products\/sanguora-pixel-hoodie\"\u003eSanguora\u003c\/a\u003e, \u003ca href=\"\/hi\/products\/sulphra-pixel-hoodie\"\u003eSulphra\u003c\/a\u003e. Browse all \u003ca href=\"\/hi\/collections\/hoodies\"\u003ephysics hoodies\u003c\/a\u003e, more \u003ca href=\"\/hi\/collections\/astrophysics\"\u003eastrophysics \u0026amp; cosmology designs\u003c\/a\u003e, or the \u003ca href=\"\/hi\/collections\/deep-cuts\"\u003eDeep Cuts\u003c\/a\u003e.\u003c\/p\u003e","brand":"Printify","offers":[{"title":"Black \/ S","offer_id":50964464762983,"sku":"23364393242333113942","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ M","offer_id":50964464795751,"sku":"86037443440874778334","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ L","offer_id":50964464828519,"sku":"18292876638205299572","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ XL","offer_id":50964464861287,"sku":"24641802712931612922","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ 2XL","offer_id":50964464894055,"sku":"48639394253285931488","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ 3XL","offer_id":50964464926823,"sku":"67718269315531573106","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ 4XL","offer_id":50964464959591,"sku":"12022848020915244183","price":64.99,"currency_code":"USD","in_stock":true},{"title":"Black \/ 5XL","offer_id":50964464992359,"sku":"24807988142212132362","price":64.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0596\/8746\/9159\/files\/03_H02.png?v=1793678357","url":"https:\/\/pixelatedphysics.com\/hi\/products\/nebulia-pixel-hoodie","provider":"Pixelated Physics","version":"1.0","type":"link"}