6 - EM Radiation from Stars

6 - EM Radiation from Stars - E-M radiation for *s last...

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E-M radiation for *’s last time – Black-body (Planck) radiation -- continuous at all λ emission depends only on T 1) hotter surface emits more at all λ 2) peak at shorter λ as T rises 3) total emission per cm 2 sec -1 = σ T 4
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Analyzing Starlight
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more precisely setup for spectroscopy : or grating detector
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Quantum transitions : => only discrete orbits/energies if atom transitions between 2 states (1,2) ==> must emit/absorb energy = Δ E 1-2 possible transitions : collisional excitation/deexcitation radiative absorption spontaneous emission stimulated emission all are probablistic, not deterministic ! Δ E = E Fnal - E initial = h ν (radiation) , 1/2 mv 2 (collisional) Hydrogen e - p +
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absorption of photon excited state of atom atomic decay w/ photon emission w/i ~10 -6 sec h ν = Ε upper - E lower 3 radiative processes : photon absorption spontaneous decay w/ emission of photon stimulated emission 2 collisional processes : collisional excitation collisional de-excitation Δ E = E Fnal - E initial = h ν (radiation) , 1/2 mv 2 (collisional) laser/ maser
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Spectrum you see depends on viewing angle !
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Energy levels of Hydrogen w/ emission processes visible ultraviolet near infrared
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6 - EM Radiation from Stars - E-M radiation for *s last...

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