lecture23 - Astronomy Picture of the Day Nebulae in the...

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Astronomy Picture of the Day Nebulae in the Cygnus region of the Milky Way
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The spectrum of starlight A star’s spectrum is close to a black-body curve, with absorption lines imprinted on it by elements in the star’s photosphere
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The spectral sequence: history In the late 1800s and early 1900s, the Harvard College Observatory employed women to perform measurements and compile data from photographic plates The spectral sequence used today comes from Annie Jump Cannon’s work
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The “Balmer Series” of spectral lines from hydrogen: Transitions between the n=2 level and higher energy levels
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The spectral sequence: history Cannon sorted stars by the strength of their absorption lines from hydrogen (the Balmer series lines) Stars with the strongest hydrogen lines were “spectral type A”, next strongest were type “B”, etc. Some letters were eventually discarded from the sequence H α H β H γ H δ The Balmer series of Hydrogen
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The spectral sequence: history Cannon’s important discovery: the strength of the hydrogen lines depends on the star’s surface temperature Stars with temperature around 10,000 K have the strongest hydrogen lines H α H β H γ H δ The Balmer series of Hydrogen
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The spectral sequence: history The sequence was re-ordered as a sequence from hottest to
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This note was uploaded on 11/23/2010 for the course PHYSICS PHYSICS 20 taught by Professor Aaronbarth during the Winter '10 term at UC Irvine.

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lecture23 - Astronomy Picture of the Day Nebulae in the...

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