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Published byGodfrey Luke Osborne Modified over 9 years ago
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Stars Star field taken with Hubble Space Telescope
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Hertzsprung–Russell diagram
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Pleiades
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Star Massive, luminous ball of plasmaplasma Held together by gravity Shines due to thermonuclear fusion of hydrogen in its corethermonuclear fusion
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Betelgeuse
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Spectra of stars Allow astronomers to determine a star’s: Composition Luminosity Velocity Mass
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Spectrum of the Sun
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3 types of spectra
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1.Continuous- produced by a glowing body 2. Absorption line (dark line)- produced when a cooler gas lies between observer and glowing body – this is the type used to ID stars 3.Emission line (bright line)- emission from a glowing gas, used to study nebulae
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Star classification Stars are all made of the same material Spectral differences are due to temperature
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Coolest stars are red, hottest stars are blue
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Classification system O B A F G K M O hottest M coolest
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H R (Hertzsprung Russell) Diagrams Stars plotted according to: 1.Luminosity (absolute magnitude) – brightest stars at the top 2.Temperature (spectral class) – hotter stars to the left
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H R Diagram (cont.) 1.Main sequence – Band from hot (blue) to cool (red) – 90% of stars – e.g. the Sun 2.Giants – Luminous and cool – 10-100x size of the Sun – e.g. Aldebaran in Taurus
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3.Super Giants – 1000x larger than the Sun – e.g. Betelguese in Orion Antares in Scorpius
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4.White Dwarfs – Very hot, but low luminosity due to small size – e.g. Sirius B – NO fusion in core, glow due to contraction? Gravitational forces
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Binary star http://www.astronomy.ohio- state.edu/~pogge/TeachRes/Movies162/#spbin http://www.astronomy.ohio- state.edu/~pogge/TeachRes/Movies162/#spbin http://www.calvin.edu/~lmolnar/anim/algol.html
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Albireo (the Cal star)
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Stellar Evolution
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Fusion
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Carbon-carbon fusion
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supernova
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http://www.pbs.org/wgbh/nova/origins/progra m-3114.html
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http://www.youtube.com/watch?v=8CtjhWhw2I8
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Stellar Evolution Stars do not live forever Eventually nuclear fuel runs out and star dies
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Stages of Stellar Evolution 1.Pre-main sequence – Stars form in a dense, cool cloud of dust and gas – Gravitational attraction causes it to start to glow – NO fusion yet Protostar
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Once fusion starts the star enters the main sequence
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Types of stars http://cas.sdss.org/dr6/en/proj/basic/spectraltypes/ http://cas.sdss.org/dr6/en/proj/advanced/spectraltyp es/
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http://hubblesite.org/gallery/behind_the_pictures/mea ning_of_color/
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http://www.windows2universe.org/the_universe/ Stars/magnitude_scale.html
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Stages of Stellar Evolution (cont.) The Main Sequence – Once fusion starts the star enters the main sequence – The more massive the star the faster this process – Our Sun took about 50 million years to form
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Stages of Stellar Evolution (cont.) Main Sequence (cont.) – When the force of gravity balances the pressure force the star becomes a stable main sequence star Hydrostatic equilibrium
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Stages of Stellar Evolution (cont.) Main sequence (cont.) – Higher temp greater luminosity shorter life span – Our Sun will fuse hydrogen (burn) for about 10 billion years
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Stages of Stellar Evolution (cont.) Post-Main sequence – Hydrogen core starts to run out contraction heats up outer shell hydrogen fusion increases Red Giant Star
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Stages of Stellar Evolution (cont.) Low mass stars (e.g. the Sun) Red Giant Stars High mass stars (e.g. Betelguese) Super Giant stars
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Stages of Stellar Evolution (cont.) Death of a star – 4 solar masses or less Contraction of core heats up outer layer expands ejected into space Planetary Nebula core becomes white dwarf
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Stages of Stellar Evolution (cont.) Death of a star – More than 4 solar masses Core contraction causes fusion up to iron rapid contraction of core rebound and tremendous expansion and shock wave that blows apart star Supernova
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Stages of Stellar Evolution (cont.) Supernova Outshines all the other stars in the galaxy combined Nucleosynthesis of elements heavier than iron
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Stages of Stellar Evolution (cont.) 5-10 solar mass star neutron star (a paper clip worth of a neutron star would weigh more than Mt. Everest Emit strong radio waves Pulsar
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Stages of Stellar Evolution (cont.) Stars of 10 solar masses or more may become a black hole Mass is squeezed into a singularity Area that sparates a black hole from the surrounding space is the event horizon
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