Suns photosphere produces thermal radiation continuous spectrum absorption

Suns photosphere produces thermal radiation

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Sun’s photosphere produces thermal radiation (continuous) spectrum; absorption lines caused by atoms in Sun’s (or Earth’s) atmosphereoAnnie Jump Cannon- classified stellar spectra for Draper catalog; ordered classes by common spectrum lines (OBAFGKM)oCecilia Payne – how temperature affects strength of spectrum lines, figured out true chemical composition of the universeoStrength of spectrum lines varies with temperature: spectral class reveals star’s temp and color; hottest stars 50,000K blue; coolest stars 3,000K redMeasuring Star Diameters: determine sizes from luminosity and temperature; hotter objects brighter, bigger objects brighterHertzsprung-Russell Diagramo90% of stars on the main sequence; Upper left (hot and bright) to lower right (cool and dim); smallest (class M), largest (Class O)oStars in upper right called red giants (luminous but cool); stars in lower left called white dwarfs (hot but dim)Luminosity Classes: Class I (supergiants), class III (giants), class V (main-sequence); no class for white dwarfsMain sequence is a mass sequence; more massive stars (hotter, brighter, bluer); less massive (cooler, dimmer, redder); much larger range in luminosity than in massRegions of HR: States of stellar evolution (aging); main sequence are “adults”; Giants/supergiants are “aged”; white dwarfs are “dead”Massive main sequence stars and supergiants are rare; 90% of nearby stars are main sequence stars (70% < 0.5 Msun); less than 1% nearby are giants; <0.1% superG’s
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Lives are about the balance of gravity and pressure; gravity tries to compress star (increases with mass); pressure pushes outward, preventing collapse (increases with temp, density), when in balance called hydrostatic equilibriumWhere Stars Born: often occur in clusters, generally found near birthplaces; young stars are found near nebulae (clouds of gas and dust)Types of Nebulae; emission nebula: hot star excites gas near it to produce emission lines, dark nebula: dense clouds of gas and dust that block light from distant stars; reflection nebula: star light reflects off dust in a cool nebulaBorn in dark, cold dusty clouds called giant molecular clouds: most of gas in clouds is in form of molecules (H2,CO,..); huge 10-300 life years across; massive 10^5 massCollisions convert falling energy of the atoms into thermal energy (random motion); temperature of gas goes up; center of a fragment becomes dense, forms a protostarGas Clump Protostar  Pre-main sequence (T-Tauri) star  Main Sequence StaroProtostar (gas clump develops into disk in the center that is due to rotating incoming material, but also creates a huge outflow or jet; loses large envelope due to accretion, outflows, or stellar winds); pre-main sequence (infall of material, the jet, and stellar winds remove material from the cloud, revealing just disk of gas and dust and the forming star; produce strong winds); main sequence star (planets created during the disk phase remove the disk, leaving a main sequence star and planetary system)
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