PHYS 183 Lecture Notes - Lecture 18: Red-Giant Branch, Solar Mass, Globular Cluster
21 Apr 2018
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Document Summary
Luminosity spans much larger range of values than temperature does. Most stars are on the main sequence. Most stars lie on the main sequence. Main sequence not equally populated: many more cool stars than hot. But cool stars hard to observe: dimmer, smaller. Most prominent stars in night sky are the rarer, most luminous ones. All stars on main sequence have as their primary energy source nuclear fusion of hydrogen. Stars off the main sequence have a different primary energy source. High mass stars are hot, bright, blue: mass ge(cid:374)erall(cid:455) relative to u(cid:374)"s (cid:373)ass. Stellar size determined by principle of hydrostatic equilibrium. Gravity that wants to pull matter inwards: pressure. Radiation and gas pushing outwards keeps balance. Equilibrium: star reaches a balance between inward crushing gravity, outward pushing gas and radiation. More massive star has greater gravity contracts, but heats up core so more nuclear reactions occur, more pressure outward, higher temperature.
