PHYS 183 Lecture Notes - Lecture 7: Inverse-Square Law, Energy Star, Parsec
Document Summary
Stars: sun just an example, factory of nuclear fusion. Takes hydrogen and fuses it to helium in proton proton chain: many types, well defined path, born and die (not eternal) Known thanks to surveys of many stars. Census shows maximum age: cant study large lifespan but can test many different ones, very far away (#shocker) Closest star is 260k times distance to sun. Proxima centauri 4. 3 ly away = 1. 36 pc: distance to sun = 1au = 1. 5*10^11m, 1 parsec = 1 pc = 3*10^16 m, 1 light year = 1 ly = 9. 5*10^15 m = 3. 1 pc. Apparent brightness: distance is reason other stars more faint. Luminosity: amount of energy star radiates per second. Eg 100 w light bulb: 100 joules per second. Relationship between luminosity and apparent brightness is inverse square law: assumes that no matter what direction you"re looking at it emits same light. Total energy is conserved, so it gets spread out to larger area.
