PHYSICS 20E Lecture Notes - Lecture 19: Annie Jump Cannon, Stellar Classification, Big Bang
Document Summary
Stars are needed for life: stars make the atoms that are necessary for life, can keep planets warm enough for liquid water, provide a potential energy source (photosynthesis) Range from 10^-4 to 10^6 of the sun"s luminosity. Anything with a temperature shines by a process called black body radiation. Perfect black body does not reflect any light (totally black ) Two facts about black body radiation: hotter things shine with brighter intensity: i. T^4 : hotter things emit bluer light (shorter wavelength) The sun has a temperature t~5800 k. Comes around 520 nm, which is green but as sun"s light travels through atmosphere, our eyes capture it as yellow/orange. Peaks right in the middle of the visible light spectrum. Looks white from space, yellowish from earth because of atmosphere. Because we aren"t perfect black body radiators. Planets are cooler than stars so they shine in longer wavelength light (infrared) Stars are hotter, emit in shorter, visible wavelengths.
