Telescopes collect more light than our eyes- light collecting area. Telescopes can see more detail than our eyes- angular resolution. Telescopes/instruments can detect light that is invisible to our eyes (e. g. , radio, infrared, ultraviolet, x-rays, gamma-rays) The minimum angular separation that the telescope can distinguish. Nuclear potential energy (core) / luminosity = 10 billion years. Gravitational contraction provided the energy that heated the core as the sun was forming. Contraction stopped when fusion began (10 million k) Gravitational equilibrium: energy provided by fusion maintains the pressure. Gravity is pushing in and fusion explosions are pushing out. Made almost entirely of h/he gas (plasma) Converts 4 billion kg of mass into energy each second. Solar wind: a flow of charged particles from the surface of the sun. Corona: outermost layer of solar atmosphere- 1 million k. Chromosphere: middle layer of solar atmosphere- 10^4 to 10^5 k. Convection zone: energy transported upward by rising hot gas.