ASTR 20 Lecture Notes - Lecture 25: Annie Jump Cannon, Stellar Classification, Inverse-Square Law
Document Summary
The number of sunspots rises and fall in 11-year cycles. The sunspot cycle has something to do with the winding and twisting of the sun"s magnetic field. The stretching and twisting of magnetic field lines near the sun"s surface causes solar activity. Brightness of a star depends on both distance and luminosity. Amount of energy a star radiates every second (energy per second=watts) (apparent) brightness: the amount of starlight that reaches earth (energy per second per square meter) Luminosity passing through each sphere is the same. Divide luminosity by area of sphere to get brightness-inverse square law. Apparent positions of the nearest stars shift by about an arc second as earth orbits the sun. If we measure a star"s apparent brightness and distance, we can compute its luminosity with the inverse square law for light. Parallax tells us distances to the nearest stars. Level of ionization also reveals a star"s temperature.
