Comparison of Stars
  • Key parameters: Temperature, Size, Mass, Distance, Luminosity, Motion, Composition.
Spectral Classification
  • Early Work: Edward Pickering's team classified stellar spectra by color and Hydrogen lines.
  • Cannon's System: Annie Jump Cannon simplified to O, B, A, F, G, K, M, with 10 subdivisions (0-9).
  • Interpretation: Spectra identify temperature differences; Hydrogen absorption lines vary with temperature.
Measuring Distances
  • Parallax: d(pc)=1/p(")d(pc) = 1/p("). 1 parsec = 3.26 light-years. Stellar distances also measured by radar.
Brightness & Luminosity
  • Magnitude: Brightness measure (Hipparchus). A 5-magnitude difference is a 100-fold brightness factor.
  • Luminosity: Power output expressed as L=P2a3L = \frac{P^2}{a^3} (Stefan-Boltzmann Law). Luminosity classes indicate distance and composition.
Stellar Properties
  • Size: Determined by comparing luminosity: L=R2T4L = R^2 T^4.
  • Mass: For binary stars, calculated using Newton's Kepler's third law: M+m=P2a3M+m = \frac{P^2}{a^3}.
Hertzsprung-Russell (H-R) Diagram
  • Purpose: Shows the relationship between temperature, luminosity, and spectral classification.
  • Main Sequence: 90% of stars, with direct relationships between mass, luminosity, and radius.
  • Other Stars: Includes cool but bright, and faint but hot stars (giants and white dwarfs) not on the main sequence.