Summary of physical laws for astronomy

Units of measurement.

Important numbers:

• Speed of light: 3 x 10⁸ m/s.
• Astronomical unit: 150 x 10⁶ km.
• Distance to center of the Galaxy: 25 kly.
• Distance to Andromeda Galaxy: 2 Mly.
• Age of the universe (from Hubble Law), roughly 10 x 10⁹ y.
• Temperature of Sun at photosphere: 6000 K.

Laws:

• Distance d an object goes if it moves for time t at speed v.
  
• Wavelength and frequency of light.
  
• Energy radiated by a blackbody per unit surface area per unit time
  
• Energy radiated by a whole star per unit time, given the radius and surface temperature of the star.
  
• Wavelength of peak intensity of blackbody radiation.
  
• Energy of a single photon
  
• Energy conservation
  
  
• Relation between luminosity of a star and its apparent brightness when viewed at a distance d from the star.
  
• Mass, gravity, and motion. The total mass of a two star system as determined from the size of the star's orbits (the semimajor axis a) in AU and the orbital period P in years.
  
• Distance and parallax. The distance to a star in pc as determined from its parallax angle in arc seconds.
  
• The Hubble Law relating distance and speed of recession of distant galaxies.