How do we figure out properties of galaxies?

• Size:

• Measure angular size and use geometry:

  • R=D sin() (need to know the distance)

• Luminosity:

• Measure apparent brightness:

  • L=4D2 B (need to know the distance)

• Mass:

• Measure rotational velocity (using Doppler shift) and use Kepler’s Laws

  • M= v2 R/G = v2 D sin()/G (need to know the distance)

Notes: