Measuring the Characteristics of Stars

Characteristic Technique
Surface temperature Determine the colour (very rough)
Measure the spectrum and get the spectral type
Chemical composition Determine which lines are present in the spectrum
Luminosity Measure the apparent brightness and compensate for distance
Radial velocity Measure the Doppler shift in the spectrum
Rotation Measure the width of spectral lines
Mass Measure the period and radial velocity curves of spectroscopic binary stars
Diameter Measure the way a star's light is blocked by the Moon
Measure the light curves and Doppler shifts for eclipsing binary stars

Measuring Distance from Earth

  1. Parallax
  2. Using brightness measurements
    • Look at the star, determine it's color spectrum (good indication of it's actual brightness)
    • Compare the actual brightness with the apparent brightness, they can determine the distance
      • It's apparent brightness will be dimmer
  3. Using an H-R diagram
    1. Observe distant star's apparent magnitude and spectral type
    2. Spectrum gives luminosity class
    3. Spectral class and luminosity class gives a brightness independent of distance
    4. Distance-magnitude relationship gives you distance



Types of Stars

Colour and Temperature

Star Colour Approximate Temperature
Blue 25,000 K
White 10,000 K
Yellow 6000 K
Orange 4000 K
Red 3000 K

Space Astronomy