Planet shadow seen

• Recall “planets” discovered via radial velocity

  • Star and planet orbit about their common center of mass
    • demo with orbit apparatus
  • Can’t see planet (too dim), but can detect reflex motion of star
    • Newtons 3rd law, action = -reaction
  • star’s motion generates a Doppler shift
    • objects moving toward us blue-shifted (higher frequency)
    • objects moving away are red-shifted
  • Example 51 Peg
    • vu-graph of Doppler shifts
  • First planet found
  • Using Newton/Kepler’s laws we derived
    • a = 0.05 AU
    • planet mass = 0.4 times Jupiter’s
      • planet more massive if orbit not edge-on

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