Moving Targets

  • By David Colarusso
  • Posted 11.11.00
  • NOVA

Ever notice how the pitch of an ambulance's siren changes as it speeds by? If so, then you're already familiar with a phenomenon that astronomers use to measure the relative speeds of astronomical objects. It's called the Doppler effect, and astronomers use it, together with careful observations of the light from stars, to figure out how fast the stars are moving towards or away from Earth. Try it yourself in this activity.

Launch Interactive Printable Version

See how astronomers use the Doppler effect and redshift to determine the speed and direction of stellar objects.

This feature originally appeared on the site for the NOVA program Runaway Universe.

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