What is the DOPPLER EFFECT?

Doppler and Sound  When sound waves are made they spread out evenly in all directions like ripples on a pool of water  A stationary train sounds the same from all directions.

 When the train making the sound or the listener are moving there is an apparent change in frequency.  Higher frequency when moving towards each other.  Lower frequency when moving apart.

Doppler and Light  The Doppler effect occurs with light waves and other energy wave types.  In the area of astronomy the Doppler effect helps explain the red shift in stellar objects.

Red Shift  Stars emit light in specific patterns called spectral lines.  Stellar objects found outside of our galaxy all had spectral lines that had shifted towards the red end of the spectrum.

 Red light has lower wave frequency which means the objects are moving away from the earth.

Big Bang  The red shift shows every galaxy is moving away from the Earth.  This supports the concept of an expanding universe. This in turn supports the Big Bang theory.

Links  webphysics.davidson.edu/Applets/Doppler/Doppler.html lectureonline.cl.msu.edu/~mmp/applist/doppler/d.htm