- If a light source is moving with respect to an observer
(or the other way around) strangely enough the Speed of
the light being emitted doesn't change but the Frequency
and Wavelength do.
- The waves get ``bunched up'' [higher , shorter ] in the
forward direction and ``stretched out'' [lower , longer = ] in the
- Everybody know this effect in sound waves. (Think about the train whistle
pitch as the train zooms past).
- The change in frequency is called the Doppler Shift
- is the ``at rest'' wavelength;
- is the apparent wavelength for the velocity v.
- v is the relative velocity between the source and observer and
- c is the speed of light.
Q. How fast would the judge calculate you were traveling?
- You are busy talking on your car phone and drive right through
a red light. In court you claim that the RED
light looked GREEN to you
because you where approaching the light and the radiation was
Doppler Shifted into the green part of the spectrum.
= 110,000,000 miles/hour
Thu Jan 15 13:12:09 PST 1998