However, when the ambulance is moving ... Similarly, light wavelengths from an object emitting light are stretched by movement away from the observer. This is called the red shift.

It happens with any wave source that moves towards or away from an observer. If the object is moving ... red end of the spectrum, as you can see below: This is called red-shift. Light is shifted ...

Yet if the light source is moving away, the lines are shifted ... Slipher knew that a shift toward red suggested the body was moving rapidly away from the observer. But he had no way to measure ...