Question

The lengthening of a transmitted signal's wavelength and/or a decrease in its frequency, which indicates that the object is moving away from the observer, is called the

Answer 1

its called the red shift

Answer 2

That would be called the Doppler Effect.

The Doppler effect is the change in the frequency and/or wavelength relative to the movement of the source of the wave You would notice this effect when you hear sirens. As they move away there is a sudden change in pitch. This was named after the physicist who noticed this phenomenon, Christian Doppler.