The lengthening of wavelengths of light emanating from objects moving away from an observer is called:*1 pointResonancePhase shiftsThe Doppler effectAcoustics

Break Down the Problem

1. Identify the core concept of the problem: the phenomenon related to wavelengths of light.
2. Assess the provided options for their relevance to light and motion.

Relevant Concepts

1. The phenomenon of light wavelengths change due to relative motion is commonly known as the Doppler effect.
2. Other options (resonance, phase shifts, acoustics) do not pertain to the specific change in wavelength due to motion.

Analysis and Detail

1. Doppler Effect: This effect describes how the frequency (and therefore the wavelength) of light changes depending on whether the source is moving toward or away from an observer. If the object is moving away, the observed wavelengths are stretched (redshift).
2. Resonance: In physics, resonance refers to the phenomenon where a system vibrates at a higher amplitude at specific frequencies, not related to the changing wavelength of light from moving objects.
3. Phase Shifts: This term generally denotes a change in phase of sinusoidal functions and isn't used for explaining changes in light wavelengths from motion.
4. Acoustics: This refers to the science of sound and its transmission, which isn’t relevant to the light wavelength changes in this context.

Verify and Summarize

After weighing the definitions and contexts of each term, it's evident that the Doppler effect is the only applicable term that describes how wavelengths of light lengthen when the source is moving away from an observer.

Final Answer

The lengthening of wavelengths of light emanating from objects moving away from an observer is called The Doppler effect.