In order for the speed of light relative to the moving observer to remain constant, the motion of the observer should cause a wavelength shift inversely proportional to the frequency shift. This is too preposterous so no one has the courage to teach it.
Professors almost universally deduce the frequency shift from a speed-of-light shift, but this speed-of-light shift remains implicit and carefully camouflaged. Here is Brian Greene as an example:
The Relativistic Doppler Effect—Video
https://www.youtube.com/watch?v=MBuLTzj3CWA
Some professors don't care much about Divine Albert's Divine Theory and teach the truth explicitly:
Professor Sidney Redner
https://sites.santafe.edu/~redner/:
"The Doppler effect is the shift in frequency of a wave that occurs when the wave source, or the detector of the wave, is moving. Applications of the Doppler effect range from medical tests using ultrasound to radar detectors and astronomy (with
electromagnetic waves)...Moving Observer. Let's say you, the observer, now move toward the source with velocity Vo. You encounter more waves per unit time than you did before. Relative to you, the waves travel at a higher speed: V' = V+Vo. The frequency
of the waves you detect is higher, and is given by: f' = V'/λ = (V+Vo)/λ."
http://physics.bu.edu/~redner/211-sp06/class19/class19_doppler.html
Pentcho Valev
https://twitter.com/pentcho_valev
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