How does the phenomenon of *redshift* manifest as light travels from a receding galaxy?

As light travels from a galaxy moving away, its wavelength is stretched toward the red end of the spectrum.

Redshift is the crucial observable signature used to infer cosmic expansion. It occurs because, as light travels across expanding space, the medium itself stretches the photons' wavelength during transit. Longer wavelengths correspond to the red end of the visible light spectrum. Therefore, the greater the observed redshift, the more the space between the distant galaxy and the observer has stretched, directly correlating with a faster speed of recession, as described by Hubble's Law. This stretching effect is distinct from the Doppler shift caused by motion through space, although the resulting spectral shift is mathematically analogous.