Causes the wavelength of light from a star to either compress or stretch l

The reason is that the universe is expanding,  it is compressed because the space is expanding, the waves are being stretched out.

Explanation:

wavelength, distance between comparing purposes of two sequential waves. "Comparing focuses" alludes to two focuses or particles in a similar stage i.e., focuses that have finished indistinguishable divisions of their occasional movement. As a rule, in cross over (waves with guides wavering at right points toward the course of their development), frequency is estimated from peak to peak or from box to box; in longitudinal (waves with focuses vibrating a similar way as their development), it is estimated from pressure to pressure or from rarefaction to rarefaction.

The "wavelength compression" has a probability to produce cultivating signal at the nano-meter frequency by crushing optical frequency of the noticeable laser bar on a high energy electron pillar.

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explanation: