Explain why astronomers use the term “blueshifted” for objects moving toward us and “redshifted” for objects moving away from us.

As per the dopper's effect of light we know that the frequency of light will change due to relative motion of source and observer

it is given as

so here we know that

now if source is moving towards the observer then frequency received by the observer is more than the actual frequency

so here the apparent wavelength would be smaller

as we know that

so here if frequency is is ore than actual frequency then the wavelength would be smaller

so it is known as blueshift

Similarly if object is moving away from the observer then the frequency received will be less than the actual frequency

So here we can say that the wavelength would be more than the actual wavelength

So it is known as Redshift

wavelength variability is the right one

compass can be used day and night, cloudy or sunny