How do we know things about quasars

[owlofcreamcheese]

This question applys to quasars and pulsars and all the other stuff we have discovered in space, honestly it applys to stars as well, but somehow it seems diffrent (mabey because we DO have a local example) my question is: how do we know anything about quasars?

what was the base assumption that allows us to determine the size or brightness? or the distance? it seems like you have to know something about them in advance to determine anything about them.

like say we found a new object in space called a blurch... we looked at it, how would we decide that it was a million miles across and a billion miles away, and not 1 mile across and 50 miles away. (well thats exageration, at that point paralax would tell us pretty quick).

same with red shift and dopler effect, what is the base assumption, if we took the blurch and saw the light was tinted red, what did we originally know how red it 'should be'.

what are the base assumptions we use when we discover a totally unknown object? it seems like alot of what we use is relitive to some other property of the object, we find size by knowing distance, we know speed by observeing color. something farther away looks smaller, something closer looks bigger, don't we have to know the size to find the distance or the distance to find the size?

and after a certain distance, we can't use paralax to see how fast it moves relitive to something else, I mean the stars haven't moved in my lifetime any nodiceable amount relitive to the earth.

I don't really understand, how do we find out ANYTHING about the objects we see in telescopes?