Hi! I'm pretty much a pop science guy so I can't say I know much about the underlying math or physics, but after listening to these lectures about pretty much everything over and over again, there is one thing I just can't seem to find the answer to. The explanation of red/blue shift is pretty clear to me, however, how do we know the difference between the red shift from an object moving away from us and an object in rest emitting that same wavelength to begin with? If our only source of information from distant stars is light in an expanding universe, how do we know what they would look like at rest to begin with? Sorry if this is a dumb question, but I can't seem to find a good explanation. Thanks in advance!