I think you’re asking how we can see far-away celestial bodies without anything blocking our view:
Space is really empty. Even in our solar system we can see every planet without another getting in the way (the only reason we can’t sometimes is because of the sun). Even the moon is way farther away than it seems.
Space is very, very large and very, very, very empty. There is literally nothing out there at all, to several significant digits. Stars and planets occupy a terribly small fraction of the space in the visible universe. If there is something in the way, like a dust cloud, we can’t see the planet/star. But space is so empty that this seldom happens.
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