How are we able to know how extremely far galaxies look like? Shouldn’t they be completely covered/invisible because of the huge amount of celestial bodies that are closer to us?

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After a certain distance, won’t all the celebrities bodies create some sort of wall where we can’t see further?

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Technically yes, but you underestimate how empty space is. There’s just not enough celestial bodies in the way to block the view.

Some spectrums of electromagnetic radiation, like infrared, x-rays, heat residue etc can normally pass through obscuring objects, and thus allowing us to observe what’s behind them.

Also, space isn’t that dense. Distances between things in space are extreme, so outside of some specific giant gas clouds we pretty much never reach a point in our observable universe where things are so packed together as to obscure another thing completely, and even if they are the effect of gravitational lensing still allows us to at least partially see what’s happening behind them.

No. Space is too empty, and the Universe is too small, for that to happen. Almost all lines of sight into space don’t encounter anything until they reach the [cosmic microwave background](https://en.wikipedia.org/wiki/CMBR), at a distance corresponding to a time about 370,000 years after the Big Bang. At that time, the Universe *was* dense enough that light couldn’t travel freely, so that’s where lines of sight end (at least if you’re looking at light, rather than things like gravitational waves).