Why do we have a night sky?

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Just saw a video of the hubble telescope zooming into a small patch of seemingly empty night sky revealing millions of stars and galaxies invisible to the naked eye.

Makes me wonder, if space is mostly empty and there’s possibly infinite number of stars and galaxies in any given part of the night sky, shouldn’t the night be as bright as the day?

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The universe is expanding. A consequence of this is that light from distant objects “shifts” into wavelengths that we can’t see.

Stars are really far, so far that even stray atoms and space dust scattered in mostly empty space dim their light eventually. All the stars that you see with naked eye as single stars are closer than 10000 lightyears or so.

Light becomes exponentially more dim the further away you are, following the ‘inverse square law’

ELI5: your voice gets quieter the further away you stand from me. Stars get dimmer the further away you stand from them! If you had really really big ears you could hear me louder. Telescopes have really really big eyes and they can see stars from further away!

If the universe is infinite, static and eternal we should see a star at every point in the sky. Yet there are definitely some dark spots.

The resolution is that the universe isn’t eternal nor static and the infinite part is well we don’t know but the true size here is irrelevant.

Since we know the universe started from a small dense point (according to general relativity exactly one singular point) it’s not eternal which because light requires time to get to places puts a limit to the furthest most point from which light can reach you. So the visible or observable universe has a finite volume. And so it contains a finite amount of matter so things that can emmit light. So not every point on the sky has to have a star on it.

Ok so whats up with using a telescope to see stars and other structures that otherwise aren’t visible.

There are two things, luminosity and wavelength.