There was an idea some time ago that if there is an infinite number of stars, then we should look out on a totally bright sky all the time, since the light doesn’t ‘wear out’ as it travels towards us. So there must be gaps or things absorbing the light – I think there is this stuff ‘dark matter’ which hoovers up light which we don’t really know what it is…
The only things that are visible to us are things that reflect or scatter light. So space (the bit between the planets, stars etc) is dark because it is empty – there is nothing for light to bounce off.
There could be some mistakes in all this, so I’d be interested to read what the other’s say. But I’ll have a go.
Space is more or less empty (with some dust that sometimes blocks light from distant stars)
There are big gaps between the stars and they are getting bigger.
Light from stars very far away hasn’t had time to reach us yet.
Only a small proportion of the light from a star reaches us (because most is going off in all the other possible directions) – so the further away you are from a star the less light reaches you (I think).
So there is an absence of light coming from some directions (where the stars are too far away or behind dust), and that’s why (I think) most of the night sky looks dark (i.e. why there are gaps between the stars).
I also think it’s quite bright in space in the sense that the sun (if you are anywhere near it) is not passing through the atmosphere and is much more intense than it appear on Earth.
We only see things if they reflect or scatter light from a source (eg the Sun) which then enters our eyes. Space (the bits between the planets, stars and galaxies) is dark because it is pretty much a vacuum – it contains very little and there is nothing for light to bounce off.