if there are billions of stars in the universe that all send light our way how come the night sky is black?

Billions though there may be, they are tiny flecks of light compared with the vastness of empty space by which they are surrounded. In the overall scheme of things, the stars are just tiny flecks of dust, scattered very far apart in an empty void that absorbs fully the tiny amount of light that is produced.

It's really dark out there!

If the speed of light were infinite (so you could see everything as it is "now"), the night sky would not look very different to your eyes or to a small telescope. Essentially all of the naked-eye stars are a few thousand lightyears away at most, and stars generally live for tens of millions to many billions of years, and so they don't change much in a few thousand years. The motions of stars are all sub-relativistic, so stars do not move much in angle across the sky during the time the light is traveling to your eyes. This is not true, however, of the galaxies that can be seen through large telescopes. Some of them are billions of lightyears away, and they will have changed a lot between the time the light was emitted and "now".

I have to disagree with the answers so far! I'm amazed that a guy claiming to have a PhD in astrophysics can have written such a wrong answer!

In simple terms, there are so many stars (or galaxies, or galactic clusters...) that if we look in any direction we will be looking directly at one. Therefore light will be entering our eyes and in that direction the sky will appear bright. But it doesn't...

This is an ancient conundrum, recognised as long ago as the seventeenth century by Kepler; it is now known as Olbers' Paradox, after the German scientist Heinrich Wilhelm Olbers who wrote about it in 1863.

The short answer, generally accepted by astrophysicists, is that the universe is finite; so there is a limit to the number of stars (galaxies, clusters, etc.). The universe is also only so old; so since light takes time to travel, there hasn't been enough time for the light from the furthest star to reach us yet. Then, added to that the current model of the universe says that the further a star is away from us, the faster it is moving away from us - and a light source moving away has its light shifted into the red (longer wavelenght) part of the spectrum. A source that is moving fast enough will emit all its light at wavelengths too long for our eyes to register them.

This is discussed in several academic sites, a good source is NASA who give the following summary of the explanation:

"So, now on to the harder part - if the Universe is full of stars, why doesn't the light from all of them add up to make the whole sky bright all the time? It turns out that if the Universe was infinitely large and infinitely old, then we would expect the night sky to be bright from the light of all those stars. Every direction you looked in space you would be looking at a star. Yet we know from experience that space is black! This paradox is known as Olbers' Paradox. It is a paradox

because of the apparent contradiction between our expectation that the night sky be bright and our experience that it is black.

Many different explanations have been put forward to resolve Olbers' Paradox. The best solution at present is that the Universe is not infinitely old; it is somewhere around 15 billion years old. That means we can only see objects as far away as the distance light can travel in 15 billion years. The light from stars farther away than that has not yet had time to reach us and so can't contribute to making the sky bright.

Another reason that the sky may not be bright with the visible light of all the stars is because when a source of light is moving away from you, the wavelength of that light is made longer (which for light means more red.) This means that the light from stars that are moving away from us will become shifted towards red, and may shift so far that it is no longer visible at all. (Note: You hear the same effect when an ambulance passes you, and the pitch of the siren gets lower as the ambulance travels away from you; this effect is called the Doppler Effect)."

Because the sun is 96 000 000 miles away its extremely bright, even though its a tiny star.

The next nearest star is Proxima Centauri. Its about

5 879 000 000 000 miles away (more then 1000 times the distance and about 4.5 lightyears)

There are thousands of lightyears between stars and the light from those stars takes many thousands of years to get to Earth.

To put it into context, the light from the nearest star set out when the Iraq war started, the light from the furthest star in the galaxy set out about 80 000 years ago, before modern humans existed.

The light from the nearest galaxy, Andromeda, set out more then 2 million years ago.

There is so much space out there that its no wonder there is so much black space.

What I wonder is what space is actually made of. What is nothing? What effect does nothing have on matter and energy? Is space really nothing?

Because they are incredibly far apart, and the light from the far away stars spreads out so a very low intensity actually reaches us. Our atmosphere and to a lesser extent, the few molecules floating around in the millions of miles of space between us and those stars, also attenuate the light further. Even with that, there's probably a lot of light reaching us from stars that isn't intense enough or right wavelength for a human eye to pick out.

Part of the reason is that light intensity follows the inverse square law, which means that if a light source is twice as far away, it appears to be only one-fourth as bright. Since the stars are so incredibly distant, they look very dim.

They are all to far. The closest star system (excluding the sun) is the Alpha Centuri system with three stars that are approximately 25.8 trillion miles away from us. It takes the sun (which is millions of miles away) about 8 minutes to give us light and heat. Alpha Centuri is trillions of miles away so it takes much much longer and it is so far away it seems to us to be a small speck on the vast canvas of space.

This is Oblers' Paradox. Below is a link that discusses the current accepted theory as to why this is the case. In a nut shell it's due to the fact the the Universe is expanding.

They are so far apart, and space is so vast, that they seem faint. Another reason, is that there is lots of dust, asteroids, dark/black matter, planets, etc between us and these stars that the light is blocked, absorbed, reflected, and refracted away from us.

well there so far away and spread so the light they send out is so spread out that you only can see a bright spot in the sky, and there is not enough light reaching us for them to light anythink up as much so we could see.