Why is Space Black?

by Tega Jessa on October 15, 2010

Why is Space Black

Saturn's rings contrast with the blackness of space. Credit: NASA/JPL/Space Science Institute

You might wonder with all the stars shining, why is space black? The answer is that in space, sunlight or any kind of star light does not have anything from which to bounce off. We see color because light is reflected back to our eyes. Normally if an object can reflect back all light we see the color white. However when we see the different colors we know about it is because only one part of the visible spectrum of light is reflected back to our eyes and the rest is absorbed by the object we are absorbing.

On Earth this phenomenon is why the sky is blue and clouds are white. Each have their unique color because of how light is scattered and reflected by molecules in the air. This does not happen in space. Since space is a perfect vacuum the only thing that can travel through it without a medium is light. Light natural follows a strait path so if it is not reflected by objects like planets and natural satellites it simply “absorbed” by space. However, in this case absorbed means it is not reflected to our eyes.

This also explains why we can see nebulae which should be simply clumps of invisible gas in space. We can’t see the air in front of us, right? The reason for this is that in nebulae and galaxies the gases and dust do reflect the light of the stars near them. So this makes it possible for us to seem them. However if were to enter a nebula the gases would not be as visible as from far off.

In the end, space is black to our perception because there are few molecules of matter that can reflect or scatter light like our atmosphere on Earth. Since light goes in a straight line it seems to be absorbed by the void and vacuum of space. Otherwise space would look similar to the sky on Earth.

We have written many articles about space for Universe Today. Here’s an article about how far is space, and here’s an article about deep space.

If you’d like to know anything about space, the best place to look is NASA’s Official Homepage. I also recommend you check out the website for the Hubble Space Telescope.

We’ve recorded many episodes of Astronomy Cast, including one about Hubble. Check it out, Episode 88: The Hubble Space Telescope.

Source: NASA

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