• Question: You know the the way the sun is in space?how come space is dark?surely earth should be dark since the sun is miles and miles away and shouldn't space be bright because the sun and stars are their to light it?

    Asked by mazzy to Enda, Jean, Kate, Kev, Tim on 21 Nov 2012.
    • Photo: Jean Bourke

      Jean Bourke answered on 21 Nov 2012:

      Darkness is the absence of light. We see things because of the light waves reflected off them:that’s why you need to turn on the light to see stuff.

      We can’t actually see light, we see light when it bounces off something. You can’t actually see a laserbeam like in movies as there isn’t much for it to bounce off in the air. If you want to “see” the laser beam you need to use some smoke or powder blown into the air. When you do that you see the laser beam hitting off the particle of smoke, not the beam itself, this allows you to see the path of the beam. You can try this yourself with a laser pointer.

      Space is not completely dark but there can be very little light where there is nothing to give light and nothing for light to hit off (or at least it looks like there is no light to us). Stars emit light and planets reflect it (that’s why we can see them in the night sky). The stars we see at night are really far away and their light has travelled through the seemingly empty space to get to us. The areas between galaxies seem the darkest even though there might be loads of light there coz there is nothing for the light to bounce off allowing us to see it.

    • Photo: Tim Downing

      Tim Downing answered on 21 Nov 2012:

      Hi Mazzy – nice chat about this earlier!

      About half of the Earth is dark because the sun light cannot reach it as Jean described (unless it could bounce off other planets, like the moon?). The distances between the Earth and the Sun are huge at 93 million miles. So if you imagine all of Earth was compressed into a tiny piece of popcorn (before cooking!) then the Sun (the size of a mini-football) would be about 26 yards away from it. That’s nearly the same length as a double decker bus (maybe 90%).

      Then to consider how vast and empty space is, Jupiter (a tennis ball) is ~8 further double decker buses away, Saturn (a table tennis ball) is 9 more away, and Neptune at the edge of the solar system is another 9 buses away. So the sunlight has to travel a long way and with so much empty space without another to bounce off, this will appear dark.


    • Photo: Enda O'Connell

      Enda O'Connell answered on 21 Nov 2012:

      Hi Mazzy,

      Good chatting to you earlier. You asked a follow on question about the colour of Nothing and I said I’d get back to you on it if you used the Ask button.

      An area of space where there is no matter is called a vacuum, but there are no perfect vacuums, as you will find a few atoms of hydrogen floating around, even in deep space. We can create partial vacuums, where most matter is removed, and you’ll find these in your own home if you have light bulbs or a flask for your tea. But even if you were able to remove all matter you wouldn’t be able to remove gravity from acting on the area of space.

      So technically, there is no such thing as nothing.