• Question: if theres light on earth by the sun why is space dark

    Asked by 426speq37 to Stephen on 4 Mar 2019.
    • Photo: Stephen O'Connor

      Stephen O'Connor answered on 4 Mar 2019: last edited 6 Mar 2019 5:45 pm

      Great question! First, some background. In 1929 a famous American astronomer called Edwin Hubble (who NASA named the Hubble Space Telescope after!!) was looking at very far away galaxies through his telescope and noticed that the light coming from them was red. In fact, the further away the galaxy was, the more red it looked. Red light has a longer wavelength than green light or blue light. Hubble concluded that the light from these distant galaxies was being stretched somehow as it travelled across the universe. Scientists realised that the Universe was EXPANDING! This has two important consequences that make space ‘dark’:

      1. The light that we see with our eyes is called visible light (red, green and blue light), so when we look at a star or galaxy with our own eyes we are seeing visible light. If it comes from very far away places it may have stretched into wavelengths that are too long for our eyes to detect.

      2. There is a universal limit to the speed that light can travel. Some stars and galaxies are SOOO far away from us that the speed at which space is expanding means that even light is not travelling fast enough to reach our eyes, so we can’t see them.

      Again this is a great question and shows you have a curious mind!

      Check out this link for more information: https://www.youtube.com/watch?v=YS18GPk1LYo

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