Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Starry night

  1. Jun 29, 2005 #1
    The stars in the sky are all emitting their own light. The light is reflected for infinitely many times and part of the light energy will be stored in objects. But why is the sky so dark? Why is it not bright?
     
  2. jcsd
  3. Jun 29, 2005 #2

    Danger

    User Avatar
    Gold Member

    You appear to be a poet by nature, as opposed to a scientist. Light energy is unfortunately not 'stored' in objects. It is either absorbed or refracted (up to the point of being reflected).
     
  4. Jun 29, 2005 #3
    Can you see a light bulb from a mile away? How about 100000000000000000000000000000000000 miles?
     
  5. Jun 29, 2005 #4

    brewnog

    User Avatar
    Science Advisor
    Gold Member

    The sky is dark because it is empty, and there is nothing for the light to reflect off.
     
  6. Jun 29, 2005 #5

    SGT

    User Avatar

    I think lwymarie refers to Olbers paradox.
     
  7. Jun 29, 2005 #6

    krab

    User Avatar
    Science Advisor

    Excellent question, first asked by Kepler 400 years ago! Look up SGT's link.
     
  8. Jun 29, 2005 #7
    The sky isn't all bright because, for whatever reason, the more distant a light source the more red shifted is its light. When we check low enought frequencies, we even find the light shifted into the radio frequencies.
     
  9. Jun 30, 2005 #8
    Yes yes I was referring to the Olbers' Paradox. However I do not remember the details so I describe what I still remember about the paradox and see if some goodies can explain to me ;)
    Thx a lot =]
     
  10. Jun 30, 2005 #9

    Danger

    User Avatar
    Gold Member

    Olbers' paradox is based upon the false impression of an infinite universe. It supposes that everything has always existed. If such were true, then the sky would be uniformly bright. No matter in which way you look, there would be a star. The Big Bang eliminates that concept, because you can only look as far in space as you can look back in time. The 45 billion years or so that has elapsed since then is not long enough for sufficient star formation to cause infinite light creation. Moreover, the total energy content of the universe precludes the possibility of it ever happening.
     
  11. Jun 30, 2005 #10

    DaveC426913

    User Avatar
    Gold Member

    ??? 45 billion? Did I miss an issue of Sci Am? 13 billion at last count.
     
  12. Jun 30, 2005 #11

    Danger

    User Avatar
    Gold Member

    :redface: I usually proof-read these things better, but I was flat-out exhausted when I wrote that. It was supposed to say 15, which is a based upon one study that suggested that it might be as old as 20 billion years. Sorry, and thanks for catching it.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Starry night
  1. Bath night (Replies: 1)

  2. Night vision (Replies: 4)

  3. Light at night (Replies: 1)

Loading...