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Stars we see are actually their past?

  1. Feb 11, 2016 #1
    One questions that im really confused with!
    If the sun is 8 light minutes away, this means that whenever we see the Sun, we are actually looking at how the Sun looked like 8 minutes ago if im not wrong.
    If we look at a star that is lets say 15 billion light years away from the earth, is it even possible for us to say that the star we see could have died because all we are seeing is the past? (how it looked like 15 billion years ago?)
    Im sorry if you think its a stupid question but im curious about it
     
  2. jcsd
  3. Feb 11, 2016 #2

    phinds

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    It's a perfectly reasonable question and one that I think comes to all of us when we first start finding out about this stuff. Yep, we're seeing them in the past and for all we know they are "now" long dead and gone. I put "now" in quotes because "now" for something 15 billion light years away is a non-trivial topic.

    And by the way, the universe is less that 15 billion years old, so your number is a bit too large.
     
  4. Feb 11, 2016 #3

    davenn

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    hi there

    welcome to PF :smile:

    yup, everything we look at out in space, we are seeing it in the past

    There was a new supernova ( an exploding star) discovered in a galaxy called Centaurus A ( NGC5128) just a few days ago
    it took around 12 million years for the light of that explosion to reach earth ..... ie. it happened 12 million years ago !!


    Dave
     
  5. Feb 11, 2016 #4

    phinds

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    @davenn I see you're a day late (and probably a dollar short) :smile:

    Well, OK, maybe only a few seconds late
     
  6. Feb 11, 2016 #5

    davenn

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    what are you referring to ??
     
  7. Feb 11, 2016 #6

    phinds

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    Just a smart-ass remark about the fact that I beat you to the reply by a few seconds. Come on, try to keep up here :smile:
     
  8. Feb 11, 2016 #7

    davenn

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    it took time to google NGC5128 to find its distance :wink::rolleyes:
     
  9. Feb 11, 2016 #8

    phinds

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    See, that's what you get for using facts in your answer instead of just making s*** up the way I do :smile:
     
  10. Feb 11, 2016 #9

    phinds

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    @Esas Shakeel, sorry Dave and I have hijacked your thread with our foolishness. PF is generally a serious science forum but occasionally a few of us get carried away.
     
  11. Feb 11, 2016 #10
    One thing that might interest you is that the oldest light we now can 'see' comes from a time when the Universe was much less than even 1 million years old.
    At this very early time no stars or galaxies had even formed yet.
    https://en.wikipedia.org/wiki/Cosmic_microwave_background
     
  12. Feb 11, 2016 #11
    Not only the light we see but also the gravity pulling on us is from the past. Because gravity propagates at the speed of light, if the sun suddenly vanished, the earth would continue orbiting where the sun was for another 8 minutes before flying off into space at a tangent.
     
  13. Feb 11, 2016 #12
    ...."all we are seeing is the past?"....

    Something we see a foot away from us is already about 1 nanosecond in the past. A mountain peak or volcanic plume 50 miles away is about...25 milliseconds in the past.

    c roughly 1 ft/nS
     
  14. Feb 11, 2016 #13
    Incredible response from you guys! Thanks alot! Everything makes much more sense now
    And @phinds haha, I dont mind, Its good to be carried away every once in a while I think :)
     
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