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I About light -- why when I look at a star I see rays around it?

  1. Mar 24, 2016 #1
    Hi! I'm not studying physics and what I know about light is mostly what I've read on the internet and what I've learn thinking and observing the nature.
    I come to realize that the space is full of light. When I look at the black space, I don't see light but I know that is light everywhere up there, I dont see it because there isn't anything that stands and blocks the light so that it can bounce and come to me, but it is there. My question is, why when I look at a star I see rays around it? it suposse that light must be something behind making contrast so that light is reflected. what is explanation and an photonic level?. (sorry for my grammar I'm speak Spanish).

    Thank you
     
  2. jcsd
  3. Mar 24, 2016 #2
    You see rays around a star because the light you see comes directly from the star without any obstacle in between and when it enters the earth's atmosphere it undergoes continuos refraction by the atmosphere's increasing density, when it reaches your eye you can see the star but atmospheric density is not constant so the light cannot reach you continuously ,instead it keeps on changing its position due to changing density of air at different junctions of atmosphere so you see the star twinkling the rays around it are just the scattering of light done by dust particles which are near your eye.
     
  4. Mar 25, 2016 #3

    Drakkith

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    The light is scattered by inconsistencies and aberrations in the atmosphere and your eye.
     
  5. Mar 25, 2016 #4

    jbriggs444

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  6. Mar 25, 2016 #5

    davenn

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    but he didn't indicate he was using a scope ... tho that thought crossed my mind

    @CollinsArg please clarify if you were using a Newtonian scope or directly looking at the stars with no optical help


    Dave
     
  7. Mar 25, 2016 #6

    HallsofIvy

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    This could also be the result of a slight astigmatism.
     
  8. Mar 25, 2016 #7
    Do you have astigmatism?
     
  9. Mar 25, 2016 #8
    Without scope. What I mean is, suppose that I'm looking at Jupiter, it looks like a bright big star, but Jupiter is a round planet, but I don't see the light round, I see it almost like the tipical symbol of a star.
     
  10. Mar 25, 2016 #9
    Nope, I don't
     
  11. Mar 25, 2016 #10

    jbriggs444

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    If you tilt your head while viewing Jupiter do the rays rotate with your head or stay fixed?
     
  12. Mar 25, 2016 #11
    All the planets (although just barley in the case of Venus at close approach) are smaller than the resolution of the eye and therefore appear point like. The most mundane effect of their larger angular diameter noticeable using the naked eye is that they tend to twinkle less than stars.
     
  13. Mar 25, 2016 #12

    davenn

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    stars and planets should look pinpoint to the naked eye, UNLESS you have an eye problem
    you shouldn't be seeing any spikes from the stars
     
  14. Mar 25, 2016 #13
    Mmm, that's weird: So you see stars like this?: north-star-companions.jpg


    What I see is most like this: Polaris.jpg
     
  15. Mar 25, 2016 #14
    nice, I'll try that!
     
  16. Mar 25, 2016 #15

    davenn

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    yes, I and I would suspect most people see stars as in the top pic

    The diffraction spikes you see in that bottom image are what you get when using (more accurately) photographing with a Newtonian telescope

    eg...

    newt spikes.jpg


    You don't get them with Cassegrain or Schmidt-Cassegrain telescopes because the secondary mirror doesn't have a spider to support it


    Dave
     
  17. Mar 26, 2016 #16

    sophiecentaur

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    I don't have 'Elf' vision but, when I look at Jupiter, it looks definitely like a disc. Likewise for Saturn - but only just. Mars definitely looks different enough to convince me it's also a disc. It's not just the 'un-star-like' appearance, I'm sure.
    Venus, of course, really does look like a little Moon and you can even see its phases.
     
  18. Mar 26, 2016 #17

    davenn

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    Naked eye ???

    Have never ever heard anyone else say they can make out discs of those planets naked eye


    Dave
     
  19. Mar 26, 2016 #18

    Vanadium 50

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    I wouldn't say I can see the disk of Venus, but I definitely see a difference in shape from its phases - it looks rounder or longer depending on time of year.
     
  20. Mar 26, 2016 #19
    My guess is that it's probably just a halo he's seeing around the planet when he looks at it in the night sky.

    Which is a sign he should think about vision screening, by the way.
     
  21. Mar 26, 2016 #20

    sophiecentaur

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    Last month I had a sight test for new specs and I could read the bottom line, as usual (with the new prescription, of course). The appearance of Jupiter is so strikingly different from the stars and the only quality that I can recognise is its Moon-like appearance. You can keep your Rayleigh Criterion and your Airey Discs (which are only rules of thumb). My subjective appreciation of those planets is that they are tiny discs. This, of course, could be because I have learned what they are but I could guarantee, if someone placed an equivalent image somewhere else, I would 'see' the same thing. Not keeping up with the published tables of ephemera or knowing the star maps I still see what I see and , when checking on the web, I am nearly always right. I try to be as objective as I can be. Could it just be the lack of twinkle? Perhaps.
     
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