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Why do lights shine?

  1. Nov 30, 2014 #1
    I'm not sure this is the intended section for this question, but I couldn't find a better one, so here it goes: Why do lights shine?

    By this I mean, when you see a light, particularly in the dark, it seems to have lines/spikes extending out from it, outside the bounds of the source itself. Anyone know why this happens?
    I'm not really talking about the 'glow' around lights (unless it's the same effect), also I included a quick sketch to show what i'm talking about
    Edit: Not talking about with a camera, just when looking at it normally
     

    Attached Files:

  2. jcsd
  3. Nov 30, 2014 #2
    like this? The_sun1.jpg
    Color_image_of_galaxy_cluster_MCS_J0416.1–2403.jpg
    or the big red star on the lower right?

    Well either way I was wondering a while ago why that was never found a reason yet...
     
  4. Nov 30, 2014 #3

    jedishrfu

    Staff: Mentor

    In reflector telescopes the support struts interfere with the light received and act to defract it.

    http://en.m.wikipedia.org/wiki/Diffraction_spike

    Similarly, the particles in the eye do the same thing.

    http://en.allexperts.com/q/Ophthalmology-Optometry-979/2012/5/rays-light-radiating-light.htm [Broken]
     
    Last edited by a moderator: May 7, 2017
  5. Nov 30, 2014 #4

    davenn

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    Gold Member

    Telescopic views are a different issue
    you will see that in telescopes that have spider mounts for the secondary mirrors
    like Newtonian style scopes

    you can produce the same effect in a camera pic of streetlights by using a high aperture setting ... around f18 - f30

    visually ( eyes only) I would have thought it would have been caused primarily by dust, mist other aerosols in the air between the light and the eye

    lets see what others say :)
     
    Last edited: Nov 30, 2014
  6. Nov 30, 2014 #5

    Drakkith

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    Staff: Mentor

    Some people say that holding their eyelid open with their fingers, so that neither the eyelid nor the eyelashes are in the path of the oncoming light entering your pupil, the spikes go away. I could see part of this being caused by diffraction from eyelashes.

    I've also noticed that if my glasses are smudged slightly then I will sometimes get spikes.
     
  7. Nov 30, 2014 #6
    They are always aligned parallel and perpendicular to the Earth. 4 main spikes, nothing I can do makes them go away looking out the window at a streetlight right now I see it. The brighter the light appears the longer they are.
     
  8. Dec 1, 2014 #7

    davenn

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    closed window ? ie. through the glass ?

    if so ... open the window and try again and then consider the last sentence in Drakkith's last post
     
  9. Dec 1, 2014 #8
    I always see these! I've always had perfect vision (until recently, slightly far-sighted now), on a clear night free from light pollution looking at the stars in the sky the brighter the magnitude the longer and thicker at the source the spikes are. And as I mentioned in a previous post they stay oriented to the Earth regardless of turning my head. I remember at a very young age thinking they were caused by Earth's magnetic field but I have yet to find a satisfactory explanation.
     
  10. Dec 1, 2014 #9

    CWatters

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    When I lean my head they stay orientated to my head not the planet. In the case of bright lights I assumed this was diffraction spikes from eyelashes. Too cloudy here tonight to try with stars.
     
  11. Dec 1, 2014 #10
    I just thought about looking straight up and hopefully see some deviation that adds any insight on a clear night.
     
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