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Why do stars twinkle?

  1. Feb 24, 2004 #1
    why do stars twinkle??

    has it got anything to do with the photons emitted from the burning stars? i mean that is it because of the uneven frequency of photons reaching your retina that would cause u so register the lights in an irregular fashion, causing the star to 'twinkle'
    what about supernovas, would we be able to see something different from the normal shining lights from the stars if there's a supernova going on??
  2. jcsd
  3. Feb 24, 2004 #2
    Part of the twinkling is caused by sperical aberration. Spherical aberation is seperation of light into it's seperate colors by passing through a lens which directs the different colors to a focal line instead of a focal point, with each color focusing at a different point along the line. The atmosphere acts as the lens.
  4. Feb 24, 2004 #3
    Also, stars are actively creating light, unlike planets which merely reflect light. One of the ways of knowing if you are looking at a planet or a star is that planets don't twinkle (although they are still effected some by spherical aberration).
  5. Feb 24, 2004 #4


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    I always wondered about that! By the time light reaches your eye, what does it matter whether it was directly created by a star or happened to bounce off a planet on its way?

    What really happens is this: stars are so far away that at the greatest possible magnification, a star still looks like a "point" of light. The visible (to the naked eye) planets are close enough (compared to stars!) that even with only slight magnification, you see a "disk"- and, in fact, your naked eye sees a disk even though it may not be noticeable.

    A "ripple" in the sky (sudden temperature or pressure change that changes the refraction index slightly) completely disrupts the single point you see for a star but does not, in general, completely disrupt the small disk of a planet. That disruption is what we see as "twinkling" of stars.
  6. Feb 24, 2004 #5

    the reason it appears to have lines around it when you look through a telescope is that the lens in the telescope have to be attached by something that blocks some of the light causing the picture to appear in the end to be sparkiling. I believe they are called spider veins. Also you can tell when you are looking at a star versus say a galaxy because a star will have that effect but a galaxy won't.
  7. Feb 24, 2004 #6


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    In short, the atmosphere is a mess. It is full of pockets of hot and cold air, and since cold air is more dense, light travels "slower" in it, producing all sorts of unpredictable refraction effects. This usually outweighs whatever interstellar obstacles it comes across.

    Retina cells are triggered by a minimum of 6 photons, IIRC...
  8. Feb 24, 2004 #7
    Re: Telescope

    Yes. Spider vanes hold the secondary mirrors in some reflecting telescopes (in some types it is attached to optical glass or a lens). The thickness and configuration of these vanes (some are curved some are straight) distorts the image breaking the airy disk (the out of focus view of a star) into segments related to the number and arrangement of the arms. For the most part they have only a minimal effect if the mirrors are good quality and thin spider arms are employed. Personally I use just one (or two one right behind the other) when I build reflecting scopes. I barely notice the distortion.

    The inability of a lens to focus all the colors to a single point has a greater effect in refractor scopes often causing coma (a colored glowing haze) to appear to surround bright objects, especially when you try and magnify them too much.
  9. Feb 24, 2004 #8
    "Twinkling" is also known to astronomers as "seeing." Some observatories employ telescopes with flexible mirrors that correct for this aberration by responding to feedback from a laser beam parallel to the line of sight. The beam is distorted by seeing, and its affected signal is immediately compensated for by the mirror, reducing the telescope's resolution some ten fold. One must be careful not to blind pilots of passing planes with this substantial laser!
  10. Feb 24, 2004 #9


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    Obstructions like spider vanes do not cause twinkling. They cause diffraction spikes. The atmosphere causes twinkling.

    - Warren
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