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Seeing stars during the daytime

  1. Oct 27, 2014 #1
    Is it possible to built a camera which filters blue light of the sky at the day, so that the stars can be visible?
     
  2. jcsd
  3. Oct 27, 2014 #2

    Drakkith

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    You can block the blue light, but there's still a lot of light coming through in the other wavelengths, so you still wouldn't be able to see stars. Remember that although blue light is scattered the most, the atmosphere scatters a portion of all incident light.
     
  4. Oct 27, 2014 #3
    Actually it is pretty easy to view or photograph the brighter planets and stars during the daytime. A filter that blocks blue wavelengths helps the contrast a bit but is not necessary.

    The hard part is to locate them. Really good manual setting circles or pre-aligned digital circles are almost a must. The usual disclaimers of using optics during daytime applies, i.e. only do it if you know what you are doing...
     
  5. Oct 27, 2014 #4

    Drakkith

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    Interesting. I knew that you could see several of the planets during the day if you knew where to look, but not the stars.
     
  6. Oct 27, 2014 #5

    mfb

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    Well, the stars are nearly point-like, while the sky delivers a constant* power per solid angle. If your resolution is good enough, the stars will be brighter than the area around them.

    *approximately, and assuming you don't try to find stars directly next to the sun
     
  7. Oct 29, 2014 #6
    During the daylight, stars are visible still better if telescope is used.

    But anyway, how it is possible to see stars, if blue light is filtered. At every point we have light from a star a light from the blue sky. Distribution of sum of frequencies gives two peaks. Let us imagine that chip of camera ignore the peak from the sky as much as possible. How the figure would look like? Maybe someone studied these peaks?

    Let us speculate that some birds have this filtration. Maybe they orient by stars by the day.
     
  8. Oct 30, 2014 #7

    Ken G

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    There's a sci fi story for you-- imagine a planet in perpetual daylight, with no other planets or moons visible, but with high-resolution cameras comes the serendipitous discovery of stars. What a momentous scientific discovery that would be!
     
  9. Oct 30, 2014 #8
    I'm not sure whether anyone can see a star on a bright day with their naked-eye, but you certainly can through an optical device.

    Even through a thick cloud cover, you can probably see the moon or even Jupiter with a 12" scope at night.
     
  10. Oct 30, 2014 #9

    Nugatory

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    It's been done. "Nightfall", by Isaac Asimov.
     
  11. Oct 30, 2014 #10

    anorlunda

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    You must be talking about Isaac Asimov's famous 1941 story Nightfall.
     
  12. Oct 30, 2014 #11

    davenn

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    wow
    that's one of Asimov's books I haven't read

    the only "star" I have seen during the day is Sirius, the only planet Venus

    D
     
  13. Oct 30, 2014 #12

    Ken G

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    Nightfall is a little different, because all the stars are foisted onto everyone's consciousness all at once-- it's a bit like Adams' "Total Perspective Vortex", where we are forced to confront our tininess in the universe. I think if we just discovered one star, then another, then another, like if we were picking them out in the daytime, we'd have to reassess the size of our universe, but we could do it gradually, like a scientific revolution. It's a bit like the discovery that the Earth orbited the Sun, which quickly led to the conclusion that the stars were way farther away than we thought. We might be frightened, or even go mad, if we were forced to grasp the vastness of the universe in a visceral way all at once, whereas just realizing that the universe is way larger than we thought seems to cause a less violent reaction. I remember when I was first told how far the stars were-- that's a lot less troubling then never having seen a night sky.
     
  14. Oct 30, 2014 #13
    Seeing stars and planets during the day was discovered thousands of years ago.

    It was noticed first when digging deep water wells... from the bottom of a deep well the diggers saw stars in the day time. A very "deep" discovery. :)

    The principle was applied in the construction of some early pyramids... One face of the pyramid had a vertical slot a few inches wide splitting the whole structure back down to the observer positioned in a chamber well back within and deep under the structure, able to watch the apparent passage of stars and planets as the pyramid rotated under the sky with the Earth's rotation, watching sky objects apparently pass across the slot, which subtended about 90 vertical degrees of the sky... using candle clocks or water clocks, the timing of these passages were recorded and charts drawn (aligning a local curved rule featuring graduate marks like a protractor against the distant slot for reference), so solar and lunar positions tracked, planet movements tracked, stars mapped, etc. These were basically astronomical observatories, cleverly aligned and designed, staffed by shifts of sophisticated fellows with keen eyesight, allowing 24 hour sky watching... a very long time ago.

    If you make a tube inner lined with black felt, and make the tube long enough, you can try this yourself... it basically absorbs almost all of the light that is not strictly parallel to the longitudinal axis of the tube, which favors the light from distance sources and reduces the light from scattered sources.
     
  15. Oct 30, 2014 #14
    That's really bizarre. I ought to look for Jupiter in the day one time.
     
  16. Nov 13, 2014 #15
    The higher the magnification the easier it is to see daylight stars, or it would be if the sky was very clear.
    A long tube and many baffels helps.
    Works in the same terrestrially for Antennae and binoculars
     
  17. Nov 14, 2014 #16

    Doug Huffman

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    http://www.livescience.com/34335-see-stars-daytime.html
     
  18. Nov 14, 2014 #17
    Somewhere I got the idea that angular resolution was involved, the star an infinitely narrow angle light source until atmosphere gets involved contributes more signal as the focal length is increased the sky contribution is reduced; as per signal to noise.
    .
     
  19. Nov 14, 2014 #18

    Ken G

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    Sure, you should be able to see stars by limiting the background-- you just need a narrow enough chimney. Probably all that link above does is show that a normal chimney is still not narrow enough, yet the principle is perfectly solid.
     
  20. Nov 15, 2014 #19

    mfb

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    The chimney alone won't help much. You need a better angular resolution, see my explanation in post 5.
     
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