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Possibilities of Rainbows

  1. Mar 12, 2015 #1
    I think this is the correct subforum for this question. If I'm wrong, please, forgive me.

    Well, to the question.

    I was browsing some wonderful pictures and videos and one crossed my vision and raised a doubt.

    When I studied optics back in my school, I learned that the red wave stayed in the "outside" part of the rainbow, in the "outside" curvature. Also, I never saw a rainbow so close to the ground.
    Is this possible or it's probably graphical working?

    Many thanks for the attention.
    Best wishes.
  2. jcsd
  3. Mar 12, 2015 #2

    Suraj M

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    see the secondary rainbow, you'll understand the formation of what you saw.
    Then it's your first, don't make it your last :)
  4. Mar 12, 2015 #3


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    What makes you think this is a rainbow? It could easily be a refraction off a glass or window.

  5. Mar 12, 2015 #4
    Because it was from a video and it was outdoors and the people were seeing the rainbow and all.

    I've seen this many months ago, so I don't have the page anymore, sorry. I just kept this image from the video.
  6. Mar 12, 2015 #5


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    Rainbows seen so close to the ground are rare simply because of the geometry required.

    The droplet-laden air must be the right angular distance from the sun (~40 degrees for primary bow, 50 degrees for secondary bow with inverted colours). In order for that to occur below the horizon line, the air must be pretty much at your feet.

    This occurs when looking through a sprinkler or other misting apparatus, but rarely occurs in nature because you're usually looking at a volume of air in the distance and in the sky.

    Last edited by a moderator: Mar 13, 2015
  7. Mar 12, 2015 #6


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    Rainbows are formed with the sun behind the observer and not in front, as that diagram implies. (I wonder where it came from originally as there are hundreds of the correct version if you look on google) There are only a few situations where the Sun is low enough in the sky and the observer high enough to see the invert of the circular bow. I have had spectacular views from an aeroplane of a complete circle and a few good ones in the back garden with a garden hose, getting just the correct angles.

    You can get coloured halos around the sun - typically die to ice crystals in the atmosphere.
  8. Mar 12, 2015 #7
    I think this video was filmed in Tibet, which would explain the angle.
  9. Mar 13, 2015 #8


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    Quite possibly; looking down into a valley with the Sun quite low in the sky.
    You can see, from the lighting on the leaves, that the Sun is actually behind the camera.
  10. Mar 13, 2015 #9
    Can secondary rainbows appear alone?
  11. Mar 13, 2015 #10

    Suraj M

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    i don't see why not!If the sun is at 51° from the water droplets.
  12. Mar 13, 2015 #11


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    Yes, in theory.

    Rainbows require the presence of droplet-laden air in the right place. If there is droplet-laden air 50 degrees away from the sun, but not 40 degrees away from the sun, then the primary bow will not be seen.
  13. Mar 13, 2015 #12


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    The two rainbows have no direct relationship. Neither is caused by the other. They require a number things to appear:

    1. A bright, pointlike illumination source
    2. A path from that source to the refraction area.
    3. A volume of air at the refraction area containing suspended spherical droplets.
    4. A path from the refraction area to your eye.

    If there is a cloud in the way of the light illuminating the area responsible for the primary rainbow, you don't get the primary rainbow. If there are no droplets in the area responsible for the primary rainbow, you don't get the primary rainbow. If you hold your hand in front of your eye so that you can't see the primary rainbow, you won't see the primary rainbow. In all three cases you may nonetheless be able to see the secondary rainbow.
  14. Mar 14, 2015 #13
    I found another video of the same rainbow. Turns out that this rainbow was considered a holy sign because it appeared during the funeral of one tibetan Lama

    Here it is.

    It's weird, but I don't think it's impossible.
  15. Mar 14, 2015 #14


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    No, that is very weird. (Assuming no tampering.)

    A secondary bow occurring without a primary isn't hard to do over a short arc, because the pocket of droplet-laden air can be arbitrarily small, or in the wrong place, so only the secondary is formed. But - it forms only in a short arc. [see middle panel in highly technically-accurate simulation below]

    But the secondary bow in the video is pretty much fully circular. How can you have a mass of droplet-laden air in a circle 50 degrees from the sun but not at 40 degrees? What? Is it a torus of moist air?

    That makes no sense, so there must be another explanation.


    One thing I should point out in the video that I did not simulate: you can see that the bow is visible in front of spectators very nearby, which means the moisture-laden air is not distant and high-in-the-sky; the videographer is in the air mass.
    Last edited: Mar 14, 2015
  16. Mar 14, 2015 #15


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    Looking around the webernets, I see that it is not uncommon afterall.

    Googling full circle rainbow, I can find pics of "normal" full circle double rainbows, but also full circle inverted-only rainbows (characterized by having the blue band outside, and red inside).


    So I think this is more closely-related to halos or ice-bows, which are due to ice crystals, rather than water-droplets.
    Also, they occur at 22 degrees, not at 40 or 50 degrees.

    I don't have a complete explanation for the different phenom yet, but I think we're getting closer.
  17. Mar 14, 2015 #16


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    How many crystals/droplets/whatever you think there are between the camera and the monk in the picture below?


    This looks like a effect created by the cameras optics, or something attached to the camera.
  18. Mar 14, 2015 #17


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    I know. It's a mystery.

    Possibly. I've seen a lot of camera optics effects, but not like this. Not saying I disagree, just that it's a mystery to me.[/QUOTE]
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