1. Mick West

    Mick West Administrator Staff Member

    A recent post on The Ann Arbor News Facebook Page displayed a photo of a solar halo with some other clouds and some aircraft contrails
    [​IMG]
    They included a short explanation of what it was:
    Unfortunately the comments below the photo were quickly overrun by believers in the "chemtrail" theory (and then by other people trying to explain things to them). A few samples:
    There's two equally important things you need to know about this story:

    1) Atmospheric Optical Phenomena such as Halos, Sun-Dogs, "Fire Rainbows", and iridescent clouds" have been seen for thousands of years, and recorded and understood for over a hundred years
    2) They can only be made by clouds of ice water.

    The Science and History of Halos, etc.

    Haloes have been observed since ancient times. Here's a 17th Century painting of some haloes.
    [​IMG]

    And here's a 1957 book showing a halo with some contrails contributing to it:
    [​IMG]
    https://www.flickr.com/photos/metabunk/sets/72157642384424663/

    Halos are formed by the refraction of sunlight through billions of tiny ice crystals in the air.

    The colors in the halo occur because of refraction. This the bending of light as it goes through a prism. Different wavelengths (colors) of light are bent
    different amounts, and this produces the spectrum of colors. We've all see this with the classic triangular prism splitting light.
    [​IMG]
    A hexagonal ice crystal is doing basically the same thing, as it's like a triangular prism with the corners cut off.
    [​IMG]

    The most common form of Halo is the 22° halo, which is the one in the top photo. It's called a 22° halo because of the angle between the sun and the inner edge of the halo. This angle comes about in part because of the angle of the faces in the ice crystals.

    [​IMG]
    http://www.atoptics.co.uk/halo/circ2.htm

    Why it can only be water

    There are several primary reasons why only water can make these halos.
    1) Hexagonal transparent crystals
    2) Refractive Index
    3) Quantity Required
    4) Temporary nature

    1) Hexagonal transparent crystals
    The 22° Halo requires transparent faces which are at 60° to each other. You can only get this with a triangular or hexagonal crystal structure. Water forms hexagonal shapes naturally. No chemicals form triangular crystals. So we can eliminate any crystal substance that does not have a natural sixfold symmetry, such as common table salt crystals:
    [​IMG]

    We can also eliminate any finely milled substance, which would produce irregular shapes with rough surfaces incapable of refracting light. Here, for example, is a fine dust (nano scale on the right) of Aluminum Oxide:
    [​IMG]
    And here's a more typical milled alumina dust:
    [​IMG]

    We can also eliminate commercially manufactured Alumina power, the purest form of which is known as mono-crystalline aluminum oxide, and looks like:
    [​IMG]
    Or nano sized:
    [​IMG]
    Irregular colored crystal will not make a halo.

    We can also eliminate most naturally occurring minerals, as they generally contain impurities that make the crystal either opaque, or they will color or scatter the light, or both.

    The crystals would have to be grown on site from a near 100% pure vapor - which of course is trivial to do with water - as it's the natural process of ice cloud (or ice fog) formation. But a lot harder to do with an artificial substance - especially hard to do with aluminum oxide, with a melting point of 3,762°F (2,072°C). And even then, while aluminum oxide does have some hexagonal geometry from some angles, it does not tend to grow into hexagonal shapes.

    2) Refractive Index

    Ice has a refractive index of of 1.31. Pure Aluminum Oxide crystals (Al2O3, Corundum) has a refractive index of 1.76. The refractive index governs the angle, and so Aluminum Oxide could not make a 22° Halo, because it would refract light at the wrong angle.

    http://www.micro.magnet.fsu.edu/primer/java/prismsandbeamsplitters/equilateralprism/
    [​IMG]

    So if the halo is standard sized, then it's either water, or something with the same refractive index as (frozen) water.

    3) Quantity Required

    Clouds weigh quite a lot, even though they are not very dense, they are very big. Halos essentially form in a fog of cirrus. Cirrus clouds have about 0.03 g/m3 (grams per cubic meter) of water in them. Let's call that 0.01 for a fine ice haze. Now a 22 degree halo extends out a bit from the 22 degree, say 30 degrees. It' generally some around 12 km up, and the sun around 45 degree. This gives an actual circle of ice fog (12*tan(30)) = 7 km radius (being very rough with the geometry here). A thin layer of cloud would be 100m. So that 3.14*7000*7000*100 = 15386000000 cubic meters of ice fog. Multiply that by 0.03 gives 461580000g, or 461 metric tons.

    And that's just if we've somehow just managed to weave the crystals into a small thin patch of sky directly in front of the sun. In the more normal case, the sky is covered with cirrus haze (say 50 km in each direction, which has a thickness of 1km or more. The amount of crystal needed to create such an cirrus overcast is over 200,000 metric tons. This is simply not possible to do with something like aluminum oxide.

    So how is it possible with contrails? A typical plane creates 100-300 metric tons of water from the fuel. Yet an full sky overcast can occur with just a handful of planes. Where is the extra water coming from? The answer is it comes from the atmosphere. The air is at 70% relative humidity, meaning it's already holding millions of tons of water. The addition of the small amount of water from the engine pushes the relative humidity briefly over 100%, allowing the water to condense out in tiny drops, which then freeze. The ice crystals continue to grow from the atmospheric water, adding up to 1,000x their original weight.

    That's simply impossible to duplicate by spraying a crystal powder. all you have is the original crystal, and that's nowhere near enough to cover the sky. A handful of planes would end up 1/1000th the optical density of the equivalent contrail-induced cirrus.

    4) Temporary nature

    Let's say you did somehow manage to loft up 200,000 metric tons of nano-manufactured perfect aluminum-oxide crystals, and ignoring the problems with geometry, and refractive index. Then the next problem is the temporary nature of solar halos. Sometimes they just last for a few minutes or hours. They are there one day, and almost always gone the next, and usually gone much sooner. Where does the overcast go?

    The obvious answer with a cirrus haze is that it evaporates (technically it "sublimes", turning from solid back to water vapour). It does this quite naturally as the air heats up, or as the ice crystals grow large enough to slowly sink into slightly warmer air. It basically just fades away.

    But if some other substance were being sprayed, then where does it go? How can it vanish in a few hours? Of course it can't. Water can vanish because it's basically being re-absorbed back into the atmosphere as water vapor. But a powder of aluminum oxide isn't going to vanish. It's just going to stay there, for many days, until it slowly sinks to the earth. But that's not what we see. So it must be water.
     
    Last edited: Jul 7, 2014
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  2. Ross Marsden

    Ross Marsden Senior Member

    It would be interesting to explore different combinations of RI and crystal shape and see what optical effects are produced. The Atmospheric Optics site has a downloadable application for exactly these experiments. It is called "HaloSim3".
     
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  3. Mick West

    Mick West Administrator Staff Member

    I downloaded HaloSim, but have not found how to change the refractive index.

    I did come across this interesting "ice analog" which could in theory be sprayed out of planes to make a 22° halo:

    http://www.herts.ac.uk/research/str...SRP/ice-scattering/ice-analogue-image-gallery
    The discussion there emphasises just how unique the Hexagonal + 1.31 RI is.
     
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  4. Mick West

    Mick West Administrator Staff Member

    I took this photo at Mammoth Mountain, California, Feb 18, 2008.

    [​IMG]

    Occasionally a halo is accompanies by a Corona, which I also observed.
    https://en.wikipedia.org/wiki/Corona_(optical_phenomenon)
    The one I saw at Mammoth was rather atypical.
    [​IMG]

    Seriously though, since a corona is a diffraction phenomena (i.e. caused by lots of small particles that scatter light of particular wavelengths) then if something were being sprayed in the sky it would create a corona, not a 22° halo (which requires refraction, and hence transparent crystals).

    Because they are usually washed out by the strong light of the sun, Corona's are more frequently visible around the moon, in a layer of clouds. We've all seen something like this:
    [​IMG]

    Solar coronas are more dramatic under more marginal and extreme conditions such as in antarctica, where the clean air scatters the sun less in general which isolates the optical effect of the corona:
    http://ajpadilla.wordpress.com/2013/01/29/2013-a-fresh-start/
    [​IMG]
    The diameter and spread of a corona depends on the size and size variation of the particles, so you can infer some things about the particles from the nature of the corona. Coronea can even be formed from pollen:

    http://www.mysanantonio.com/life/li...-pollen-corona-spectacular-sights-4206774.php
    [​IMG]
    [Note: the term "corona" is more frequently used for the "ring of fire" directly visible around the sun during a solar eclipse, or with a solar telescope]
     
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  5. Mick West

    Mick West Administrator Staff Member

    Particle size is an important consideration for contrails, clouds, halos, and coronas. If a particle is too small, then diffraction phenomena outweigh refraction phenomena. If it's really small, then it will only be affecting light by Rayleigh scattering, and it's practically invisible:

    http://www.google.com/patents/US3517505
    0.5 microns is 500 nm. So for a corona or halo to be visible, the particles have to be bigger than that - i.e. out of the nano range.
     
  6. SR1419

    SR1419 Senior Member


    Did they (AANews) mislabel it as a sundog? Isnt it just a halo?

    http://www.atoptics.co.uk/halo/parhelia.htm
     
  7. Mick West

    Mick West Administrator Staff Member

  8. WeedWhacker

    WeedWhacker Senior Member

    This makes me sad...my "heart" hurts, and my eyes leak water...I think they are called "tears". (not "tears"...I didn't tear anything, I teared up...uh oh, this English language in print is fraught with impossibility and misinterpretation, sometimes...).

    In espanol a "tear" is lagrima. The verb to "tear" is romper.

     
    Last edited: Jul 7, 2014
  9. BigTBoom

    BigTBoom New Member

    Summertime halos are not uncommon either. The Monthly Weather Review would print a list of halo observations every month and there were frequent observations across the country during June/July/August...From Texas to the Dakotas, California to Maine.
     
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  10. Mick West

    Mick West Administrator Staff Member

    Thanks for the pointer. See this article, from exactly 100 years ago:
    https://www.metabunk.org/sk/mwr-042-07-0436.pdf

    [​IMG]

    Says that in Paris, France, a 22° halo (or at least fragments thereof) is visible 130 days of the year (35%, or roughly one day out of three).

    And here:

    https://www.metabunk.org/sk/mwr-046-07-0309c.pdf
    Halos observed in July 1918
    [​IMG]
     
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  11. Raccoon

    Raccoon Member

    WHY OH WHY do those chemtrail [people] spoil the party? WHY?
     
    Last edited by a moderator: Jul 8, 2014
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  12. Joe

    Joe Senior Member

    Iv have seen quite a few over the past few years and all of the time it was because of persistent contrails .Probably more than 50. Have yet to see one without contrails present .
     
  13. solrey

    solrey Senior Member

    Because the conditions that produce the ice crystals (cirrus clouds) which make the halos are also conducive to contrail formation within the same air mass.
     
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  14. Ammon Wade

    Ammon Wade New Member

    Incredible thread, thanks to the education and inspiration to research more! Although it was the title: "Chembows" that made me laugh aloud and read on! For a little instant gratification here is a link to some fantastic photography to complement the theme:
    http://www.weatherscapes.com/gallery.php?cat=optics
     
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  15. WeedWhacker

    WeedWhacker Senior Member

    That's an excellent addition. "Chembow" always brings to my mind bow ties (dunno why) made out of chemicals...although I suppose, that is technically accurate...
     
  16. Here's a halo from reflective glass beads applied to road paint. I guess that counts as a chembow. The halo is more prominent closer to application day.
     

    Attached Files:

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  17. Ammon Wade

    Ammon Wade New Member

    So the glass beads are crystals too? I would like to see some electron microscope of those little things. I can imagine now I need to see what kind of halo I produce if I spray a mist of "Penta Water" towards the sun? The perfect experiment for a bunk-hunting website! :D
     
  18. WeedWhacker

    WeedWhacker Senior Member

    Yeah, fascinating to me as well, but do not expect that some adherents will be 'convinced' by the science. Meaning, what one cannot hold in one's hand and then contemplate and understand? It is increasingly difficult to explain to someone who hasn't had a FULL level of all the required scientific training.

    ETA: As a layperson trying to understand fields of science that I do NOT have expertise in, I nevertheless can grasp at LEAST the basics. Some people cannot.
     
    Last edited: Jul 11, 2014
  19. Mick West

    Mick West Administrator Staff Member

    "Beads" implies spheres, so it sound more like a rainbow type optical effect than a halo.

    Rainbows are created by total internal reflection in tiny drops (spheres) of water in rain or clouds (or garden sprinklers)
     
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  20. Mick West

    Mick West Administrator Staff Member

    You'd have to spray it away from the sun, unless you were somewhere very cold.
     
  21. derwoodii

    derwoodii Senior Member

    some info from http://www.atoptics.co.uk/droplets/glorair.htm and from http://spaceweather.com/

    about this heart shaped halo or called a Glory

    glory_strip.
     
  22. cloudspotter

    cloudspotter Senior Member

  23. Mick West

    Mick West Administrator Staff Member

    Nice. Here I've increased the color contrast, and added an indicator of the perspective of the underlying clouds to make it more clear how the shape formed:
    [​IMG]
     
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  24. SystemX

    SystemX New Member

    I've seen halos/coronas around the sun/moon countless times over the years and it has always seemed natural to me, but this rainbow caught my attention as I've never seen anything like this before. I took this photo a few weeks ago in Los Angeles. Any info much appreciated and thanks in advance. Rainbow Cloud.JPG
     
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  25. Trailspotter

    Trailspotter Senior Member

    Probably, this is (a part of) the circumhorizontal arc (a.k.a., circumhorizon arc).
     
    Last edited: Sep 25, 2015
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  26. Trailblazer

    Trailblazer Moderator Staff Member

    This is an old thread, but I thought I would add these for the record: An exchange of letters in The Times (UK) from August 1944, showing that people have been observing haloes associated with aircraft contrails for over 70 years:

    upload_2014-10-14_18-42-23.
    upload_2014-10-14_18-40-0.
    upload_2014-10-14_18-47-48.
    upload_2014-10-14_18-45-39.

    That should be no surprise, as contrails are cirriform clouds that are ideal for halo formation.
     
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  27. Jay Reynolds

    Jay Reynolds Senior Member

    Can you show how these can be confirmed online or microfiche? The reason why I ask is that so often the believers will try to assert these records are made up.
     
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  28. Trailblazer

    Trailblazer Moderator Staff Member

    Well, I have a paid subscription to the Gale database which includes The Times.There's no free online access. But public libraries ought to have them on microfiche.

    Those are all from the letters page, and all from August 1944. I don't think I made a note of the publication dates (I took those screenshots some time ago when I posted them in the pre-1995 contrails thread) but they'd probably be within two or three days of the dates of each letter. They'd be easy to find in a library.


    Edit: info on the Times Digital Archive here: http://gale.cengage.co.uk/times-digital-archive/times-digital-archive-17852006.aspx

    I imagine quite a few big city or university libraries in the USA would have a subscription.
     
    Last edited: Sep 26, 2015
  29. Trailblazer

    Trailblazer Moderator Staff Member

    Incidentally, a little biographical snippet... I've just been doing a bit of digging and I'm pretty certain that the U. V. Bogaerde who wrote that first letter is one Ulric Van den Bogaerde, the father of Derek Van den Bogaerde — better known as Dirk Bogarde!

    The family had a home in Clayton, Sussex, and there can't have been too many U. V. Bogaerdes in England in the 1940s, certainly not in a small Sussex village.

    image.
     
    Last edited: Sep 26, 2015
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  30. cloudspotter

    cloudspotter Senior Member

    DIY experiments to recreate optical phenomena at home

    Capture.JPG

    https://photonicsdesign.jimdo.com/experiments/
     
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