1. Mick West

    Mick West Administrator Staff Member

    feebdcce0b16d6b6c70852ac8e2d7538.

    The above image is one of the earliest representations of a solar halo and two sun dogs (also called parhelia, or "mock suns"). It's from 1520, and looks like it was painted from memory, or from a verbal description. Here's a more modern photograph of a similar configuration
    [​IMG]

    Halos and sun dogs are formed by ice crystals refracting the light of the sun. They form at specific distances from the sun (due to the angles of the crystal, and the degree to which it bends light). The most common (and smallest) halo forms at 22° around the sun, and hence is known as a 22° Halo. Sun dogs form on either sides of this halo, level with the sun. Sometimes they look like small segments of a rainbow, and sometimes they are very bright, almost as bright as the sun (especially if there is some cloud in front of the sun

    People's experiences with halos and sun dogs varies by individual. I remember quite vividly the first time I saw a halo, in 1996, somewhere near Fresno, California. I saw them occasionally when living in Los Angeles, but I noticed a distinct increase in the frequency when I moved 350 miles north to the Sacramento region.

    Many people don't notice halos simply because they are so close to the sun, and people avoid looking at the sun, because it hurts your eyes. Halos are best observed when part of the sun is obscured, or indirectly with a digital camera.

    So how common are halos? How common are sun dogs? Has the frequency of these things changed over time?

    In this excellent time-lapse video, Patrick Roddie documents the occurrence of halos on 21 days in March 2015.

    Unfortunately Mr Roddie incorrectly describes the halos as "sun dogs", when in fact no sun dogs appear in the video. But from this we can deduce that halos are fairly common in San Francisco in March, and sun-dogs less so.

    But what does history tell us about the frequency of halos and sun dogs? There's quite a history of descriptions of these phenomena, going back hundreds of years.

    Notes on historical terminology:
    • In some places halos and sun dogs are referred to as "meteors", which is an old-fashioned term for anything seem in the sky, and not just meteorites)
    • Older books use the terms "halo" and "corona" interchangeably. In more modern usage the term "corona" is used for the irregular rings of iridescence seen much closer to the sun than with halos.
    • Sometimes the size of the halo is referred to by the angular diameter, and not the radius. A normal halo has a radius of 21.7°, usually referred to as 22° halos. But in older works this might be referred to as a 44° diameter halo, or even approximated as "about 45° diameter"

    The oldest reference to halos and sun dogs is from Aristotle's meteorology, which was written over two thousand years ago. While his speculation about causes might be a bit off, his observations are fairly accurate. He has quite a long section on this topic.
    http://classics.mit.edu/Aristotle/meteorology.3.iii.html

    A Goodly Gallerye with a Most Pleasaunt Prospect: Into the Garden of Naturall Contemplation, to Behold the Naturall Causes of All Kynde of Meteors
    , William Fulke: 1563
    " (with an archaic spelling, "Halon"):
    http://books.google.com/books?id=ebpCAQAAMAAJ&vq=halo&pg=PA34#v=onepage&q&f=false
    [​IMG]
    Encyclopedia Britannica, Volume the Third, 1773
    https://books.google.com/books?id=Ow8UAAAAQAAJ&pg=PA457#v=onepage&q&f=false
    [​IMG]



    Or 1813:
    https://archive.org/stream/researchesabouta00forsiala#page/100/mode/2up
    [​IMG]

    https://archive.org/stream/researchesabouta00forsiala#page/n479/mode/2up
    [​IMG]

    Encyclopedia Brittanica, 1823
    https://books.google.com/books?id=vVQ0AQAAMAAJ&dq=encyclopedia britannica halo&pg=PA673#v=onepage&q=encyclopedia britannica halo&f=false
    [​IMG]

    The Florida Night Sky, 2002
    https://books.google.com/books?id=0NK98MUpOG4C&lpg=PA65&dq=parhelia rare common&pg=PA65#v=onepage&q&f=false
    [​IMG]

    Color and Light in Nature, 2001
    https://books.google.com/books?id=4Abp5FdhskAC&lpg=PA171&pg=PA171#v=onepage&q&f=false
    [​IMG]
    [​IMG]

    The Atmospheric Optics web site give figures for the frequency of the various types of halo in days per year, with the 22° halo being 100 days per year, which is about twice a week. Parhelia (sun dogs) are seen once or twice a week. This will vary by location and time of year.
    http://www.atoptics.co.uk/halo/whyinfr.htm
    [​IMG]

    The figures are also averages. This does not mean you will see halos exactly twice a week. You might see none for a month and they see them every day for two weeks. See: http://personal.inet.fi/koti/luuk3/halot/
     
    Last edited: Jan 4, 2017
    • Like Like x 2
  2. Sagittarius

    Sagittarius Member

  3. M Bornong

    M Bornong Senior Member

    The KJV, Ezekiel 1:28 (http://biblehub.com/ezekiel/1-28.htm)

    Was this one of the earliest mentions of a solar halo? The Book of Ezekiel is thought to have been written around 590 BC. Not long before the Greeks mentioned them.

    Ezekiel.
    http://www.sci.ccny.cuny.edu/~stan/skyart.html (chapter 3)
     
    • Informative Informative x 1
  4. M Bornong

    M Bornong Senior Member

    Earthquake lights. :) We did have an event not long and not too far (200 miles, from Patrick's POV, of course, as far as I know they were unrelated.
    http://earthquake.usgs.gov/earthquakes/eventpage/ci37528064#general_region USGS.

    It seems, atmospheric conditions throughout a good portion of California were conducive for refraction and diffraction events to occur. I caught this sundog a few minutes before 5:00 pm,

    DSCF1333.JPG

    Using the method describe on http://www.atoptics.co.uk/halo/circular.htm

    22halo.

    It was a sundog, with a portion of a 22° halo. It faded quickly, as the sun sank. 3 minutes later another "rainbow" appeared double the distance, away, it wasn't as brilliant, and you need to look close.

    DSCF1339.JPG
    Last night, the reaction to this atmospheric phenomenon wa a bit different. Last night, for the first time, people in my area first reported to the news stations, how they looked up to the sky and found something wrong.

    kgetdutch.

    This is one of the most interesting reactions to the sundog, I've found.



    The original video with these comments, can be found, here. https://www.facebook.com/mark.ortiz.142/videos/1278557218827443/?pnref=story

    MarkOrtiz.

    I sure wish these people would take a look at this page, http://www.atoptics.co.uk/
     
    Last edited: Feb 24, 2016
    • Agree Agree x 1
  5. john Mont

    john Mont New Member

    Actually I have seen more around the moon than the sun.
     
    • Agree Agree x 1
  6. Mick West

    Mick West Administrator Staff Member

    They are much more noticeable around the full moon, as they are against a darker background. But there's probably more around the sun, just fainter - and then the sun is "full" every day.
     
    • Agree Agree x 2
  7. Gridlock

    Gridlock Active Member

    Googling "ion engines" gives some interesting reads. Googling "color change atmospheric molecules", less so.
     
  8. Mick West

    Mick West Administrator Staff Member

    Halos and sun dogs are not the result of individual molecules though (which would cause scattering), they are the result of relatively large ice crystals, which cause refraction.
     
    • Like Like x 1
  9. Gridlock

    Gridlock Active Member

    Sorry, yes, I was being obtuse - my point was the Facebook poster leapt to the conclusion that this was "an ion engine jumping" despite obviously having a tenuous grasp on basic scientific principles and terms.

    The second search term would at least have eventually led him to, umm, enlightenment but confirmation bias is a very real thing.
     
  10. cloudspotter

    cloudspotter Senior Member

    • Useful Useful x 4
    • Informative Informative x 1