Sundogs and halos!

Here’s a lovely Sun halo from December 1 sent to me by Matthew Cobb (be sure to click on the arrow to see the video). You can see why such phenomena were once taken to be evidence for God or the supernatural.

What causes these things? Wikipedia says this:

The ice crystals responsible for halos are typically suspended in cirrus or cirrostratus clouds high (5–10 km, or 3–6 miles) in the upper troposphere, but in cold weather they can also float near the ground, in which case they are referred to as diamond dust. The particular shape and orientation of the crystals are responsible for the type of halo observed. Light is reflected and refracted by the ice crystals and may split up into colors because of dispersion. The crystals behave like prisms and mirrors, refracting and reflecting light between their faces, sending shafts of light in particular directions.

And here’s a 22-degree halo seen from Annapurna Base Camp. I’d love to see something like this:

Wikipedia‘s explanation:

Among the best-known halos is the 22° halo, often just called “halo”, which appears as a large ring around the Sun or Moon with a radius of about 22° (roughly the width of an outstretched hand at arm’s length).

But what’s really amazing is this from EarthSky (my emphasis):

These clouds contain millions of tiny ice crystals. The halos you see are caused by both refraction, or splitting of light, and also by reflection, or glints of light from these ice crystals. The crystals have to be oriented and positioned just so with respect to your eye, in order for the halo to appear.

That’s why, like rainbows, halos around the sun – or moon – are personal. Everyone sees their own particular halo, made by their own particular ice crystals, which are different from the ice crystals making the halo of the person standing next to you.

Here’s a longer video of the event at the top, courtesy of reader Vera:


  1. yiamcross
    Posted December 10, 2017 at 2:43 pm | Permalink

    Quite literally awesome.

  2. kirkwoll
    Posted December 10, 2017 at 3:02 pm | Permalink

    I saw one for the first time last week. Took this one above my roof.

    • Taskin
      Posted December 10, 2017 at 3:05 pm | Permalink


  3. Taskin
    Posted December 10, 2017 at 3:03 pm | Permalink

    Spectacular video, I would love to have seen that! 🙂

  4. Posted December 10, 2017 at 3:15 pm | Permalink

    Wow! That is stunning!!! Thanks for sharing.

  5. Posted December 10, 2017 at 3:21 pm | Permalink

    I saw that video on YouTube on December 2, absolutely spectacular and breathtaking, lucky Swedes!

  6. ploubere
    Posted December 10, 2017 at 4:14 pm | Permalink

    I’ve seen fainter halos, but never as good as these.

  7. Posted December 10, 2017 at 5:07 pm | Permalink

    In 1460-something-or-other, three suns rose on what would be the battlefield of Mortimer’s Cross: this example of parhelion allegedly so terrified the forces of Henry vi that they were soundly beaten by the forces of the future Edward iv. I have no idea if there is any truth in this or if this was just propaganda.

  8. Posted December 10, 2017 at 5:31 pm | Permalink

    Constantine has allegedly seen a cross in the sky, at the Battle of the Milvan Bridge, which brought humankind in great trouble.

    Other than that, everything we see is personal in the same sense as described above. In the same way, every rain is personal, not only do we perceive different raindrops on our face, also each photon bouncing off anything can only rain into one eye and kick off an electron from a Rhodopsin.

  9. rickflick
    Posted December 10, 2017 at 6:27 pm | Permalink

    You can sometimes see a similar effect from an airplane. Its usually seen where the plane’s shadow skims the lower clouds.

    • allison
      Posted December 11, 2017 at 10:47 am | Permalink

      This phenomenon is called a “glory”

  10. ThyroidPlanet
    Posted December 10, 2017 at 6:42 pm | Permalink


  11. Posted December 11, 2017 at 12:53 am | Permalink

    The definitive book on this subject is “Rainbows, Halos and Glories” by Robert Greenler (Cambridge University Press, 1980). It contains many colour photographs of the phenomena, including rare and unusual variants, along with clear and (mostly) non-mathematical explanations. I can strongly recommend it. Unfortunately, it’s no longer in print, but second-hand copies can be found easily enough.

    • ThyroidPlanet
      Posted December 11, 2017 at 8:09 am | Permalink

      Because of this comment, I decided to scoop up a few titles on this topic from the local bibliothéque! No Greenler yet, but hanks!

    • ThyroidPlanet
      Posted December 15, 2017 at 5:59 am | Permalink

      I just got:

      “Kaleidoscope Sky”
      Tim Herd
      New York, 2007

      … another “why haven’t I seen such a book before” moment.

    • ThyroidPlanet
      Posted December 16, 2017 at 3:12 pm | Permalink

      Well heres something interesting

      I got “Mathematics in Nature” by John A. Adam, 2003, Princeton U. Press, and on p.82, Figure 5.2, it says (Oxford comma trigger-warning) “Rainbows, Halos and Glories” … Robert G. Greenler … now available through

  12. Liz
    Posted December 11, 2017 at 9:17 am | Permalink

    So beautiful.

  13. allison
    Posted December 11, 2017 at 11:17 am | Permalink

    Halos in general are not rare phenomena – I’ve seen them hundreds of times where I live (metro Atlanta). You just have to look up at the sky, which most people don’t do very often! For a halo to be present, you need to have some high, thin clouds or haze in the sky. Based on my observations, they are much more common during the colder months.

    Some displays are much more elaborate, with various rare features present – there’s a whole zoo of them. I can remember a spectacular display on a December afternoon in the late 1980s during which some of the rarer phenomena – including the Parry arc and the circumzenithal arc – were visible.

  14. Posted December 11, 2017 at 12:41 pm | Permalink

    I’ve wondered why the phrase “sun *dogs*” ever since I read about them as a child.

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