Sundogs and halos!

December 10, 2017 • 2:30 pm

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:

19 thoughts on “Sundogs and halos!

  1. 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.

  2. 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.

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

  4. 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.

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

    2. I just got:

      “Kaleidoscope Sky”
      Tim Herd
      Abrams
      New York, 2007

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

    3. 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 http://www.blueskyassociates.com

  5. 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.

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