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Circumhorizontal Rarity

Circumhorizontal Rarity
Photo Information
Copyright: Alan Turvey (liquidsunshine) Gold Star Critiquer/Silver Workshop Editor/Gold Note Writer [C: 186 W: 29 N: 315] (1708)
Genre: Places
Medium: Color
Date Taken: 2010-07-03
Categories: Nature
Camera: Canon 20D, Sigma 20-40 f2.8 EX DG Aspherical, Hoya Skylight (1B)
Exposure: f/11
More Photo Info: [view]
Photo Version: Original Version, Workshop
Date Submitted: 2010-07-22 1:48
Viewed: 2281
Points: 18
[Note Guidelines] Photographer's Note
This is one of those double take moments. I had no idea what I was seeing, so had to get a few shots. It turns out that this is the optical phenomenon - Circumhorizontal Arc, a rare sight in the UK.

I've added a close up workshop post with boosted colour to accompany this one. I also think that this is a first for Treklens.

The following notes are from Wikipedia

Circumhorizontal arc

A circumhorizontal arc is an optical phenomenon - an ice-halo formed by plate shaped ice crystals in high level cirrus clouds.

The current accepted technical names are circumhorizon arc or Lower symmetric 46 plate arc. The complete halo is a huge, multi-coloured band running parallel to the horizon with its center beneath the sun. The distance below the sun is twice as far as the common 22-degree halo. Red is the uppermost colour. Often, when the halo forming cloud is small or patchy, only fragments of the arc are seen.

How often a circumhorizontal arc is seen depends on the location and the latitude. In the United States it is a relatively common halo seen several times each summer in any one place. In contrast, it is rare to non-observable in mid-latitude and northern Europe.

Formation of the halo requires that the sun be very high in the sky, at an elevation of 58 or more, and that the cirrus cloud or haze contains plate-shaped ice crystals. The sun's altitude determines the visibility of the halo; it is impossible to see at locations north of 55N or south of 55S (although a lunar circumhorizon arc might be visible). At other latitudes it is visible for a greater or lesser time around the summer solstice. Slots of visibility for different latitudes and locations can be looked up here. For example, in London, England the sun is only high enough for 140 hours between mid May and late July. Contrast that with Los Angeles with the sun higher than 58 degrees for 670 hours between late March and late September.

The halo is formed by sunlight entering horizontally-oriented flat hexagon ice crystals through a vertical side face and leaving through the near horizontal bottom face (plate thickness does not affect the formation of the halo). In principle, Parry oriented column crystals can also produce the arc, although this is rare.

The 90 inclination between the ray entrance and exit faces produce the well-separated spectral colours.

The arc has a considerable angular extent and is thus rarely complete. When only fragments of cirrus cloud are in the appropriate sky/sun position they can appear to shine with spectral colors.

A circumhorizontal arc can be difficult to distinguish from an infralateral arc when the sun is high in the sky. The former is always parallel to the horizon whereas the latter curves upwards at its ends.

Thanks for looking.

riverfriends, cunejo200, messenger1, vanda, SunToucher has marked this note useful
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Critiques [Translate]

  • Great 
  • AndroK Gold Star Critiquer/Silver Workshop Editor [C: 2110 W: 41 N: 0] (15189)
  • [2010-07-22 1:50]

Hi Alan...
Beautiful view...
Beautiful sky, composition...

Hi Alan:
The combination of the flowerbed field & prism sky is very magical...
Thanks for the notes as well !!!

  • Great 
  • Jan Gold Star Critiquer/Gold Star Workshop Editor/Gold Note Writer [C: 451 W: 139 N: 813] (5358)
  • [2010-07-22 2:26]

Woow, what a great moment have you captured here... And you didn't even know?? You were there on the perfect moment!!!
Thanks for the info in your note!
I love this shot, the colours, the brigthness, the sharpness. I would set the horizon on 1/3...but still love this shot!


Hi Alan,

A very pretty landscape pepperred with the beautiful clouds and sky. Good Note. I enjoyed reading about circumhorizontal arc. I like your pp work here as it appears tempered and the resulting image appear natural. TFS.


Hello, Alan -
I did not get the full effect of the image until I opened the thumbnail and saw the halo more clearly. Very nicely captured with clarity and warm colors throughout. The meadow and sky compliment each other with their opposing types of beauty. I also like the layered effect of dividing the image perfecly in half between earth and sky, accentuated with the added borders at the top and bottom (I usually don't go for added borders, but these ones actually contribute something substantive to the visual effect). Very nice work!

  • Great 
  • vanda Gold Star Critiquer/Silver Workshop Editor/Gold Note Writer [C: 751 W: 47 N: 1333] (7051)
  • [2010-07-22 4:36]

Hi Alan!
Absolutely WONDERFUL!!
Excellent sharp capture. Superb POV and DOF. I love the vivid colours ...and the sky is fantastic!!
This isn't a photo..this is a geat painting!! Perfect format and presentation.
Ciao! Vanda

  • Great 
  • Juliet Gold Star Critiquer/Gold Star Workshop Editor/Gold Note Writer [C: 1250 W: 106 N: 2911] (22323)
  • [2010-07-22 8:41]

Hi Alan,
WHAT a wonderful moment you've captured. I think I would have taken 100 shots of this. Really well composed. The color contrast between sky/flowers and clouds is magnificant. All with a complimentary frame. Congrats on this ! TFS Julie

Hi Alan,
We had one like it a few weeks ago but could not find a spot to capture it a nice way. It is nice to see that you were able to use this with one of those great British flower beds. The simplicity of the composition suits this photo well since it is more about the phenomenon than the rest of the photo. If I do have to find a nit to pick, its the slightly warm while balance used. I feel that a slightly cooler one would bring out the white clouds better and would give the field such a yellow color cast.

Amazing capture !


Great pic! Its good that you also managed to get something interesting in the photo as well as the arc!

I have got a few shots myself that i took of one last year in June and this year at the start of July, and 3 years ago i managed to capture one by moonlight too! The moonlight one was the first i had ever seen, and there were 2 halos around the moon, one was your standard type, the second was off center and slightly warped, and the thrird was near the down low, just above the horizon which was the Circumhorizontal arc, it was an amazing sight! I will post them one day.

It is true that they are pretty rare, although further the south you go in the UK the better it is, and down here on the IOW you are probably at your highest risk of seeing one :-)


Alan: Damn! One helluva explanation of this photograph. Although the left part of my brain could only retain half of the explanatory note, the right side of my brain really appreciated the photograph for all it's beauty and unique tones. Great catch by all stretches of the imagination.

Cheers, JoeGoff,Louisville,KY

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