Wednesday, 7 November 2007

Pyramidal crystal halos

A funny coincidence that a halo-observer may want to experience is travelling to Egypt and seeing some pyramidal crystal halos.

This odd-radius display was photographed by Márk Laczkó of Budapest, Hungary somewhere over the southern borders of Romania. He was sitting on an airplane heading towards Egypt on 27th October. When he realised they were flying in cirrus clouds, he deliberately started looking for some halo phenomena. The surprisingly well distinguishable 18°, 20°, 23° and 24° halos were visible for about a minute at 06:21 UTC. Unfortunately, there is no documentation or report of a possible 35° halo. The original photo and two other pictures are also available (#1 and #2).


  1. Here are three halos at approximately equal distance from each other. Normally 18° and 20° are sort of grouped together, not so easy to distinquish from each other. This strikes me as a strange display. .

  2. Are these really halo's? It seems to me that the red color is on the outside-region of the arc and not in the inside-region.

    Couldn't it be just some interference in the window of the airplane???

  3. To my eye the colors are on the inside, assumung the sun in on the right. Nevertheless, interference fringes were my first thought as well. But upon looking at the non-encahnced images they just seem more like halos. It looks like the intensity variations follow the irregularities in the cloud.

    If we would know the angular dimensions of the photo field of view, that might help in resolving the issue. Ágnes, is there exif-data available?

  4. Thanks for the exif, Ágnes. This was photograhed with the high end of zoom , 29.2 mm, equivalent of 140mm in 35mm frame. shows a simulation of 18°, 20°, 22° stuff in 140mm frame (made with Jukka Ruoskanen's software). Certainly this is a halo display. The bright 20° halo combined with high focal lenght of the lens account for the good separation of halos in this display.

    And of course, we should also pay attention to what the observer says: these phenomena were visible for about a minute. Such a short manifestation would be less likely with interference in the window.

  5. Thanks for the simulation, Marko! It looks good. The red is certainly inside in these images, but it's absolutely true that the separation of the halos is very interesting and looks quite unusual at first sight. Now we know the reason.