“Fire Rainbow” over Keppel Henge but don’t call it that!

The fifth annual solstice celebration was held on Saturday June 21. And for the five years it has been held, we have only been clouded out once. This year as an added attraction what is incorrectly called a “fire rainbow” appeared for an hour or so just as the celebration was coming to an end. Luckily at least two photographers were still on the scene to record the event.

The website
www.atoptics.co.uk/halosim.htm gives all the details about how it forms (hexagonal ice crystal in cirrus clouds are responsible for many halo phenomena) and it gives the more correct term “circumhorizon arc” or if it extends all the way around the sky (rare) it is a “circumhorizon halo”.

It was first noticed just after the pointer shadow passed the base of the summer solstice stone at 1:25 pm (solar noon) and I watched it finally fade away around 2:45 pm or so by the time I got back to Owen Sound.

The term “fire rainbow” is totally incorrect because it is neither a rainbow (which is caused by water droplets) nor on fire but reporters have latched onto the description because it does look like a rainbow on fire. The second image below illustrates that quite nicely. Image taken over Owen Sound June 2004 by yours truly.

There is another halo (arc really) called the circumzenithal arc that appears
above the sun on some occasion, but its colours are reversed. Both the 22° halo and circumhorizon arc have red on the outside of the colour band. The circumzenithal arc's colours are the opposite. So check out the view straight up so you don't miss that one.

One other note is that these arcs occur only when the sun is high in the sky (summer) and there are cirrus (ice) clouds present. With a low sun, you may see the CZA but not the CHA. Solar noon on summer solstice fits the bill nicely.

John H.

Images below by JH June 2014 and June 2004


Circumhorizon arc_June 2-04-untitled-14_986K