Weather story or question?
Have a look at this! A series of circles appeared around the sun over the Comox Valley today which, as CTV videographer Gord Kurbis put it, looks like “Mother nature went a bit crazy with the ol’ Spirograph.”
VIDEO: Unusual halos around the sun right now in the Comox Valley. A bit hard to shoot on video but sort of looks like Mother Nature when a bit crazy with the ol' Spirograph. I'm sure @CTVNewsAstrid will have an explanation for @CTVNewsVI viewers on this. pic.twitter.com/2OO9DT634h— Gord Kurbis (@CTVNewsGord) May 30, 2018
Gord you know me so well! Yes, I do have an explanation for this.
Most of us are familiar with the 22° halo. That’s the perfectly circular halo around the sun. See the oval one? That’s called a circumscribed halo. If it was right overhead it would be circular, but it’s not. It’s oval in shape because, in this case, the sun is about 60 degrees above the horizon.
Both the 22° halo and the circumscribed halos are made of ice crystals that are cylindrical and hexagonal in shape. Think of the shape of a pencil. The 22° halo has the crystals randomly oriented, while the circumscribed halo needs them to be oriented the same way. So the light enters one side and exits a different side, but not the end faces. The way the light travels and bounces, no light is reflected towards the inside of the ring, which makes the sky inside the halo noticeably darker.
This tweet shows both the halos, as well as an infralateral arc.
An infralateral arc is formed when light enters the side of the pencil-shaped ice crystals and comes out the end face.
As for the white band that goes through the sun and the halos – that’s called a parhelic circle or arc.
The ice crystals in this scenario need to be shaped like hexagonal plates. Rays of light bounce around the ring of faces inside. The colours of light are split apart and then mixed back together so the colour is generally white.
Last but not least this one.
This graphic is helpful in showing how these all come together:
Huge thank you to Ed Wiebe at UVic’s School of Earth and Ocean Sciences (who also runs the Vancouver Island School-Based Weather Station Network) for helping me sort out all these sun circles.