Tuesday, August 21, 2007

More on Halo Pics

I sent my halo pics to Jarmo Moilanen, who is a contributor to Halo reports blog.

He wrote to me 'Nice display. You have 22 degrees halo, circumscribed halo and parhelic circle in your photos.' When I thanked him and asked him to please explain a little bit more to me, since I am not very good at halo knowledge yet, he graciously sent me this pic, pointing out the different phenonema going on.

22 degrees halo is in that photo is the faintest halo. It is that inner circular halo around the sun. It is the most common halo.

Circumscribed halo is the brightest halo which is contacting 22 degrees halo on its upper- and lowermost points. The shape of this halo depends on greatly sun elevation. When sun is lower, this halo breaks in two separate arcs. Then they are known as upper and lower tangent arcs (of 22 degrees halo). Upper tangent arc is a V-shaped arc on the top of 22 degrees halo when the sun is close to horizon. When sun is over 70 degrees above horizon, circumsribed halo will overlaping with 22 degrees halo and they are hard to separate from each others. So this halo always tangent 22 degrees halo.

Light ray path through a ice crystal for 22 degrees halo and circumscribed halo are the same, but orientation of the ice crystal are different. That is why they behave and look different.

Parhelic circle is that white reflection halo running through sun at the same elevation than the sun. When parhelic circle is full, it will go around the sky at the same level as the sun.

Wow! So much new information to learn and appreciate. I will definitely be on the look-out for more halos from now on, both solar and lunar ones.


Epijunky said...

That is so cool!

I've never heard of this before...I'm going to look into it.

N. said...

What great timing that you posted all this. I just saw my first halo about a week ago - it looked exactly like yours, but I didn't have a camera - and I couldn't figure out what it could be. It was very clear and lovely.

N. (a normally lurking June mommy from your past)