Tuesday, October 28, 2008

Stunning solar halo over Porto

From ice and sunlight amazing things will come...

I'm going to do a full Porto blogpost soon, but I needed to get this out before anything else, as anyone who knows me will understand.

Sunday afternoon I was in the gardens of a wonderful modern art museum in Porto (Serralves), walking around and taking in the sun with a friend of my couchsurfing host.I looked up, as I seem to spend most of my time doing and caught a glimpse of a solar halo beginning to form. We got out into an open area and watched as the upper arc of the solar halo turned into the most stunning display I've ever seen.

As the field of ice in the clouds swept across the sun, for around half an hour the sky was illuminated with the most stunning arcs, halos, sundogs and perhelia I could imagine. Of course I got a ridiculous number of photos of this and have only gone through some of them in detail. In particular it appears that the pictures of the sundog may have captured a phenomenon rarely captured on film. As explained to me by the author of the superb site atoptics when I sent him the photos:

'...But something about your image caught my eye. I then severely enhanced it and have attached the result. It looks to me as though you have the very rare Lowitz arcs and have unusually captured the upper, lower and middle Lowitz components. See the very first Lowitz image for comparison..'
This effect was first captured here, but it seems possible that I may have caught it too.

On top of the 22 degree halo, the upper tangent arc and the sundog, there was a lovely 120 degree parhelion, something I'd never seen before. Having spent some time reading atoptics in the past I had a good idea where each of these effects was coming from and to see them so vividly was wonderful! Each part of the pattern comes from a particular shape of ice crystal with a given orientation and a specific path of light, sometimes through the faces and sometimes through the edges.

Of course I told those around me about the amazing display in the sky but all but two of them showed no interest at all, looking up and then seeming rather surprised that I'd bothered them about it.

Anyway, here are a few of the pictures I took of this startling sight:

The upper tangent arc, the 22 degree halo and the sundog:

22 degree halo, upper tangent halo and sundog
The halo, the sundog and the parhelic circle:
Sundog and Parhelion
The sundog, the parhelic circle and the 120 degree parhelion:
sundog and 120 degree parhelion
and the 120 degree parhelion shining brightly. It seems that as noted occasionally before, this has a faint redish tinge to it (only seen on the zooms):
120 degree parhelion
All of the above images can be seen in larger sizes by clicking. There are also currently a great number more photos on my flickr account as I've simply dumped them up there for now for further analysis.

I have mixed emotions about this. On the one hand I was overwhelmed with the sight, grinning and running around like a kid in a sweet shop for half an hour, while on the other I'm saddened by the lack of interest most people have in the wonders of nature. Still, in a few weeks I will be doing my bit by giving a lecture to the whole physics department on atmospheric optics. I hope to get another few people enthused by what is out there!


Bárbara said...

Although i wasn't there to watch that wonder with you, i can tell you that i have already googled sun halo to find out more about it!

Unknown said...

Hi Bárbara, great that I've got a few people in Porto interested in this :-)

Keep an eye out, I have a feeling you may be in a good spot to see such things over the winter.

Anonymous said...

I saw a moondog AND a Blue moon (http://en.wikipedia.org/wiki/Blue_moon) last year in India during the monsoon season, and I can understand the "kid in a sweet shop" mood perfectly. This must have been really amazing, thank you for the pictures :)

Etelvina said...

I saw a perfect solar halo at porto today :D
Thanks for sharing your knowledge with in that day. (unfortunately I don't have any pictures)