[JoeF]

Jim Terry started a thermaling thread over at Sam Kellner’s Club page. There I too had added thermal locating tricks.

Great, Bill,
we then join the topic thread: https://ushawks.org/forum/viewtopic.php?f=17&t=1000

[DaveSchy]

On several occasions, in thermals and high, I have seen my shadow on the ground is surrounded by either a faint glory or a ring diffraction "shadow" a few wingspans wide.
I've considered it an effect of being in a parcel of air that is thinner (warmer) than the surrounding air, plus sunlight diffraction from a white upper surface wing.
I observed it the most going XC in Chelan in the summer...
I wasn't hypoxic, but I was definitely in go far adrenaline mode

[DaveSchy]

I have also seen this effect on hot days west of the cascades. By high, I am referring to altitude. I think it possible to visually detect thermals, but a decent vario confirms "seat of the pants" detection, and is better for coring because the audio (and some experience) is all we need!

[KaiMartin]

On several occasions, in thermals and high, I have seen my shadow on the ground is surrounded by either a faint glory or a ring diffraction "shadow" a few wingspans wide.

The shadow with a surrounding glory was most likely an instance of Brocken spectre. This is a an optical phenomenon named after the mountain range Brocken in Germany.
The glory is a result of an increased ability of spherical droplets of water to scatter sun light back to where it came from. You were looking at your shadow. So directly next to the shadow you s light that is scattered almost but not quite back to sun.

It does not take much fog to make for a visible effect. A hunch of moisture over the trees may be sufficient.

See the wikipedia article for more details.
https://en.wikipedia.org/wiki/Brocken_spectre

---<)kaimartin(>---

[JoeF]

Thanks, Kai
http://www.kevincosley.com/hang-gliding