Rare halos in Taivaanvahti (Rovaniemi, 30th Oct 2015)

[Timo Kuhmonen]

link here, observation by J. Moilanen / M. Riikonen
http://www.taivaanvahti.fi/observations/show/44975

Personnally I have seen the mentioned 87 degree diffuse arc in artifical light halo images (made ultra bright spotlight). Not sure, if this is the first time seen with natural sunlight ? Attached images in observation, do not yet contrain stacking. There was comments, that more will follow...

[Elmar Schmidt]

Thanks!

WHAT IS the 87 degree diffuse halo? Can anyone clarify?

Elmar


PS: thanks Timo, I looked at the simulation, but need to understand. I know, that the 22-deg. halo has a "pseudocaustic" disk extending to 50 degrees, cf.

http://www.atoptics.co.uk/halo/circ1.htm

So, is the 87 deg. diffuse halo the same for the 46 deg. halo?

[Timo Kuhmonen]

On the page of observation --> if you press the small green button with "i" letter on it, you get information of the phemomena and some sample images with simulation results. The button is located inside of frame named "lisätiedot" -> right side of text "Diffuusi 87° kaari"

[Timo Kuhmonen]

If someone has a new halobook (Riikone) this 87 diffuse halo is there described on page 145. Images are shown for the artifical light version of it. It is mentioned to be a diffuse "area" of light which outer edge it is located at 87 degrees away from the point of light source. Also mentioned that triangular crystals producce better this halo.

In the original observation, Moilanen mentioned that he took crystal samples also. So I quess it is worth of waiting the images...

[Timo Kuhmonen]

http://www.taivaanvahti.fi/observations/show/44975

now there is stacked image attached, seen as first one...

[Andreas Möller]

I guess you mean this one? -> http://fs5.directupload.net/images/151101/difmuapi.jpg

[Elmar Schmidt]

So, what is it?

There seems to be nothing much in the literature (except in "Halot").

Elmar

[Michael Ellestad]

Hey Timo,

So cool to see the diffuse 87d arc in natural sunlight I remember seeing this in spotlight displays and was fascinated by this halo. I hope to get some good halos in Ohio USA this winter. I got a couple pyramidal halos, a very nice hi-sun display and two elliptical halos. Wonder what winter will have in store this halo season.

Regards,

Michael

[Timo Kuhmonen]

http://www.taivaanvahti.fi/observations/show/44975

Images 4,5,6 added recently -> stacked images / simulations by M. Riikonen.

[Timo Kuhmonen]

http://www.taivaanvahti.fi/observations/show/44975

Crystal sample photo was now attached -> see image7. For me it is difficult to see, what crystal(s) might be more triangularly shaped (for better production of 87 diffuse arc). Maybe some halo experts could say more....

[Michael Ellestad]

I myself Timo hope to get some good halos this winter

[Alexander Haußmann]

Hi guys,

congratulations to Jarmo and Marko for this remarkable observation!

I've seen the older pictures from the lamplight displays, but could not find the English language blog anymore. I have the "Halot" book, but I don't understand Finnish at all. I can only look at the pictures and guess what the captions say by comparing the halo names, and test my conjectures with the HaloPoint software. As far as I understood, the diffuse 87° halo is created by nearly trigonal crystals in random orientation, along a ray path with one internal reflection. It is rather an intensity cut-off than a clearly defined bright ring, and it does not appear in simulations for hexagonal crystals. This implies that it might be regarded as indirect proof for the presence of non-hexagonal crystals.

It is not the outer rim of the 22° or 46° halo disk, nor the 13-24 pyramidal halo (77°), nor Greenlers "98° halo" (a possible explanation for Hevel's halo). By the way, it adds a new element to this Hevel discussion (is there a 90° halo?).

Best regards,
Alex

[Timo Kuhmonen]

Alex, do you mean some of these blogs, when referring to "english language blog"...?
http://haloreports.blogspot.fi/
https://www.ursa.fi/blogi/ice-crystal-halos/
https://submoon.wordpress.com/

[Elmar Schmidt]

Hello Alex,

still, this makes me ask (again): IS there an outer boundary for the 46-deg halo's pseudocaustic, and if so, at WHICH radius?

Regards, Elmar

[Alexander Haußmann]

Hi Elmar,

the outer rim of the 46° pseudocaustic is located at about 73.5° distance from the sun. The formula is given in the Tape/Moilanen "Angle X" book at page 79.

I was a bit confused that I got a smaller value of 57.8° from a simple in-plane raytracing calculation similar to Vollmer's graph on page 168 of his book. The reason for this difference is that the true maximum deviation is caused by skew rays through the prism.

Best regards,
Alex

[Timo Kuhmonen]

http://www.taivaanvahti.fi/observations/show/44975

also one additional halo marked as regocnised (by J. Moilanen) in this display - secondary 22 tangent arc / Vauhkonen arc -> on image6.

It has earlier been photographed on other display by V. Vauhkonen:
http://www.taivaanvahti.fi/observations/show/26691

[Michael Ellestad]

Timo,

This is turning out to be a great thread keep up the good work