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PostPosted: Fri Dec 01, 2017 11:34 am 
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Joined: Mon Jan 18, 2010 9:25 am
Posts: 5129
2017 Dec 1 08.51 first noticed to 0854 UT.
There were some lowish fairly fast cumulus, but a complete faintish Very Large bow was seen in blue sky.

Left bottom azimuth 280deg centre 320 or 325 deg right bottom 365 or 370 deg. Houses to elevation 10 deg.
Top of bow ~35 deg elevation.
So horizontally 85 to 90 deg.

No rain, although maybe rain earlier.
No ice on cars, probably due to wind.

No other arcs or halos noticed.

I suppose due to water vapour in the air?

4 photos show complete arc, white with faint colours red outside. 1/400th sec f/4 80 ISO.

Sun low opposite.
Normal rainbow colours? but dificult to see as faintish bow.

08.50 UT wind 010deg 13 kn visibility 40km. cloud few 1,800ft scattered 2,500 ft 3C TDP +00C 1019hPa surface damp. Moderate icing at 7,000ft altitude.

What was this bow?

Regards,
David


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PostPosted: Fri Dec 01, 2017 1:15 pm 
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Joined: Mon Jan 09, 2006 11:05 am
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Location: Lancashire
It was part of the arrow of time :wink: .

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brian


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PostPosted: Fri Dec 01, 2017 3:19 pm 
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It was actually, I think, the rare 46 degree halo.

At 08.51 UT the Sun's elevation was 7 degrees heading 139 degrees SE.
Add 180 degrees gives 319 degrees for centre of halo.
46 degrees less 7 degrees equals 39 degrees, which should be top of halo elevation.

It seems the 46 degree halo cannot be a supralateral or infralateral arc unless the Sun is 15 to 27 degrees elevation.

Regards,
David

P.S.
It would seem that a 46 deg halo, non supralateral arc, is about as rare as a Parry arc, perhaps one hundred times rarer than a 22 degree halo.

I'm pleased I photographed it, but as I have 1200 images on the card and don't know how easily to extract four and stitch them into a mosiac, I won't try.

I think I am lucky to have seen a continuous perhaps 160 degree arc of the 46 degree halo. The lower half of course below the horizon.
The strange thing is that the sky seemed blue with no visible cirrus, although the meteorological report timed 1 minute earlier mentions moderate icing about 20 miles south at a stacking point at 7,000 ft.
Also the air was almost saturated at ground level or 116 ft.


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PostPosted: Sat Dec 02, 2017 8:11 am 
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Joined: Mon Jan 18, 2010 9:25 am
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I made a mistake.

Although the observation was good, my conclusions as to what it was are quite wrong.

It is an antihelion. I.e. opposite the Sun.
So either it was a 46 degree or nearly so antihelion or a rainbow in a clear blue sky with no rain.

Not a fogbow as no fog and 40km visibility and not a glory.

Any ideas?

Regards,
David

P.S.
I cannot find mention of a 46 degree radius antihelion halo.
I have seen all sky halos with halos opposite the Sun.

So it seems to have been a rainbow in a clear sky, which is maybe rare or very rare.
The rainbow seems to have a 40 degree radius for blue light and 42 degrees for red light.
So 84 degrees could be correct, although I thought 92 degree plausible also, as I could not see down to the horizon in the NW or indeed in any direction.

It is mentioned that water droplets can be blown by the wind from quite far away and create a rainbow in a clear sky.

Whatever it was it was very strange.

Regards,
David


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