Moon Halo Tonight

[Snowgoose-1]

Quite striking in Essex/Suffolk tonight (Monday, 11th Nov)) .
Can't say I have noticed in the sailing season.

 

[AntarcticPilot]

Halos result from reflections from ice crystals high in the atmosphere.

 

[mjcoon]

Halos result from reflections from ice crystals high in the atmosphere.

If anyone wishes to learn the detail of which, I recommend "Rainbows, Halos, and Glories" [his Oxford comma] by Robert Greenler. books.google.co.uk/books?id=...
I especially liked his experiments with models to study how the collective orientation of ice crystals arises...

 

[AntarcticPilot]

If anyone wishes to learn the detail of which, I recommend "Rainbows, Halos, and Glories" [his Oxford comma] by Robert Greenler. books.google.co.uk/books?id=...
I especially liked his experiments with models to study how the collective orientation of ice crystals arises...

One of my former colleagues at Scott Polar, W. Gareth Rees, is expert in halos, rainbows and sun dogs. But I don't think he's published anything on it. But it's all to do with the orientation and size of raindrops or ice particles.

 

[RunAgroundHard]

If anyone wishes to learn the detail of which, I recommend "Rainbows, Halos, and Glories" [his Oxford comma] by Robert Greenler. books.google.co.uk/books?id=...
I especially liked his experiments with models to study how the collective orientation of ice crystals arises...

At least I know the book is not about Rainbows haloes.

 

[capnsensible]

Halos result from reflections from ice crystals high in the atmosphere.

A number of times seeing that in mid Atlantic, I know I've got a day or two to prepare for a bumpy ride. Traditional way of 'forecasting' an oncoming depression. Weather and crew!

 

[mjcoon]

One of my former colleagues at Scott Polar, W. Gareth Rees, is expert in halos, rainbows and sun dogs. But I don't think he's published anything on it. But it's all to do with the orientation and size of raindrops or ice particles.

Yes, it's evident that because sun dogs are horizontally aligned each side of the sun, the optical path must "know" how gravity is acting!

 

[AntarcticPilot]

Yes, it's evident that because sun dogs are horizontally aligned each side of the sun, the optical path must "know" how gravity is acting!

I understand that it's because ice crystallizes in flat plates (c.f. snowflakes!) and the aerodynamics or whatever makes them fall flat (i.e. with the C-axis vertical for crystallographers!). I've seen well formed snowflakes falling in still air and can confirm that they fall flat. It makes an amazing sparking surface on a glacier!

 

[GHA]

Every day a school day with a friendly AI ​

do optical atmospheric sun dogs know which way gravity is>​

Answer
Optical atmospheric phenomena known as sun dogs (or parhelia) do not possess consciousness or awareness, and therefore they do not "know" which way gravity is. Sun dogs are created through the refraction of sunlight by ice crystals in the atmosphere, typically forming bright spots on either side of the sun within a 22-degree halo. This optical effect occurs when sunlight passes through hexagonal ice crystals that are suspended in cold, high-altitude clouds, bending the light to create the characteristic bright spots
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.While sun dogs themselves do not have any sensory perception or awareness, they are influenced by the physical properties of light and ice crystals, which are subject to the laws of physics, including gravity. The formation and visibility of sun dogs depend on specific atmospheric conditions rather than any conscious understanding of gravitational forces
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.In summary, sun dogs are fascinating optical phenomena resulting from natural processes involving light and ice crystals, but they lack any cognitive ability to perceive or respond to gravity.



write a detail scientific description of how sun dogs form and are visible

Answer

Formation of Sun Dogs​

Sun dogs, or parhelia, are atmospheric optical phenomena that appear as bright spots on either side of the sun, typically within a 22-degree halo. Their formation is primarily due to the refraction and scattering of sunlight by hexagonal ice crystals suspended in the atmosphere, particularly in cirrus or cirrostratus clouds located at high altitudes (approximately 20,000 to 40,000 feet) or even closer to the ground in extremely cold conditions where diamond dust forms
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Ice Crystal Characteristics​

The ice crystals responsible for sun dogs are usually plate-shaped and have a hexagonal structure. When sunlight enters these crystals, it refracts through two specific faces that are inclined at approximately 60 degrees to each other. This refraction causes the sunlight to deviate by a minimum angle of 22 degrees
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• Orientation of Crystals: The orientation of these plate crystals is typically horizontal as they drift downwards through the atmosphere. This horizontal alignment is crucial for the formation of sun dogs because it directs the refracted light horizontally, creating bright spots at 22 degrees to the left and right of the sun
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Light Refraction Process​

As sunlight passes through the hexagonal ice crystals:

1. Entry and Exit: Light rays enter through one edge face and exit through another edge face.
2. Angle of Deviation: The angle of deviation varies depending on how the light interacts with the crystal faces, but for sun dogs, this deviation is consistently around 22 degrees from the sun's position
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3. Color Dispersion: The inner edge of the sun dog appears reddish while the outer edge appears bluish. This color variation occurs because red light is refracted less than blue light; thus, red light remains closer to the sun while blue light disperses further away
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Visibility Conditions​

Sun dogs can be observed anywhere in the world during any season, but their visibility is enhanced under certain conditions:

• Sun's Position: They are most conspicuous when the sun is low on the horizon (during sunrise or sunset), as this increases the likelihood of sunlight passing through ice crystals effectively
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• Atmospheric Conditions: Clear skies with cirrus clouds containing ice crystals enhance their brightness and visibility. In colder climates, diamond dust can also contribute to their formation at lower altitudes
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Related Phenomena​

Sun dogs are often seen alongside other halo phenomena, such as:

• 22-Degree Halo: A circular halo that forms at roughly the same angular distance from the sun as sun dogs.
• Circumzenithal Arc: A rainbow-like arc that appears overhead, caused by similar ice crystal refraction mechanisms
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Conclusion​

In summary, sun dogs are a captivating example of atmospheric optics resulting from specific interactions between sunlight and ice crystals in the atmosphere. Their formation involves intricate processes of refraction and scattering that depend on crystal orientation and environmental conditions, making them a beautiful and scientifically intriguing phenomenon observable under suitable circumstances.

 

[Snowgoose-1]

There's something special when it's just you, the boat, and the moon.

I picked up a mooring one time in Bradwell Creek , next to Peewit Island near Bradwell power station in the Blackwater. Charles Stock of Shoal Waters fame came sailing by on his way home to his mooring NR Maldon.
We exchanged pleasantries and he carried on to St Lawrence the back way. To my surprise, about an hour later, he came past again having sailed in a full circle.I asked why he had gone round again. He sail that earlier it was not dark enough and he wanted to sail home in the full moonlight.

 

[Snowgoose-1]

Hold everything !
I was putting the wheelie bin out tonight and noticed there was no moon .
I did happen to notice a very similar coloured halo around street lights.
I just looked it up on Wiki and it suggests that this is common to people having cataracts .
It happens that only a few weeks ago I had my eyes tested for new glasses and the optometrist
diagnosed a cataract in my left eye.

So in reality, there may not have been a real halo around the moon unless anyone else saw it.

 

[Mister E]

If you close your left eye is the halo still there looking with your right eye?

 

[Snowgoose-1]

If you close your left eye is the halo still there looking with your right eye?

Yes. I later got my wife to have a look at the street lights and she did not see a halo. Perhaps I have an issue with both eyes. Currently I am trying out a new pair of glasses that I need to confirm or otherwise next week. I will mention this to the opticians . I don't suppose it could be the new glasses ? I will have a look tonight with the old ones .

 

[Snowgoose-1]

Looks like I started this thread with duff info. I looked again last night at the moon and streetlamps. All with coloured halos. All eyes, glasses on and off, and one at a time. It might be helpful if any other forumites can see the halos.