Circular Apparition

Classical Mechanics Level 3

This appariton is:

Seen through iced up car windshield Caused by frozen, not liquid, spherical raindrops A missile test Planet X approaching Earth An aurora borealis Caused by solar flare & Van Allen Belt Caused by cold air atmospheric refraction Caused by hexagonal ice crystals

1 solution

Michael Mendrin
Jan 6, 2016

This is an ice halo. Unlike a rainbow, where the sun is behind the observer, the sun is at the center of an ice halo. Ice in cold high altitude conditions tend to be like six-sided short pencils or six-sided "coins"--and both contribute to different parts of even more complex but well understood halo formations such as this

Below is a real photograph by David Hathaway, a NASA solar physicist.

Typical halo ice crystals

It can sometimes happen in Singapore. The last time I saw it it was quite a sunny day. Are halos supposed to be possible in the equator?

Julian Poon - 5 years, 5 months ago

Yes, since at very high altitudes, it can be very cold and these kinds of microscopic ice crystals can form. It's more often seen from airliners at cruising altitudes, seen when the sun is shining through high clouds that are formed of such ice crystals instead of water droplets.

Michael Mendrin - 5 years, 5 months ago

There are also the occurance of halo due to water vapour, what makes ice halo different from them?

Tarunbir Singh - 5 years, 5 months ago

Water vapour droplets are still much like raindrops, which is spherical. When you have anisotropic hexagonal ice crystals, the mathematics of scattering is much more interesting!

This was inspired by this Circular rainbows . The correct answer to that one is not because "rain drops are spherical"

Michael Mendrin - 5 years, 5 months ago

IT'S A UFO

Lee Isaac - 5 years, 5 months ago

When elected president, Hillary Clinton promises to investigate. Especially those seen in Area 51.

Michael Mendrin - 5 years, 5 months ago

Really amazing!

A Former Brilliant Member - 5 years, 5 months ago

Is there a difference between Halos and Sun Dogs? Would this phenomenon be more specifically described/defined as a Sun Dog?

Warren Cowley - 5 years, 5 months ago

Sundogs are also called parhelia, which means, "mock suns", so those refer to the parts that look like duplicates of the real sun. "Ice Halo" is sometimes used to refer to all the optical apparitions caused by these ice crystals, but "halo" more commonly refers to "circular halos", the circular or arc parts. Those two terms covers much of the details, but not all. Here's an excellent website that explores ice halos and other atmospheric optics

Atmospheric Optics

Another PDF (long download time) hints at the complexity of atmospheric optics. This is a good introductory text with excellent photographs and illustrations offering short explanations.

Atmosphere Optics

Michael Mendrin - 5 years, 5 months ago

Thanks for the response and additional information. Atmospheric optics is fascinating!

Warren Cowley - 5 years, 5 months ago

@Warren Cowley – In a home I lived when I was a kid, we used to have frosted windows in some rooms, and I would see strange apparitions. After a while, I realized it was due to the anistropic tiny "bumps" in the frosted glass---it wasn't random. So, the first time I saw pictures of these ice halos, I already had a pretty good idea what might be going on.

Michael Mendrin - 5 years, 5 months ago

@Michael Mendrin – That is really cool! As a young person, that kind of phenomena is so wondrous and mysterious - well even as an older person it still is. When I was a child my parents were kind of "hippies". We had a lot of crystals and prisms in our windows. As a result of that, I become somewhat familiar with how light interacts with 3-dimensional angular objects. That made it easier for me to arrive at a correct answer for this question.

Fwiw - my avatar is derived from some light effects in a Redwood grove.

Warren Cowley - 5 years, 5 months ago

@Warren Cowley – I thought it was some Escher hyperbolic disc tessellation

Michael Mendrin - 5 years, 5 months ago

@Michael Mendrin – Yes, it is like that. It is a photo where the light and the trees created some interesting effects. I then used an app on the photo that does hyperbolic tiling on images.

Warren Cowley - 5 years, 5 months ago

I saw it on Discovery Channel.

Shubhang Mundra - 5 years, 5 months ago

Circular Apparition

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