Stargazing Small angle lunar haloes

[Bandersnatch]

Yesterday night I watched the Moon. It was surrounded by a set of haloes, relatively small in diameter. I didn't take a picture.
I understand the cause of the 22-degree halo, but I don't know what causes those smaller haloes.
These were approximately within 4-6 degree in radius from the Moon. The central one was disc-like, bright throughout the area. The remaining one or two (I can no longer remember clearly) outer ones were circular, separated by darker gaps.
The sky was clear, and the effect persisted throughout the night.

 

[Tom.G]

A couple possible explanations:

Those multiple halos were do to the Moon light passing thru both water droplets (fog) and ice crystals in the atmosphere; or passing thru either one of these that was present at different altitudes.

Cheers,
Tom

 

[Ian Telcher]

Yesterday night I watched the Moon. It was surrounded by a set of haloes, relatively small in diameter. I didn't take a picture.
I understand the cause of the 22-degree halo, but I don't know what causes those smaller haloes.
These were approximately within 4-6 degree in radius from the Moon. The central one was disc-like, bright throughout the area. The remaining one or two (I can no longer remember clearly) outer ones were circular, separated by darker gaps.
The sky was clear, and the effect persisted throughout the night.

The haloes will vary in size according to the thickness and density of the cold air and moisture particles in the regen, whether they are frozen or not; it's just a matter of refraction and defraction. If you could observe the haloes from a longer distance, they would be more defused and larger in size.

 

[Andy Resnick]

Yesterday night I watched the Moon. It was surrounded by a set of haloes, relatively small in diameter. I didn't take a picture.
I understand the cause of the 22-degree halo, but I don't know what causes those smaller haloes.
These were approximately within 4-6 degree in radius from the Moon. The central one was disc-like, bright throughout the area. The remaining one or two (I can no longer remember clearly) outer ones were circular, separated by darker gaps.
The sky was clear, and the effect persisted throughout the night.

I wonder if you saw a corona:

https://www.atoptics.org.uk/droplets/cormoon.htm
https://www.atoptics.org.uk/droplets/corona.htm

I've seen similar rings on occasion- AFAIK, they form when the intervening droplets/ice crystals are very uniform in size.

 

[Bandersnatch]

Thanks everyone. Corona does look similar.
Have any of you seen it worked out somewhere how the droplet size relates to the angular size of the corona, or how that outer ring forms (I'm assuming it's something similar to the rainbow mechanism). In a textbook maybe? I'd like to nerd it out a little.

 

[Andy Resnick]

Thanks everyone. Corona does look similar.
Have any of you seen it worked out somewhere how the droplet size relates to the angular size of the corona, or how that outer ring forms (I'm assuming it's something similar to the rainbow mechanism). In a textbook maybe? I'd like to nerd it out a little.

I think it's a straight diffraction problem, similar to powder diffraction or scattering by colloids. IIRC, the angular diameter of the rings depends on the droplet size, the ring spacing depends on the average spacing of droplets, and multiple rings indicate good monodispersity.

I don't think it's a case of Mie scattering (that's responsible for backscattering phenomena like glories)

Apparently non-spherical aerosols (like pollen) produce non-circular rings:
https://www.atoptics.org.uk/droplets/pollen1.htm