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Round Rainbow

Beth

Philosopher
Beth
Joined
Dec 6, 2004
Messages
5,598
On a recent flight, it was a sunny day with some scattered clouds as we came in for a landing. I was looking out the window and observed a round rainbow as the clouds passed a bit below the plane while flying at a particular angle to the sun. It was quite breathtaking, though I never glimpsed the entire circle at once - the clouds weren't large enough. Instead the circle appeared to be steady beneath my window and the clouds would reflect different parts of it making a complete circle as we passed over them.

It didn't last long. When the plane turned, I didn't see it any more. It was quite beautiful. I wondered if anyone else has observed such a phenomon and if anyone knew of the explanation for the appearance of a full circle. I've heard that the arch of a more traditional rainbow is a circular arc, but I've also seen a flat almost ground-hugging rainbow in Hawaii, so I know they don't have to be circular.
 
In order to see a full circle 'bow you have to have water droplets suspended in a circle of large enough diameter - a total angle of 84 degrees or nearly a full octant of your view - directly opposite the sun. In general the ground gets in the way for most observers (that is, the ground vastly shortens the distance view so not very many droplets can exist between the observer and the ground. The total requirements then is for the sun to be above the horizon and to have sufficient water droplets throughout the whole octant opposing the sun. Obviously in an airplane the chances are much better of getting that to happen, particularly at high sun angles. The view will be towards the ground, always.

One other possibility might be at near noon on a precipitous mountain peak surrounded by clouds below you. But watch your step!
 
We have tons of rainbows out here, so I have probably seen just about every type including the circular (also from an airplane), almost completely circular (hiking on Haleakala), and my personal favorite, a true moon-cast rainbow (not the ring around the moon variety). My husband and I were hiking at night on the Big Island and were watching the full moon. When we turned around to leave, we saw a faint, misty rainbow!
 
So far, my favorite has been a double rainbow - two rainbow arcs with a bluish-grey section between them.
 
I may be misremembering it, but I thought when we were kids it was possible to see a complete circle by spraying mist out of a garden hose. I don't see why that wouldn't be possible, even if I am misremembering it.
 
Yes, a garden hose at noon makes a fine circle. You are in the middle of the circle.
 
Jeff, thanks for the link and Shadron, thanks for the basic explanation. I figured it had to do with the angle of the sun and the plane, but I didn't know it had been computed so exactly.

Hokulele, the moon rainbow sounds fabulous, I've never heard of that, but I'll be on the look-out for it if I'm ever in that situation (unlikely though :( ). Bluess, double rainbows were my favorite too until this one! When I've seen them, usually one rainbow was noticably brighter than the other. I saw a double once in the Rockies with one arch that was more brilliantly colored than any other rainbow I've ever seen. Usually they're rather pale.
 
Beth said:
Jeff, thanks for the link and Shadron, thanks for the basic explanation. I figured it had to do with the angle of the sun and the plane, but I didn't know it had been computed so exactly.

Hokulele, the moon rainbow sounds fabulous, I've never heard of that, but I'll be on the look-out for it if I'm ever in that situation (unlikely though :( ). Bluess, double rainbows were my favorite too until this one! When I've seen them, usually one rainbow was noticably brighter than the other. I saw a double once in the Rockies with one arch that was more brilliantly colored than any other rainbow I've ever seen. Usually they're rather pale.
Click to expand...

Did you see a rainbow or a glory?

Follow the links to see some incredible photos and find out more than you ever wanted to know about rainbows and similar atmospheric phenomena.
 
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There is not pot of gold at the end of a rainbow, at least none without digging.

I was at Niagara Falls on the Canadian side, by the railing. Looking away from the falls towards the city I saw a rainbow arcing from the far horizon straight towards me, over my head. I turned around and followed as it curved down right in front of me.

Looking down I saw it hit the cliff face about 15m bellow my feet.
 
Beth said:
Bluess, double rainbows were my favorite too until this one! When I've seen them, usually one rainbow was noticably brighter than the other.
Click to expand...
One is usually brighter, and the sky between them appears darker than the sky on either side.

ETA: And the spectrum of the two runs opposite directions - ROYGBIV in one, VIBGYOR in the other.
 
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Kestrel said:
Did you see a rainbow or a glory?

Follow the links to see some incredible photos and find out more than you ever wanted to know about rainbows and similar atmospheric phenomena.
Click to expand...

It was a glory. Thanks so much! It's very nice to find out the name of the phenomena I saw. The pics on that page are awesome too!
 
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