I’ve never seen a full-circle rainbow, but I did once see one of about 190 degrees, dipping into Yellowstone Canyon. Then, a few years after that, conditions were just right that I was able to see a 270-degree one from my ninth-floor apartment. In both cases, the non-sky portions were very faint, because there wasn’t very much depth of rain between me and the ground, but there was enough to be visible.
Sundogs are actually caused by the same ice crystals that form that halo, but when they fall they are oriented by aerodynamic forms so that the axis is vertical. Hence, you only get that portion of the halo to the right or left of the sun.
How the sundog appears depends upon the size of the crystal. If the crystals are small, then the sundogs do indeed appear as yellowish-brownish blobs of light. In that case diffraction effects act counter to the prismatic effects of the crystals and re-combine the colors that the prismatic effect spreads out.
But if the crystals are large, then the sundogs can look spectacular, with rainbow separations of color that can extend horizontally for quite a distance.
Incidentally, sundogs are extremely common. They’re about 10 times as common as rainbows. It’s just that most people don’t know about them and don’t look for them, even when they’re multicolored. I’ve had to point them out to people who were oblivious to them. But a lot of the time the crystals are small, and the sundogs aren’t all that prominent.
Sundogs are only visible, by the way, up to a solar height of about 40 degrees, and they get less likely the higher the sun gets. Your best chance of seeing one is in the morning or evening, near sunrise or sunset. And at such times they can be spectacular indeed.
A wonderful collection, but they’re not all rainbows. I see several that are color-separation atmospheric phenomena that are of very different types. For instance, the one with the colored bands closely surrounding the shadow of the airplane is clearly a glory.
I think that’s what he meant by “lots of different kinds of rainbows”. So far as I can tell, the common English word for “color separation optical phenomenon” is just “rainbow”.
Here’s a different thing we see regularly that I call a virgabow but I suspect is simply a short segment of a bog-standard rainbow seen from an unusual perspective. These two pics are from someplace over the southeastern US.
Without knowing the rest of the setup you can’t say for certain, but it certainly does look like a short segment of a normal rainbow.
Here are a few other phenomena that show rainbow-like color separation
Sundogs (AKA “Mock Suns” AKA parhelia) – if the crystala are large enough
Lowitz Arcs
22 degree halo (if crystals big enough)
Circumzenithal arc
Upper and Lower Tangent arcs
Supralateral arc
Circumhorizontal arc (AKA “Fire Rainbow”)
Colored halos and arcs occur when light is refracted at least once in an ice crystal or raindrop. You see phenomena without color when either the refracting element is so small that diffraction overcomes the prismatic effect, or when only reflection takes place. Examples of uncolored phenomena are:
There was a photo that made the news (or at least “internet news”) a small number of years back that captured multiple forms of rainbow and rainbow-adjacent effects in the one shot. But niw I can’t google it up again. Anyone remember-know where to find it?
What’s so amazing
That keeps us star gazing
And what do we think we might see
Someday we’ll find it
That Rainbow Connection
The lovers the dreamers and me
All of us under its spell
We know that it’s probably magic
Interesting question. Technically, the explanation of rainbows, sundogs, and glories are all really due to interference phenomena. If they weren’t, you wouldn’t see supernumerary rainbows, mistbows, or apparently colorless sundogs. And you wouldn’t see glories at all. But there’s an element of refraction in those, as well, that creates the color-determined path length differences.
In order to get diffraction phenomena you need short path length differences (since the coherence length of natural sunlight is so short) , yet (to meet your restriction) no refraction responsible.
The only example I can think of is atmospheric diffraction around small droplets or fine particles in the atmosphere. You can get diffraction haloes around the sun, or iridescence in clouds.