I’ve never seen one, or known anybody that has seen one,
but have seen the word used in non-scientific (poetic) contexts.
Do they exist?
This would seem to require a couple of things.
I thought moonbow might just mean a halo around the moon, but a search on Lycos turned up this. Yup, they exist.
Physically it is possible. Best results, given what I know about refraction, would be when there is a full moon and you’re between it and a rainstorm.
I’m assuming the moon reflects the full spectrum as it appears white when up in the sky; if it absorbed any part of the spectrum it’d be a different color.
I’ve never seen one, either, but like I said, it does seem possible.
This site says that you can see a moonbow on the night of any full moon in the spray of a waterfall in Kentucky:
http://www.geocities.com/RainForest/Canopy/9919/
I imagine moonbows caused by moonlight shinging through rain are possible but likely rare events. For one, the moon is not nearly as bright as the sun, so they are likely pretty dim to begin with and since the human eye has trouble seeing in color even in the light of a full moon I imagine moonbows would not be very visually spectacular.
I also imagine that you’d probably need to be far from city lights to see one too. The reflection of street lights on the rain clouds would probably be enough to cause the moonbow to be lost in the glare in most cases.
Moonbows exist, but because the moon is dimmer than the sun and your eye is responding more with rods (which see black and white) than cones (color vision) they tend to be colorless. See M. Minnaert’s classic text “The Nature of Light and Color in the Open Air”, published now by Dover books. I think there’s probably something on it in Robert Greenler’s book “Rainbows, Halos, and Glories”. And, of course, you can always find something on such esoterica in my standard fallback, Jearl D. Walker’s “Flying Circus of Physics”
I’ve seen a moonbow. It was absolutely amazing. It was a slightly damp, somewhat cool evening and there was a full moon. A HUGE ring was around it with the moon at the centre and I mean huge… you could probably put 10 moons between the one at the centre and the moonbow ring. As was said in previous posts, it was mostly monochrome, maybe some very muted reds and violets. We stared at it for hours.
Arken:
What you describe CAN’T be a moonbow. It’s a lunar halo.There are lunar holas at about 22 and 46 degrees away from the moon. The lunar rainbow, or moonbow, however, is 42 degrees from the anti-lunar point (the point in the sky OPPOSITE the moon). Since this spot is underground (unless you’re on a mountain or above a waterfall or up in a plane) you can’t see a complete circle for a moonbow. Besides, you’re looking AWAY from the moon to se it – not TOWARD the moon.
I’ve seen the waterfall circular moonbow at the Victoria Falls in the Zambezie River. The falls plumet between walls of stone, and the mist is continuous.
I would guess that the color shift is partly due to the reduced light, so that most of your impression is based on the retina’s rods rather than the cones.
You can only see a rainbow if your back is to the sun. So does your back have to be to the moon too?
Handy:
Yup. See my post above.
Actually you COUL always face the moon – if you’re looking in a mirror.
CalMeacham, if you look at a rainbow when you are in a plane, its a full circle. cool.
Nuh-uh! A least a bit of it has to be cut off, right?
I have seen lunar halos on several occasions, and saw a moonbow once. I was driving home from a night shift, was out in the country, on a night with a very bright full moon. It looked exactly like a rainbow except that it was faint and just appeared to be lighter and darker bands. It was barely perceptible if you looked directly at it, but stood out quite clearly if you looked just away so that the peripheral vision picked it up. It was really rather unremarkable looking, but I thought it was extremely cool because it was such a shock to see it. I had never heard of them before, nor even given the idea of a moonbow a thought.
Handy and scratch:
In principle, if you’re high enough you ought to be able to see a complete circle rainbow if you’re up in an airplane. I have a sketch showing this in a 1942 book called “Wonders of Science Simplified”. Unfortunately, that book is full of errors – and their sketch isn’t entirely accurate. Still, it’s possible. You’ve got to be able to see 42 degrees below you – and it dioesn’t matter if it’s below the horizon. The problem is that you have to have water droplets at all the angles, and that’s rough. (A cheap way to see a 360 degree rainbow is to make one using your garden hose).
You might be confusing a rainbow with the GLORY. I see glories very often when I’m up in a plane. It’s a very tight rainbow-like circle that completely surrounds the shadow of the plane thrown onto a cloud. It’s almost always a complete circle. It’s not a rainbow, though. The reflection and refraction responsible take a different path through the raindrop. Before airplanes were around the only way you could see one of these was to go up on a mountaintop and look at your shadow cast on the morning fog down in the valley. You’d see a multicolored halo around your head. This phenomenon was sometimes called “The Spectre of the Brocken”, and it’s covered in the books I cite above.
CalMeacham wrote:
So is a Lunar Halo a similar effect? It looked EXACTLY like a rainbow except it was a complete circle and the colours were so muted that it was almost greyscale.
If you get the sun at the right angle (make that the “correct” angle) you can turn around in a circle, making a rainbow around your body.
**
Cool. I’ve heard that this was the case, but I’ve never heard of anybody who specifically saw this. I’m jealous.
I have also seen partial rainbows from airplanes, but never the whole circle.
When I was in Springfield Oregon this spring I saw a rainbow so vivid that I could clearly see the secondary rainbow for a minute or two. It was amazing and I wish I could have taken a picture. I did take a picture of one I saw in Ketchikan, Alaska, but it didn’t come out as vividly as I would have liked.
Arken:
The smaller lunar halo is due to refraction of the light both as it enters the droplet and as it leaves it. (I can’t recall right now the cause of the larger halo – and my books are at home.)A rainbow (or a moonbow) is the result of light refracting as it enters the droplet, reflecting once off the back of the drop, then refracting again on its way out. A secondary rainbow (as Latecomer describes) is due to rays that bounce TWICE inside the droplet before exiting (they’re not that rare – I’ve seen lots of 'em). You could, in principle, have third-order and fourth-order rainbows (with three and four internal bounces, respectively), but a.) the light gets dimmer with each reflection and b.) the third and fourth order bows are too close to the sun. There was a really neat article by Jearl Walker in, I think, American Journal of Physics about twenty years ago that gave a color diagram of all the different order rainbows.(Note that the halo is, in effect, a zero-order rainbow, since there’s no internal reflection. A halo is a cousin to the rainbow, but not the same thing)
Another good source is R.A.R. Tricker’s Introduction to Meteorological Optics. It’s got mathematical treatments of these, but they’re understandable. For the masochistic, there’s van de Hulst’s “Light Scattering by Small Particles”.