From myth to reality: Photos prove triple rainbows exist

Oct 05, 2011

Few people have ever claimed to see three rainbows arcing through the sky at once. In fact, scientific reports of these phenomena, called tertiary rainbows, were so rare—only five in 250 years—that until now many scientists believed sightings were as fanciful as Leprechaun's gold at a rainbow's end. These legendary optical rarities, caused by three reflections of each light ray within a raindrop, have finally been confirmed, thanks to photographic perseverance and a new meteorological model that provides the scientific underpinnings to find them. The work is described in a series of papers in a special issue published this week in the Optical Society's (OSA) journal Applied Optics.

In addition to the confirmed photo of a tertiary rainbow, the optical treasure hunt went one step further, as revealed in another photo that shows the shimmering trace of a fourth (quaternary) rainbow.

Raymond Lee, a professor of meteorology at the U.S. Naval Academy, did not snap those pictures, but he did make them possible. One year ago, Lee predicted how tertiary rainbows might appear and challenged rainbow chasers to find them.

Although staggeringly rare, tertiary and quaternary rainbows are natural products of the combination of refraction, dispersion, and reflection inside raindrops. These are the same processes that create all rainbows, yet they are taken to their most extreme to produce these higher order variants. Refraction is when sunlight bends as it moves from air into water and vice versa. (Such bending makes oars look bent when partially submerged.) Water droplets bend each of the colors in sunlight by a slightly different angle. This is called dispersion, and it separates the colors to create a rainbow.

Most of that multicolored light passes through the other side of the raindrop, but some is reflected. The raindrop's spherical curves concentrate those reflections at 138 degrees from the Sun. This concentrated light is bright enough to create a visible primary rainbow.

A double rainbow occurs because not all that light exits the raindrop. Some is reflected back into the raindrop and goes through the whole process again. Although this light is dimmer, sometimes it is bright enough to produce a secondary rainbow just outside the first.

A third series of reflections creates a tertiary rainbow. It is even dimmer than the secondary rainbow, and much harder to find because instead of forming away from the Sun, a tertiary rainbow forms around the Sun. To see it, observers have to look into the Sun's glare.

This may be why only five scientifically knowledgeable observers had described tertiary rainbows during the past 250 years.

Lee reviewed each description. He eliminated one questionable account and found common elements in the others. All described tertiary rainbows that appeared for a few seconds against a dark background of clouds about 40 degrees from a brightly shining sun.

Along with colleague Philip Laven, Lee used a mathematical model to predict what conditions might produce visible tertiaries. First, they needed dark thunderclouds and either a heavy downpour or a rainstorm with nearly uniformly sized droplets. Under these conditions, if the Sun broke through the clouds, it could project a tertiary rainbow against the dark clouds nearby. The contrasting colors would make the dim tertiary visible.

When Lee presented his findings at last year's International Conference on Atmospheric Optics, it sparked heated discussion. Some scientists insisted that past descriptions were wrong and that tertiaries were too dim to see in the Sun's glare.

One attendee, Elmar Schmidt, an astronomer at Germany's SRH University of Applied Sciences in Heidelberg and a rainbow chaser, took the guidelines as a challenge. He alerted likeminded amateurs. Since then, Michael Grossman and Michael Theusner have snapped photos of tertiary rainbows. One photo even shows a quaternary rainbow, and both images, which underwent only minimal image processing to improve the contrast under these challenging photographic conditions, appear in the same Applied Optics special issue as Lee and Laven's paper.

The day Grossman photographed the tertiary rainbow, he first recalled seeing a double rainbow. When the rain intensified, he knew he had to turn toward the Sun. "It is really exaggerated to say that I saw it, but there seemed to be something," he says. The pictures he snapped in the rain were the first to show a tertiary rainbow.

Of the noteworthy discovery, "it was as exciting as finding a new species," Lee says.

Explore further: Scientists discover novel metamaterial properties within hexagonal boron nitride

More information: Papers:

Visibility of natural tertiary rainbows, Raymond L. Lee, Jr. and Philip Laven, Applied Optics, Vol. 50, Issue 28, pp. F152-F161 (2011)

Photographic evidence for the third-order rainbow, Michael Grossmann, Elmar Schmidt, and Alexander Haussmann, Applied Optics, Vol. 50, Issue 28, pp. F134-F141 (2011)

Photographic observation of a natural fourth-order rainbow, Michael Theusner, Applied Optics, Vol. 50, Issue 28, pp. F129-F133 (2011)

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User comments : 13

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Digi
5 / 5 (14) Oct 05, 2011
A picture paints a thousand words. This article needs to be a thousand words longer.
Shabs42
5 / 5 (4) Oct 05, 2011
Photos in the original article, but they aren't very clear which probably explains why they were left out here.

http://www.osa.or...ist.aspx
bluehigh
1 / 5 (1) Oct 05, 2011
So very pleasing. Having seen a triple rainbow looking south across farmland (canola crops mostly) at Bathurst, NSW. I have for some years been perplexed to read that according to 'authoritative sources' such a sight is not possible. Whatever the optics involved, I know it happens. Lucky I am to have seen such a supposedly rare event.

Skultch
3 / 5 (2) Oct 05, 2011
I thought I had seen a triple on two different occasions, but it turns out that they were both a double and a supernumerary. The wiki says a supernumerary has pastel colors, but what I saw were definitely primary colors and the order was reversed, which made it look like the rainbow had been copied then folded back right. Kinda hard to explain. The order was: ROYGBIVVIBGYOR for the main rainbow, then a normal double.
anthonys
not rated yet Oct 05, 2011
Thomas Baines painted a well-known painting of Victoria Falls with a triple rainbow approx 150 years ago. Obviously the heavy spray from the waterfall created the conditions necessary to cause the three annular rainbows around the sun.
Seems as if people are knowing more and more about less and less.
rawa1
2.5 / 5 (2) Oct 05, 2011
Light from the primary bow gets bent through 137.5 degrees, light from the secondary bow gets bent 231 degrees. Since we look opposite the sun (180 degrees away) to see a rainbow, the primary bow has a radius of 180 - 137.5 = 42.5 degrees and the secondary bow has a radius of 231 - 180 = 51 degrees. That's why they appear close together. Light from the tertiary bow gets bent 317.5 degrees, so the bow is only 42.5 degrees from the sun. It's in a completely different part of the sky.

http://www.busine...sLang=en

To see a tertiary bow, you'd have to be looking through rain toward the sun, and there's a lot of glare in that direction. To make matters worse, the fourth order bow overlaps the third order bow but with reversed colours, meaning anything you do see will be washed out.
rawa1
1 / 5 (7) Oct 05, 2011
IMO The dispersion of light with droplets into rainbows could have an analogy in dense aether model, because the dispersion of light with water droplets in rainbows should correspond the dispersion of light with subtle density fluctuations of vacuum (CMBR noise).

http://aetherwave...les.html

The so-called Alexander's dark band between primary and secondary rainbow correspond the empty dark cosmic space, where we are living in. The surface of (particles of) matter could correspond the primary rainbow, the surface of antimatter the secondary rainbow. There were already attempts to explain the geometry of space-time with dispersion of light with metamaterials - so that the mainstream physics is aware of this connection too in certain extent.

http://www.physor...601.html
that_guy
4.4 / 5 (7) Oct 05, 2011
Triple Rainbow! What does this mean! Oh my god, it's so beautiful....(etc).

I wish they had posted pictures too. I found some on google pretty easily. It's interesting how the first two rainbows are usually parallel, but the third rainbow almost always crosses at an angle between them.

I wonder how much of their research involved googling "triple rainbow".

http://www.indian...nbow.jpg

Here are a couple I found. They're really cool.

Here's an interesting one...
http://suddenoakl...bow2.jpg
Callippo
5 / 5 (1) Oct 05, 2011
Here are a couple I found. They're really cool.
They appear cool, they aren't true triple rainbow, which this article is about. Multiple rainbows result from reflection of sunlight from large water surfaces beneath horizon. They appear in random angles and positions with respect to main rainbow.
Chef
5 / 5 (2) Oct 05, 2011
"a tertiary rainbow forms around the Sun"

Sorry, but this not always the case. I have witnessed a tertiary rainbow before, and I was not looking toward the sun. In fact there were 5 distinct rainbows in the sky at the same time. Two were very vivid, with a third right along side them in the same arc, but dim, and then there was a gap (about a fist size at arms length), and then two more rainbows fairly high above the others. To this day I wish I had a camera then to capture the image.
Nanobanano
5 / 5 (1) Oct 06, 2011
I've seen at least 3 DOUBLE rainbows that I can remember.

I don't think any of them were triples, but it might just be a matter of looking at the right time and from the right angle.

I know I've seen a photograph on the internet of a "triple double" rainbow, where the reflections of the rainbow were bouncing off a lake, creating a total of 6 rainbows.

I found a link to it at NASA, but the link doesnt work.

I also found a like to an alleged quadruple rainbow online, but it is in a waterfall, so that probably doesn't count.
DrSki
5 / 5 (1) Oct 06, 2011
As with waterfalls, the density of the water droplets is not uniform, and given that the light-source is penetrating multiple layers, separate PRIMARY rainbows occur and can explain triple rainbows. (Like the one my daughter took a picture of last Friday). Additionally this would help explain QUAD bows as two primaries.

Occam's Razor

Has anyone seen the DOUBLE 'Moonbow' in the falls at Lake Cumberland in Kentucky (USA). I've only seen pictures.
that_guy
not rated yet Oct 06, 2011
@ callipo - I think you're right that they are talking about a triple/quadruple rainbow from the same refraction source, instead of independant rainbows.

@Nano - Probably many more. I know I don't remember all the double rainbows I've seen, but I recall that they seem pretty common from Hawaii or the coasts. I almost never see rainbows now that I live in the desert.

@DrSki - I have a picture of a double moonbow on my FB :). Apparantly what we lack for rainbows in the desert we make up with moonbows. It was very cool - I was at a friend's house and walked out to smoke - Then i called everyone outside.

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