Talk:Rainbow

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Rainbow is a former featured article. Please see the links under Article Milestones below for its original nomination page (for older articles, check the nomination archive) and why it was removed.

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January 19, 2004	Featured article candidate	Promoted
January 21, 2006	Featured article review	Kept
February 11, 2007	Featured article review	Demoted
Current Status: Former featured article

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[edit] older entries

The following article was copied from an E-newsletter for the New Mexico Academy of Healing Arts:

/ Why you can never see the end of a rainbow? It doesn’t have one. Theoretically, the light continues to bend into a complete circle—a circle we can’t see because it is cut off by the horizon.

Most people know the colors of the rainbow: red, orange, yellow, green, blue, indigo, violet. But few have been fortunate enough to see some of the rare manifestations of this natural phenomenon. Some rainbows are all purple, all red or even all white. Purple rainbows are only seen before or at sunrise. They can be formed by high clouds that scatter the blue and violet light, which raindrops reflect back to the observer. At sunset, when the sun is low in the sky, a rainbow may be a dramatic red arc, because the shorter wavelengths (blue, green and yellow) have been dispersed during their relatively long trip through the atmosphere.

White rainbows can appear in daylight or moonlight, but for entirely different reasons. During the day, rays of sunlight may be reflected from very small droplets of moisture—so small that the emerging bands of color are close enough to overlap, creating white light. But a white rainbow seen by moonlight is not white at all. It only seems so because the eye cannot detect color in light as weak as what the moon is reflecting. However, a photograph of a lunar rainbow, taken at the correct exposure, will be full in color.

The "rainbow" article should address some of the other colored rainbows that, though, rare, can happen from time to time.

Last night I saw the strangest and maybe the most rare form of rainbow. I have never heard of this but I can only describe it as a black rainbow. It was late in the evening and the sun was far below the horizon. The light was a very deep red and reflecting off of the clouds. In the east against a dark background of clouds appeared a very faint purple rainbow. I guess, since only red light was present, the resulting spectrum appeared only purple. Has anyone else seen one of these? How can I find out more?

Very nice diagrams of refraction (with the red lines). Very good at explaining the phenomenon.

---

I think that a rainbow is visible only when the sun is at a low altitude- mornings and late afternoon/ evenings. Isn't there some specific angle for this? KRS 15:33, 1 Feb 2004 (UTC)

I added: Hence there is no rainbow if the sun is at a higher altitude than 42°: the rainbow would be below the horizon. --Patrick 23:30, 1 Feb 2004 (UTC)

Nevertheless, it is not true, as sometimes one can look below the horizon. For example, if you are looking down from a mountain, or - as mentioned in the article! - from an aeroplane.

I've deleted the incorrect reference to glories from the aeroplane comment. Glory is a different optical phenomenon from rainbow and it is incorrect to state that a full-circle rainbow is a glory. This error needs to be removed from the page Glory_(rainbow) and I've put that on my task list, but I'm not sure how to fix the problem that the error is incorporated into the page title. Advice welcome. --Richard Jones 13:45, 20 Mar 2004 (UTC)

I've moved it to Glory (optical phenomenon). ––wwoods 18:12, 21 Mar 2004 (UTC)

Added: Even more rarely is a triple rainbow seen and a few observers have reported seeing quadruple rainbows in which a dim outermost arc had a rippling and pulsating appearance. - Sounds fantanstic, but I saw this, and I was not the only one - Leonard G. 03:50, 25 Aug 2004 (UTC)

[edit] Angle derivation

The article does a clumsy job about what is special about the 42° or the 52° angle. The picture lead me to correctly see that light can be refracted-internally.reflected-refracted.again at a large range of angles, its just that 42° is where the largest intensity of refraction occurs. The page http://www.phy.ntnu.edu.tw/java/Rainbow/rainbow.html has a much better explanation for the angle. 129.42.208.182 21:46, 30 Aug 2004 (UTC)

Yes, I agree with the comment offered above: I think the crucial part of the linked article is where it says "The rainbow is actually a disk of scattered light, but it is brightest at the edge; the disk for different wavelengths is a different size, and that is why we see the color effects there." In other words, the difference between the rainbow and a pure spectrum made by a prism lit from a slit is this: In the prismatic spectrum, each color has just one line position (if the slit is narrow), and the result of adding all those together is a sequence of approximately pure colors. But in the rainbow, each color has not so much a line, but rather an arc of light, with some thickness, it is brightest at its outer edge, but it also has brightness at distances away from that outer edge, fading away inwardly as one gets farther from the edge. So the rainbow color palette results from superimposing all those bright colored edges along with their adjacent areas of fading intensity for each color. This makes the resulting rainbow colors actually impure, compared with pure spectral colors resulting from a slit and prism. Another way to visualize this is to think of the rainbow as a chromatically-dispersed caustic: A caustic is like the curve of light that can be seen on the surface of a cup of milky coffee when it is lit from the side -- the lighted area has a sharp bright edge, but it's not purely a bright line, it has thickness, and its brightness gradually fades away from the maximally-bright curved edge. Every spectral color makes one of those caustics, but with slightly different diameter; and when they are superimposed on each other, there you have the rainbow.

[edit] Moonbow

I'm not clear on this section: In a very few cases, a moonbow, or night-time rainbow, can be seen on strongly-moonlit nights. As human visual perception for colour in low light is poor, moonbows are perceived to be white. In Hawaii, we see moonbows all the time, and it's possible to make out many colors. So, what does the editor (or author) mean by "in a very few cases"? --Viriditas 12:00, 29 Oct 2004 (UTC)

[edit] Triple Rainbows

The article states: Even more rarely is a triple rainbow seen and a few observers have reported seeing quadruple rainbows... These things are not rare in Hawaii. I've seen triple rainbows many times and a quadruple rainbow only twice. --Viriditas 12:32, 29 Oct 2004 (UTC)

More importantly we could use a scientific explanation of how they are possible. I've seen a 3+ rainbow and know that the additional bows cannot be explained using Descartes' internal reflections in a rain drop. -- Solipsist 08:32, 24 Nov 2004 (UTC)

I have personally seen a triple-banded rainbow that looked very much like the "supernumerary" rainbow pictured in the article; the colors in the rainbow I witnessed were red, orange, yellow, green, blue, violet, green, blue, violet, green, blue, violet. When I turned around, I saw that two small dense clouds close to the sun were extremely bright (almost as if I was seeing a reflection of the sun off an icy lake). I theorize that either those two clouds acted as second 'suns' bright enough to produce two more rainbows that overlapped the one from the sun itself, and that the combination merged into one supernumerary rainbow, or else that the supernumerary bands of the rainbow became visible due to the increased intensity of the sunlight from the reflections. It is extremely unlikely that the raincloud under which I saw that rainbow was producing raindrops all of a fixed size, as some web sites propose to explain supernumerary rainbows. The primary explanation may be wave interference as Thomas Young said, but I think there must be other requirements to explain why they are rarely seen. (I reverted my first entry here before anyone replied to it, when I realized it was a foot-in-mouth mistake). Aumakua 15:57, 2 December 2005 (UTC)

Im no expert on the subject of rainbows but have on occasions observed tripple rainbows over the coast, but once, around trwenty years ago, I had observed no less than twentyfive at the same time. These were much smaller than any bows i had prieviously observed. Each seemed to occupy its onwn space and at different angles; they were also very faint and hard to count. The time of day was an evening, about 5.30pm, late winter/spring, mostly overcast and after a good rainstorm. The location was England, cromer(a coastal town on the east),direction looking north-west to north over the sea horizon. I have read only once of someone observing the same atmospheric condition but have no knowledge as to the cause of this particular phenominon or the rarity of it. Sadly no images of it though.Maybe you guys that do understand these thing could spread some light of knowledge. The only explanation i can find so far is that of supernumerary rainbows.

[edit] Mnemonics

The main mnemonic described in the article is 'Richard of York...', given the subject am I right in thinking that this is only commonly used in the UK?

Another editor has also added 'Roy G. Biv' saying it is more common. I haven't heard this one, is it common in the US? -- Solipsist 08:43, 24 Nov 2004 (UTC)

I don't know about the US, but it is common in Australian schools. - Jeff Parsons (sorry, no account yet)

Yah, it's common in der Staes Flip Merav 21 10:40, 3 June 2006 (UTC)

[edit] Total internal reflection?

The article states that light is reflected from the back of the drop under total internal reflection. I find this statement rather dubious at best. A quick derivation from snell's law shows that the minimum angle for total internal reflection in water (using n_w = 1.33) is 48.7 degrees. That would imply that the angle at the back of the droplet is greater than 90 degrees, which by inspection is not the case.
Since light would therefore leave the back of the drop refracted, would it not be impossible to see a rainbow between the observer and the sun, if the appropriate areas of the sky were unobscured?Kenneth Charles
Edit: I did some research. Light is indeed passed out the back of a droplet, but due to the fact that there is no distinct peak of emission from this spectra, it does not form a visible rainbow. However, the statement that light is totally internally reflected inside a raindrop is wrong and should be removed.

[edit] Mythology and religion

Galileo wrote a treatise on the properties of light? I'm not familiar with this at all. If no one can provide a citation, we ought to change it to Newton, who certainly did study light and color.

It perhaps should read 'Descartes treatise'. -- Solipsist 09:22, 23 Jun 2005 (UTC)

It now credits Descartes and his (unknown) predecessor Theodoric; see below. Dandrake 03:01, 11 December 2005 (UTC)

[edit] Flask experiment

In the article Theodoric of Freiburg it is described that he did experiments with spheric flasks as models for water drops. Here in the rainbow article it is reported about Descartes. Which is true? Or both? Ikar.us 2005-06-29 11:02:14 (UTC)

They both did. See for reference:

Beverly T. Lynds, About Rainbows (on Descartes)
Rom Harre, Great Scientific Experiments (ISBN 0486422631), pages 85-93: Theodoric Of Freibourg - The Causes of the Rainbow

Jondor 29 June 2005 21:56 (UTC)

[edit] reflection rainbow - a contradiction

It says: Where sunlight reflects off water before reaching the raindrops, it produces a reflection rainbow.

Then it says: A reflected rainbow is produced when light that has first been reflected inside raindrops then reflects off a body of water before reaching the observer.

So which one is it? Thanks, Ladypine 18:15, 21 January 2006 (UTC)

Reflected versus reflection. -- ALoan (Talk) 18:31, 21 January 2006 (UTC)

Thanks, I seperated the paragraph to make it clearer.Ladypine 18:34, 21 January 2006 (UTC)

[edit] Images / German article

There has been some to-ing and fro-ing on the images recently (I cut some out and replaced with ones from Commons:Rainbow).

Which of the two following should appear as the lead image:

A rainbow arches over Florida.

A complete half-circle rainbow at Lake Zurich.

the end

waterfall

Secondly, my German is not good enough to extract more information from the excellent article in German Wikipedia. If someone can help, I should be very grateful. -- ALoan (Talk) 19:01, 21 January 2006 (UTC)

Now the Florida image is again there. I think it is the least impressive of all and should be replaced by any of the others. --Ikar.us 21:46, 13 March 2006 (UTC)

I agree. User:Desmond71 keeps putting the Florida one back for some unknown reason. -- ALoan (Talk) 00:06, 20 April 2006 (UTC)

I believe the Florida image serves as a much better lead image than the current Lake Zurich image because the main focus of the Zurich image is that of a brightly lit boat in the foreground and not of the rainbow. (The rainbow appears too dark and is almost lost among an even darker background, especially when viewed on darker monitors.) The Florida image, though admittedly not the best image around, at least does a much better job of illustrating the rainbow and therefore makes for a better lead image. I have absolutely no problem with the Zurich image that User:ALoan keeps using, but I feel it should be displayed elsewhere in the article rather than as the lead image. (I have tried contacting User:ALoan about this earlier, but I don't know how to send messages directly to users hear at Wikipedia.) -- Desmond71 17:39, 8 June 2006 (UTC)

Hi, Desmond71 - it is good to hear from you at last. The easiest way to contact me is by leaving a message at User talk:ALoan (I left some messages for you at User talk:Desmond71 a while ago, but got no reply). Fortunately, I am watching this talk page too.

I'm afraid that I just don't like the Florida image very much. I see what you mean about the Geneva image being dark, with too much emphasis on the boat; on the other hand, it shows an almost-180-degreee rainbow. The "end of the rainbow" image is also quite nice (and a featured picture but the trees are a bit of a distraction. The waterfall is also not a perfect example, and none of the others at Commons:Rainbow is perfect either... -- ALoan (Talk) 13:46, 9 June 2006 (UTC)

[edit] Section needs complete rewrite

The section "Rainbows in literature" is horrible. It does not give any explanation or information about the view, the inclusion, the metaphoric usage... of rainbows in Literature. It just features some verses. How could this be descriptive of the section's title. CG 20:23, 23 February 2006 (UTC)

{{sofixit}}. Other than the instances cited, do you have any views on the "view, the inclusion, the metaphoric usage... of rainbows in Literature"?

I also think that the first image needs to be a rainbow, not a waterfall. -- ALoan (Talk) 11:48, 24 February 2006 (UTC)

Yes, but the lead image should present a very clear rainbow. In this one, the rainbow is in the background and barely noticible. CG 17:21, 24 February 2006 (UTC)

[edit] A photo of a rainbow taken from an airplane should be introduced

I have heard that rainbow looks like different when viewed from a high place - that it is not an arc in this case but rather a ring. Someone should put an effort to get a photo of a rainbow from a plane or a high mountain

It is true, the photo on this (http://www.wunderground.com/wximage/viewsingleimage.html?mode=singleimage&handle=JeffMasters&number=0) page proves it. Not sure if it can be used here, I can't find the legal mumbo-jumbo.

In general, you see a part of a circle, depending on where the water is relative to you and the sun. Being up in a plane with lots of water below you is the best way to see the whole circle, but it's not really a difference of kind, just a better viewpoint. Notice in the picture you posted that you don't see the full circle, because there's a plane in the way, and no droplets between you and the plane. The ground does the same thing, often, especially when the rain is in the distance; if it's raining where you are, you can sometimes see the rainbow extend all around you. Dicklyon 19:25, 26 July 2006 (UTC)

Yeah, but there's an explanation about the image, and it's the best I could find. --DragonSparke 19:52, 26 July 2006 (UTC)

[edit] The end of a rainbow

The article contradicts itself, in the Rainbows in religion and mythology section it says, "The Irish leprechaun's secret hiding place for his crock of gold is usually said to be at the end of the rainbow (which is impossible to reach)." and yet, right next to it shows a photo [1] which shows the end of a rainbow. Someone should fix this or tell me why I'm wrong ;) WikiSlasher 12:01, 15 June 2006 (UTC)

You can see the end of the rainbow (or, at least, in general terms, roughly where it ends) but please let us know how you get on in reaching it... -- ALoan (Talk) 14:13, 15 June 2006 (UTC)

OK I'll admit...I haven't tried reaching it, I guess it might move a bit as you approach it, I don't know because I haven't tried it, but it seemed like a contradiction so I just thought I'd get that cleared up. Perhaps if you use a long stick to reach it that'd help! :) WikiSlasher 13:32, 16 June 2006 (UTC)

Rainbows are actually a ring, but this is only evident when you see the rainbow from above the ground, from the land, it appears as an arc. So, really, there IS no end to the rainbow. If you chase that pot of gold, you'll never reach it, and get VERY dizzy. Hope this helps clear it up. ^^ --DragonSparke 17:39, 26 July 2006 (UTC)

It is easiest to practice reaching the end of the rainbow using a small example in your back yard. Choose a sunny summer evening and set up a sprinker or hose to give a fine spray of mist. Then stand between the sprinker and the sun with your back to the sun. You should be able to see a rainbow that appears to be just a couple of meters across, but you will still have fun trying to reach the end where it touches the ground... -- Solipsist 17:12, 11 August 2006 (UTC)

There is a magnificent image of a fully circular primary rainbow at http://www.roddyscheer.com/photo_detail.php?photo=913. I presume that this image was taken from a hang glider. As the image belongs to professional photographer (Roddy Scheer), the image must NOT be added to this Wikipedia entry - but a link could be permissible.

[edit] Culture

"CULTURE" -- A small comment but from my perspective as an anthropologist, important. The heading "rainbows in mythology and religion" is in the current form separate from "rainbows in culture"; and the "rainbows in culture" includes literature and art. This implies that non-literate peoples, or religion, or mythical beliefs are not part of "culture" (or more ironically, that culture is not inclusive of myth!). More specifically, this structure of headings seems to reify the use of the term "culture" to mean something like "I got culture because I go to the opera" as opposed to culture as the full behavioral repertoire of our species, etc. I'm sure none of the darker side of what is implied in my comment (racism, ethnocentrism, etc.) is intended at all! And it is a simple fix, just use "rainbows in culture" as the main heading and subsume myth, religion, literature, etc. under that heading. --Greg Laden

Good idea. So just fix it instead of pontificating about it. Dicklyon 19:35, 19 June 2006 (UTC)

[edit] Indigo

I've removed the sentence in the mnemonics section suggesting indigo is not regarded as a colour of the rainbow, and also re-added it to the introduction. Using a simple google search seems to reveal that most sources still list Indigo, as do all the mnemonics actually mentioned:

Search for rainbow "red orange yellow green blue violet"

http://www.google.com/search?num=100&hl=en&lr=&safe=off&q=rainbow+%22red+orange+yellow+green+blue+violet%22&btnG=Search

497 results.

Search for rainbow "red orange yellow green blue indigo violet"

http://www.google.com/search?num=100&hl=en&lr=&safe=off&q=rainbow+%22red+orange+yellow+green+blue+indigo+violet%22&btnG=Search

12,200 results.

I believe these searches reveal all instances of the colours appearing in those orders, with or without commas and other punctuation in between.

Cheers — SteveRwanda 12:59, 11 August 2006 (UTC)

I think you're missing the point. Yes, it is conventional to include indigo in the sequence. But who do you know who can identify the color indigo? Or who can see a stripe of rainbow between blue and violet? The passage you removed captured the relationship between the conventional sequence mnemonics and the actual perception pretty well and neutrally, I thought. Dicklyon 16:54, 11 August 2006 (UTC)

Can you provide a citation for the paragraph (i.e. that humans are not able to perceive indigo)? -- ALoan (Talk) 17:01, 11 August 2006 (UTC)

Contemporary Color: Theory & Use, by Steven Bleicher, p.6 [2] says "However, most people can only discern six of these hues; they have trouble telling the difference between indigo and violet." Dicklyon 04:23, 14 August 2006 (UTC)

Excellent - please would you add the citation to the paragraph so the next time someone questions it, they can see the source for our assertion. -- ALoan (Talk) 11:03, 14 August 2006 (UTC)

I've now added that citation in the relevant spot. Just for the record, I wasn't questioning whether humans can see indigo in a rainbow, merely whether modern definitions always omit it, as the previous paragraph seemed to imply. I believe it's now more accurate and informative! Cheers — SteveRwanda 18:10, 15 August 2006 (UTC)

OK, point taken. I've restored the paragraph, though without the sentence most modern rainbow definitions do not include that as a distinct colour which I regard as untrue. It's kind of a repetition of what it says about indigo in the intro, but maybe that's the correct style for articles anyway - i.e. the intro is a summary of points in the article itself. Cheers — SteveRwanda 19:16, 11 August 2006 (UTC)

I have read an academic paper in which the author claimed that s/he had examined Newton's notebooks and worked out the wavelengths of the seven colours. This showed that what Newton called "indigo", we today would call "blue", and what Newton called "blue", we today would call "blue-green" or "turquoise". I've added an appropriate comment to the page. However, I have been unable to relocate that academic paper: I'll keep looking. — Neil Dodgson 12:05, 8 February 2007 (UTC)

[edit] Finally some decent photos

Thanks, Ceinturion, for the two new lead photos. Dicklyon 22:36, 26 August 2006 (UTC)

I am really glad that maker of the first lead photo (Eric Rolph) agreed to upload it to wikipedia. Ceinturion 22:02, 28 August 2006 (UTC)

One problem with that image is that its licensing is currently contradictory. The permission line inlucdes 'NonCommercial' and 'NoDerivs' which suggests that it should really be licensed as cc-by-nc-nd which is no longer an accepted license on Wikipedia. -- Solipsist 13:02, 1 October 2006 (UTC)

The history shows that he added the {{cc-by-sa-2.5}} license in a separate edit AFTER the "non commercial no derivs" initial license, so I would presume that license supercedes and we're OK. Dicklyon 19:14, 1 October 2006 (UTC)

Someone still ought to ask them to fix the licensing. -- Solipsist 16:26, 2 October 2006 (UTC)

It's hard to ask inactive User:Ericrolph anything. No user page, no talk page, no recent contributions. But give it a try, in case he logs in. Dicklyon 17:16, 2 October 2006 (UTC)

[edit] Redundant image of double rainbow

The new image of a double rainbow (Double_rainbow_2.jpg) does not really add anything compared to the existing image of a double rainbow (Regenbogen_NASA.jpg). Therefore I would like to remove the new image next week, but I don't want to offend the person who submitted it. If you think the new image is better than the old one, please explain it here. Ceinturion 22:02, 28 August 2006 (UTC)

[edit] My Rainbow

This seems to be the place to dump rainbow pics so here's mine. This one show's how close to the ground they can get. This one is hugging the hillside less than 15 feet away.--God Ω War 03:04, 29 August 2006 (UTC)

But there's no garage door in the picture. What's up with that? Dicklyon 03:45, 29 August 2006 (UTC)

[edit] ROYGBIV

The convention of seeing red, orange, yellow, green, blue... is not universal. Different cultures see the color breaks at different places. 67.120.92.193 01:34, 2 January 2007 (UTC)

Also, it isn't particular to rainbows. Don't merge. Melchoir 00:08, 24 January 2007 (UTC)

Close for lack of support even by the originator. Dicklyon 02:37, 24 January 2007 (UTC)

[edit] Why does the rainbow form an arc across the sky?

Scientific explanation of why the rainbow forms an arc would be a great addition to this page. Its the question I'm still left asking. Agelena 17:46, 25 February 2007 (UTC)

The rainbow forms at a constant angle from the direction that the sun is going. That makes it a circle. But you only get the part of the circle where there are raindrops in the sunlight. Dicklyon 17:53, 25 February 2007 (UTC)

Saying the same thing: It's the 40°–42° mentioned in the article -- wherever there are water droplets at an angle of 40° from you (as you are looking away from the sun), you'll see a spectrum. The set of positions which are 40° away from you are a circle (40° straight up, 40° to your right, 40° halfway-between-straight-up-and-to-your-right, and so on). (If I could write this more clearly, I'd add it to the main page :-) Hope that helps. not-just-yeti 18:00, 25 February 2007 (UTC)

Here's a good illustration I found on this page. Dicklyon 21:53, 25 February 2007 (UTC)

[edit] holaaa

la verdadd q nda mas kieroo buscar el significadoo de los colores del arco9iriss y qeste escrito en ingles —The preceding unsigned comment was added by 200.89.162.178 (talk) 21:33, 7 April 2007 (UTC).

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