Cause of the Long Island Quadruple Rainbow

April 21st, 2015 by Roy W. Spencer, Ph. D.

The media has been buzzing about an unusual photo taken on Long Island this morning, from a commuter train at the Glen Cove station, of what appeared to be a quadruple rainbow. Being a meteorologist and having a website that answers questions like “What Causes Rainbows?”, I have more than a passing interest in this.

I’ll admit, I had never seen such a thing before, captured by Amanda Curtis and posted on Twitter:
quadruplerainbow

While at first I figured this was a hoax of some sort, there were multiple reports and photos of this event, and I found even more photos (but not many) on the internet of similar quadruple rainbows, e.g. this one from Reddit.com:
quadruple-rainbow

Now, most people have seen double rainbows, which are basically concentric segments of two halos opposite the sun, when the sun is low in the sky, created by refraction of sunlight through raindrops.

What is unique about these sightings is that there are TWO sets of double halos…but with different centers, which means (in effect) from “two suns”.

So, what could cause this? Well, the two suns on Tatooine from the original Star Wars movie would do it:
2011-09-22-tatooine-e1397085055201

OR…it can be caused by reflection of the sun off a water body providing a second “sun”, which then provides the additional point source of light for the second set of rainbows.

Note that the two examples above were close to water bodies (Long Island in the first photo, and then the unknown coastal location in the second).

I did a quick search online and could not find a similar explanation, but it is the only immediately obvious one that I can envision. Maybe readers here have more information.


51 Responses to “Cause of the Long Island Quadruple Rainbow”

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  1. Mike Bromley says:

    Climate Change.

    Oops……

  2. John Smith says:

    the cause?
    in the 21st century it’s ‘climate change’ or humankind’s sinful efforts to stay warm
    in the 15th century it was the Devil

    • Lewis says:

      Dear Mr. J. Smith,

      Please explain the difference. The point being that those who shout “climate change” are willing to sacrifice others, if only indirectly, to satisfy the god’s of their belief, while historically, sacrifices were more entertaining.

      When the Red Queen Ruled.

  3. Philip Thackray says:

    The bright inner and bright outer (reversed) rainbows 1,2 and the dull inner and dull outer (reversed) rainbows 3,4 suggest a reflected source for rainbows 3,4. Also, it seems that rainbows 3 and 4 appear above the primary rainbows suggesting a lower source for rainbows 3 and 4.
    Phil

    • Slipstick says:

      I didn’t notice the reversal. That would make reflection the more likely source.

    • Joel Shore says:

      Nope…The reversal of the colors is not due to a reflected source. It is well-known that the secondary rainbow has reverse colors from the primary. The secondary is due to two reflections, rather than one reflection, inside the drop…Nothing to do with the source.

      Also, the fact that the secondary is above the primary is also expected.

      It would be rainbows #2 and 4 that are the puzzles…and could be due to light that comes from a reflection off of the water, as Dr. Spencer has suggested. It seems to me, however, that the water causing this reflection has to be sort of localized, as does the rain producing the bow, in such a way, that the reflected light from the sun ends up coming from a well-defined direction rather than a whole range of directions. (But my 3-D visualization skills are not great, so I could be mistaken.)

  4. Slipstick says:

    It could be two double rainbows created by close but separate sheets of rain, the separation orthogonal to the LOS causing the rainbows. Just a thought.

    • it doesn’t matter how many sheets of rain are involved or their orientation; with a single source of light, there will be a single rainbow (or concentric double rainbow) from a single observer’s position.

  5. Ovi says:

    Could it be due to the picture being taken thru the glass window of the train. Possibly something to do with refraction and the location of the photographer and reflection inside the lens system.

    I vaguely recall some strange effects when shooting close to the sun, due to reflections in the lens system.

  6. Possibly a double rainbow photographed through double glazing.

    I have often see a secondary image of the sun or moon when looking through double glazing at certain angles.

  7. stevek says:

    You see that the two fainter rainbows have same color ordering, opposite that of two stronger rainbows.

  8. jimc says:

    Since the pairs are both nearly semi-circular, the sun must be near the horizon. The water reflection seems very plausible.

  9. Kasuha says:

    Sun’s reflection off water is my guess, too. Provided there was enough water in direction towards the sun at the place where the rainbow appeared.

  10. Slipstick says:

    Immediately after posting about the reflection, I recalled that the double rainbow is caused by internal reflections in the raindrops and the inversion is a consequence of that. I will return to my original suggestion of two sheets of rain. A rainbow is visible over an angular range, although it is only a few degrees, so that it is possible that two separate sheets of rain, if they were not quite parallel, could produce two double rainbows with the appearance of differing point sources. I’m not sure about the double glazing effect on photography in this case; the light from a rainbow is not very intense. Also, referring to the first photograph, if it was due to double glazing, either the shadow of the tree would be visible in the foreground bow or the tree would be overlaid by the bow. A fascinating puzzle. Thank you, Doctor.

    • Jonathan says:

      As a reflector of light, rain is neither a point source nor a planar source, but a cloud of point sources (where each raindrop is a point). The concept of a “sheet” of rain is a misunderstanding; the reflection comes from multiple raindrops throughout the rainfall area, not the near edge of the rainfall area.

      As light is reflected and refracted by the raindrops, each frequency of light will be refracted at a specific angle. With the light source behind the observer, red will always appear at the same angle, regardless of the position of the raindrop, the light source, or the observer. The field of view of the rainbow will always be the same, with the center of the rainbow being in line with the observer and the light source.

      When a secondary rainbow with an offset center appears, as is pictured, there MUST be a secondary light source. This secondary light source will be in line with the observer and the center of the secondary rainbow.

  11. Hifast says:

    Roy,

    Today’s photo is from the Glen Cove LI RR station which has a body of water just east of it (actually a water hazard/pond in a golf course). Your explanation is perfect.

    The arcs intersect at the horizon meaning the sun, its reflection and obserer/photographer are all on the same line.

    What a fun puzzle of physics!

  12. MarkB says:

    The Wikipedia page has a pretty good explanation of the classic double rainbow and the “reflection rainbow”. Per the article the classic double rainbow (the concentric pairs per Dr Spencer’s description) are the product of a single and double reflection within the raindrops. The double reflection rainbow has the color order reversed as stevek observes above.

    The other pair is a “reflection rainbow” produced by the reflection of the sun off the water surface as Dr Spencer explained. The primary and “reflection rainbow” have the characteristic of intersecting at the horizon.

    http://en.wikipedia.org/wiki/Rainbow#Reflected_rainbow.2C_reflection_rainbow

    • Roy Spencer says:

      Good find, Mark! I didn’t think of checking Wikipedia. DOH!

    • KevinK says:

      Yes, MarkB has it correct, single light source, both reflection and refraction rainbows. Proof is the color reversal between the two sets.

      You can actually model the optical characteristics of a rainbow with modern optical ray tracing software. Zemax (trademark) is one program that does this. At one time you could download a free demo version and there was a sample “lens design” file on their website that shows how a rainbow works.

      Cheers, KevinK

    • Joel Shore says:

      Cool…And, I take back my first thought that the water body might need to be quite small; I guess if the surface is really smooth enough, it could be extended and there would still be a nice specular reflection at a well-defined angle.

    • Joel Shore says:

      That Wikipedia page is also quite good because it explains a rainbow well enough to understand how it is a (colored) caustic. A pet peeve I have with lots of rainbow explanations, like the one-paragraph one that Dr. Spencer linked to, is that they show it by drawing a single ray of light entering the drop at one location. This glosses over the whole fact that rays entering the drops at other locations (relative to the axis of the drop) will end up coming out at other angles and hence oversimplifies the actual phenomenon.

      In the Reddit photo, one can clearly see the caustic nature of the rainbow, with the area inside the inner bow(s) being brighter than the area outside.

  13. ossqss says:

    Shooting a picture through dual pane insulated glass?

  14. stevek says:

    if this is not an illusion it is quite amazing as look how strong the two brighter ones are. In the other photo the bows sharing same base have one strong bow and one weak bow. This photo two bows sharing same base appear about equally strong. That would seem odd for reflected bow off water body to be so strong but I imagine a possibility.

  15. Norman says:

    What about photoshop?

    • Roy Spencer says:

      Photoshop and refraction through the window were my first guesses, quickly rejected….but MarkB above found the Wikipedia support. A “reflection rainbow”, with the cause as I guessed.

      • JohnKl says:

        Hi Roy,

        The 2nd photo showing trees, a body of water and a person standing near the edge appears very similar to the “reflection rainbow” MarkB referenced. However, the 1st photo with blue sky, telephone/power lines and multiple rainbows looks photo-shopped or like plain fakes to me. Thanks and…

        Have a great day!

    • Slipstick says:

      Possible, but why bother?

  16. geran says:

    Let’s not be too quick to rule out the second sun theory….

    🙂

  17. Slipstick says:

    I’m developing a new theory to explain the double-double rainbow. It will also explain why objects in a mirror appear reversed horizontally but not vertically and why batteries are depleted in an unused flashlight. The paper will be peer-reviewed, that is if you consider a domestic short-hair cat a peer, and will feature a veritable cornucopia of Wikipedia citations. I’m calling the theory “light creep”. (Apologies to all. I couldn’t resist.)

  18. Patrick Ellul says:

    They also both early in the morning (low sun) with cloudy skies; maybe the reflection of the sun isbounced from under the clouds…

  19. nutso fasst says:

    NOAA scientist and avid photographer Paul Neiman says it’s a reflection from a smooth water surface behind the viewer, which is what we see in the second example above.

    http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=2963

  20. Peter Shaw says:

    Reflection from a horizontal surface would (notionally) produce two circular rainbows, intersecting at the horizon – which seems the case.
    While the rainbow image is at infinity (well, 1.5E11 m), its true distance and width depends on how close and dense the rain is. The reflecting surface must be of comparable width. The bow width varies with the “sun”, so I think the scenario is a small area of flat water in front of the observer, and a close, dense shower of rain.
    Low-angle reflection polarises light strongly; so does the rainbow refraction. I’m not sure what image this would produce. Ideas, Dr S?

  21. Markus says:

    Very nice pictures.
    Could it be a kind of Fata Morgana type of reflection, i.e. just due to air density differences?

  22. Kelvin Vaughan says:

    Double glazing?

  23. Jonathan says:

    I have seen this effect, and it was indeed caused by a reflection off of water behind me. Unfortunately, I was to dumbstruck by the sight to go get my camera, which was in my car a few steps away.

    What I saw was a little different, though. Instead of two sets of two, as seen in these pictures, the secondare set (from the reflection) was only a single rainbow. But the primary set was so intense that outer rainbow was continuous from horizon to horizon, and the inner rainbow was double width, going red-orange-yellow-green-blue-violet-red-orange-yellow-green-blue-violet from outside to inside in a continuum.

    The typical double rainbow is a result of a secondary reflection in the raindrop. But I haven’t heard an explanation for a double-wide primary rainbow.

  24. Kevin Hearle says:

    Could it be 2 different sized raindrops in the same area of refraction this might give different angles of refraction thus the appearance of the doubled effect. Further if the number of droplets are not equal in the area then the strength of effect would be unequal.???

    It might be that the different sized droplets are actually separated but close one behind the other rather than together this actually might be more plausible as they might be caused by different but close atmospheric conditions.???

  25. Gordon Robertson says:

    http://www.cbc.ca/news/trending/quadruple-rainbow-puts-double-rainbow-to-shame-but-what-does-it-mean-1.3044092

    “Raymond Lee, a research professor at the U.S. Naval Academy, who spoke to Fast Company, said what we’re really looking here are “sunlight-reflection” rainbows.

    “These rainbows can form when sunlight is reflected from a water surface behind or in front of the viewer, with the result that the sun’s reflected virtual image forms a second light source which appears as far below the horizon as the sun’s real image is above it,” Lee wrote in an email. “A map of the Glen Cove, NY LIRR station shows that Curtis had a great location with Hempstead Bay to the [northwest], nearly opposite the morning sun.””

  26. Thanks, Dr. Spencer.
    This rainbow photographs are complicated to analyze,
    and the are no originals, most “simple” electronic cameras nowadays process the pictures even before storing them in the camera’s memory.

    • Gordon Robertson says:

      “…most “simple” electronic cameras nowadays process the pictures even before storing them in the camera’s memory”.

      Mine is fairly simple but it produces an image of such detail that it wont fit on the average computer screen without zooming down in size.

      As far as processing is concerned, the image needs to be processed into a certain format. However, that should not affect the detail that much if compression is not used.

      Having said that, it’s amazing how much a film-based photo can be enlarged with a microscope for detail. Are you saying it’s not the same with a digitized photo?

  27. michael hart says:

    Deadly super rainbow Percival at The Onion 🙂

    https://www.youtube.com/watch?v=eGMc91yJSgc

  28. KevinK says:

    Dr. Spencer, just in case you are interested here is that link to the Zemax (trademark) software that simulates a rainbow based on basic optical “laws”, Snell’s and Fresnel’s laws mostly.

    https://www.zemax.com/support/knowledgebase/how-to-simulate-a-rainbow

    These are the state of the art modelling tools those of us that work in “applied radiation physics” use day in and day out. Of course the challenge is to match the model predictions to the actual results. We are getting better at that everyday.

    Cheers, KevinK.

  29. nigel says:

    I chanced on the following soon after reading the above about the quadruple bow:

    “There was observed over the Medway Estuary on August 18th (7.15 B.S.T) [1917] an extremely brilliant rainbow. In addition to secondary bows concentric with the primary (all less than a semi-circle) there was seen a bow of considerable brightness having an arc greater than a semi-circle. This “anomalous bow” appeared to be of the same radius as the primary bow, had its colours in the same order (red outer-most) and cut the horizon at the same point. It was, in fact, the remainder of the circle of which the primary arc formed a part.

    The bow in question presumably originated from the image of the sun reflected in the still water of the foreground and thus the right-hand end of the primary bow, which stretched overland, was unaccompanied by the eccentric arc. The phenomenon should not be an uncommon one, yet I do not remember to have observed it previously.

    W. Neilson Jones in Nature September 6th 1917, Page 6.

  30. Jim Bowen says:

    Check out http://www.atoptics.co.uk/rainbows/reflect.htm for an explanation and examples of this. (A reflection from water is given as the explanation.) This web site, http://www.atoptics.co.uk/, is a good resource for exploring most of the atmospheric optics phenomena you may see. It has well-informed explanations.

  31. MikeT says:

    So sad how stupid half the people in this country are. The worst thing is that they think they are capable of critical and analytical thinking, but as these conversations show, the American education system has seriously failed these people over the last 30 years.

  32. tomwys says:

    Gordon Robertson nailed it!!!

    When a rainbow forms, the altitude of the Sun governs the breadth and height of the rainbow (& its secondary). A low, almost grazing, angle that occurs near sunset produces the highest rainbow. If the ground wouldn’t “get in the way,” the bow would be perfectly circular at ALL Sun-Horizon angles, provided sufficient raindrops remained available. The subtlety here is that the above horizon Sun coupled with a low Sun-Horizon angle allowed the “direct” bow to arc fairly high, and be ALMOST semi-circular, while the reflected sunlight coming off a relatively still lake (pond, bay, ocean) has a virtual position below the horizon and thus produces a slightly GREATER THAN semi-circular rainbow. Standard primary/secondary bow effects apply to both rainbows – color reversal and equidistant circular parallelism between primary and secondary bows. This way it is easy to “match” the “above horizon” primary and secondary bows with the virtual “below horizon” paired reflection generated bows.

    The “Glory” that is projected upon thick (usually cumulus) clouds, seen from an airplane with the Sun at any angle, surrounds the plane’s shadow projected upon the clouds. Size of Glory is determined by plane/cloud distance, and secondaries tend to be hard to see because of intrinsic cloud brightness.

    Earth

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