Seeing double: Researchers find rainbow connection
A twinned rainbow, pictured in foreground, happens rarely, when the primary bow splits in two.
December 9th, 2011
11:36 AM ET

Seeing double: Researchers find rainbow connection

YouTube has taught us that a double rainbow may be worthy of an ecstatic rant. But there's a natural multicolored phenomenon even more spectacular: a twinned rainbow.

A twinned rainbow happens when the primary bow splits in two.  Scientists have found out more about how this rare event happens by using sophisticated computer science techniques.

Iman Sadeghi, a software engineer in Google's graphics division, did research on the physics of rainbows while pursuing his doctorate at the University of California, San Diego. He and his adviser, Henrik Wann Jensen, who worked on the James Cameron film “Avatar," collaborated with scientists from Spain, England and Switzerland. The team plans to publish the results in the journal ACM Transactions on Graphics.

Sadeghi and colleagues set out to reproduce different rainbows. They created computer simulations to recreate the geometry of a real raindrop and capture the behavior of light as it leaves water drops.

In a primary rainbow, light gets reflected from water droplets and then comes out. In a secondary rainbow, light gets reflected twice in the droplet before emerging.

But what about twinned rainbows? By looking at simulations, Sadeghi and colleagues realized that spherical water drops cannot possibly produce that effect.

Instead, you'd need a rain shower with both small spherical water drops and larger, flatter droplets that they call "burgeroids" because they look like hamburgers. The burgeroids shift light in one direction, while the small droplets produce a separate bow.

It takes a uniform distribution of large drops of water of the same size to produce a twinned rainbow, Sadeghi said. Since that's usually not the case, twin rainbows are rare.

This research is "the first scientific, accurate simulation of twinned rainbow in history," Sadeghi said. "We ended up pushing the edge of rainbow science."

These findings might be useful for a film or video game maker concerned with scientific accuracy in the portrayal of rainbows, although typically those media don't pay attention to such details, Sadeghi said.

Sadeghi's method is a lot slower than just copying an existing photo of a rainbow - each water drop you want to simulate takes six hours, he said.

"The application is very narrow for specific people who care about the appearance of rainbows," he said. "But if a movie wants a twin rainbow, they should definitely come to us."

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Filed under: On Earth
soundoff (100 Responses)
  1. shutterfly coupon

    hello awesome article shutterfly coupon

    June 20, 2013 at 5:53 pm |
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    "I learn at once!" Zhang Jin ought to sentence position Yun claimed: "Oh, the evening I'm going for you, you need to start off coaching."
    athletic discontinued mbt shoes but Lin Fei in the game

    October 21, 2012 at 5:50 pm |
  3. Jenn

    Never thought I'd see people this angry about rainbows. Thanks Internet! 😀

    December 11, 2011 at 3:01 pm |
    • Lifeless Troll

      Rainbows and puppies tick me off.

      December 11, 2011 at 3:16 pm |
    • Gerrie Warner

      I actually have a real photo of a triple rainbow. Taken i Östhammar, Sweden in 1974

      January 2, 2012 at 1:18 pm |
  4. paula

    at least all animals go to heaven.

    December 11, 2011 at 2:08 pm |
  5. matinee

    How I love this is heartening to read comments on people with religious belief and that of science belief.God created MAN, endowned man with wisdom,understanding,knowledge,freewill to explore the universe. Keep it coming please..

    December 11, 2011 at 12:21 pm |
    • fimeilleur

      And then he condemned his lineage for all eternity to be damned in hell for "sin" of wanting to know right from wrong.... Oh yeah baby, your god is good... (sarcasm)

      December 12, 2011 at 1:06 am |
  6. ttown

    double rainbow all the way!

    December 11, 2011 at 12:00 pm |
  7. SyrianSynic


    December 11, 2011 at 4:04 am |
    • Rainbow Shmainbow

      God don't got no mother you son of a donkey.

      December 11, 2011 at 3:13 pm |
  8. Rahul

    To the Christian poster below me: get prepared to be ridiculed.

    December 11, 2011 at 2:34 am |
    • Lol to you

      Double double rainbows all across the sky, yeah yeah oh my God... what does it mean.!

      December 11, 2011 at 2:42 pm |
  9. Michael

    How do they explain triple rainbows?

    December 11, 2011 at 1:29 am |
    • Don Eduardo

      Too much tequilla.

      December 11, 2011 at 3:05 pm |
  10. Houstonian

    Ya'll get off Amy's chukus. I can't see the pretty picture either... Because the MOBILE version of this site usually usually DOES NOT have the pictures that the desktop version has. Sheesh. Give the girl a break.

    December 10, 2011 at 11:47 pm |
  11. shiga

    From watching slow motion videos of rain falling in the Amazon on the Discovery Channel, you can clearly see that rain droplets shift, in fact I do not know why this article implies that scientists thought all rain looked the same.
    I really doubt the authenticity of half the things stated within this article.

    December 10, 2011 at 9:31 pm |
    • tetrahedron

      doesn't it have something to do with the size of the tetrahedron (water molecule) and light bouncing off of a certain sized tetrahedron? so a fine mist would do it. so to get doubles we have to figure out how to get the garden hose to have a mist with burgeroids. ok. thanks.

      December 11, 2011 at 12:55 am |
  12. southern_gent_from_mississippi

    By the way, Ive seen 2 double rainbows, here in Mississippi, within the last 6-8 months so I think theyre becoming more common these days. Probably because of more pollution in the air.

    December 10, 2011 at 1:49 pm |
    • shiga

      Or because they are very common despite what these researchers say,I see them all the time in Oregon one of the least polluted states.

      December 10, 2011 at 9:28 pm |
      • Alinnc

        Saw a couple in a few months in NC about two years ago, none since, but have not seen many rainbows since then either. Does not seem to be an exceptionally rare occurance.

        December 10, 2011 at 11:03 pm |
    • TUSK80

      TWINNED RAINBOWS! That is what the article is about!
      Not double rainbows!
      Read and comprehend!
      Totally amazing at the people on these message boards that don't comprehend what they have just supposedly read!

      December 11, 2011 at 11:17 am |
  13. southern_gent_from_mississippi

    Bible thumper, do you have nothing better to do than cut and paste stories of the baddest mass murderer/terrorist of all times? Sorry but I dont see how someone who destroyed entire towns and eventually murdered the entire world, except for a few on a boat, has relevance to this story?

    December 10, 2011 at 1:47 pm |
  14. Leigh

    Really!!! We are spending money on reseaching this instead of a cure for Cancer, Aids, or ect..really don't know what to say!! Smh.

    December 10, 2011 at 12:28 pm |
    • Mitchell

      we are spending MILLIONS on all of those......

      this just took a computer and a bright mind to figure out

      December 10, 2011 at 2:45 pm |
    • MandoZink

      Researching how light refracts in a water droplet's cavity is definitely MUCH cheaper, and simpler, than any AIDs or cancer research. It is really pretty basic science. Did you know that this particular science concept has led to production of something called "quantum dots", which is currently being developed into a new type of highly efficient lighting? This development will help reduce pollution from power generation, which should improve our health as a result. I approve of basic research like this. It leads to other improvements of our condition, whether you know this or not.

      By the way, I also have a framed photograph of 2 double rainbows (thats 4 of them) which I took on a trip in Colorado at the tail end of a magnificent dark storm just after it crossed the Rockies. The clouds were near black, the sun had just began shining again from the west above the mountains, and the wind had kicked up a bright tan dust storm that the rainbows dipped into. Stunning!

      December 10, 2011 at 2:54 pm |
      • beauty be seen

        Post the picture of your rainbow on you tube would love to see it...also ahve seen 1/2 dozen double rainbows in MO but not that vivid. science is good! but the universe is better.

        December 11, 2011 at 8:38 am |
  15. Stevo304

    Amen for rainbows.. GOD is good..

    December 10, 2011 at 10:08 am |
    • fimeilleur

      Yes, Ra is a good and glorious god, but then again, so is Zeus, and Thor... not a fan of Baal, but Vishnu is probably my favourite.

      December 11, 2011 at 3:35 am |
      • Julzrael

        Mmmmmm I love my Gods and Goddesses: Primaries: Isis, Bast, Athena, Venus, Mercury, Mars, Saturn, Ganesha. Though I do love Asklepios, Thoth and Jesus added in the mix for healings and Hestia, Vesta, Brigid, and Bride for housecleaning. What do you think of a new God Technos or Technia for all things tech? 🙂 May the Gods Smile upon us ALL! Living Myths. Awesome!!!!!!!!!

        December 11, 2011 at 1:25 pm |
      • fimeilleur


        December 12, 2011 at 12:59 am |
  16. pauliewallie

    i have a picture of a primary and secondary rainbow or twin rainbow on my phone. I took it back in august i think. Wish i could put it on here.

    December 10, 2011 at 8:21 am |
  17. lee

    Rainbows are beautiful because they are a sign from God.

    December 10, 2011 at 8:07 am |
    • austin

      No its not. God has nothing to do with rainbows. Its water particles reflecting the prism of light. Simple. Did u go to school?

      December 10, 2011 at 2:09 pm |
      • ng2091

        um a rainbow is a sign to us from God that is a reminder of his promise not to flood the earth like he did in Noah's Arc. Have you read your Bible? reguardless of how they are made it is still God's creation and is a sign!

        December 11, 2011 at 3:05 am |
      • Amy

        People still die in floods today every year *cough Tsunami*, and they see rainbows afterwards while holding their dead babies.. miracle? or is God just having good laugh.

        December 11, 2011 at 10:45 am |
  18. OrangeW3dge

    Go to Hawaii, it's quite common there

    December 10, 2011 at 5:26 am |
  19. BeerBrewerDan

    "We ended up pushing the edge of rainbow science."

    Dude...I totally did that at a Dead show back in '87.

    December 9, 2011 at 9:31 pm |
  20. Mike

    I've caught one of these before! Couldn't tke my eyes off of it for 15 minutes... Definitely the most beautiful rainbow I've ever seen

    December 9, 2011 at 9:15 pm |
  21. zoey zatsune


    December 9, 2011 at 9:09 pm |
  22. prancypants

    It's starting to look like a triple rainbow.

    December 9, 2011 at 8:36 pm |
  23. prancypants

    WHOA, that's a full rainbow.

    December 9, 2011 at 8:36 pm |
  24. DB

    How about a rainbow at night ?
    Saw one this evening with a very bright moon and St Thomas VI in the background.
    Or would you call this a moon bow ???

    December 9, 2011 at 8:04 pm |
  25. AmosGraber

    You city folk should get out more often; this article is wrong in saying it is rare I see this all the time out here on the plains of Colorado, not rare at all

    December 9, 2011 at 7:43 pm |
  26. Mr. Get it Straight

    Saw a sngle rainbow on Oahu and a double in godd%$#$ New Jersey. The mere fact that it was in NJ robbed it of half of its beauty ...

    December 9, 2011 at 7:14 pm |
    • hawaiiduude

      but hawaiian rainbows have a higher THC content...

      December 9, 2011 at 7:21 pm |
    • letsgomets2012

      Haha, very funny.

      Jersey RULES.

      December 9, 2011 at 8:13 pm |
  27. mildred

    there was a unicorn near by farting rainbows. that's my explanation for anything magical

    December 9, 2011 at 7:06 pm |
    • Did Ya

      Bet you sure enjoyed Sniffing it didn't ya, Millie! 🙂

      December 9, 2011 at 7:28 pm |
      • Guest

        Unicorn farts smell like cupcakes

        You should see how they taste!

        December 10, 2011 at 11:29 am |
  28. bradley

    Well this must be big news in Rainbow bright world :)) I seen one double and one tripple myself. Seen the double on Lake Mendocino and another tripple in the foothills one bow to every hill too. Wish had camera.

    December 9, 2011 at 6:36 pm |
  29. Cynthia

    Twice I've witness perfect triple rainbows. Once in Crested Butte, Colorado and once on Maui. Both places are magical and to witness this was awesome against the scenery.

    December 9, 2011 at 6:17 pm |
  30. Buggy

    We had massive flooding in September here in the Northeast. The day most people who had evacuated were allowed to go home, there was an amazing double rainbow in the sky. I had never seen one before that day.

    December 9, 2011 at 6:07 pm |
    • illmatar

      Every rainbow has a twin, but the second is so faint it is usually overlooked unless the first is very strong.

      December 9, 2011 at 6:49 pm |
      • Pay Attention

        "illmater" – if you carefully read the article, you'd know that not every rainbow has a "twin". There are DOUBLE rainbows, but TWINNING rainbows are rare – READ THE ARTICLE to understand the difference...jeez.

        December 9, 2011 at 7:28 pm |
  31. Truetuft

    And GOD said to me......, just the other day at brunch, "...and the rainbow must appear in the cloud...They are kinda pretty! Don't you think?" – That booming voice always scares the waitress.

    December 9, 2011 at 5:51 pm |
  32. Cusao

    This can happen in nature. I have photos to prove it. It is caused by a reflection of the sun on water. At sunrise with very flat water behind you, you will see exactly what was shown in the above photo. Two regular rainbows and a third with its origin in the base of one of the regular rainbows. If things were very bright, there would be a fourth rainbow.

    December 9, 2011 at 5:50 pm |
    • Yossarian

      That process creates additional rainbows but they would be situated in a different part of the sky.

      December 9, 2011 at 5:59 pm |
    • huddy

      I saw a quadruple several years ago. There was a small rain shower right in front of the setting sun. The whole sky went golden and for about 10 minutes, there was a quadruple rainbow, two pairs of doubles. 3 of the 4 were full semi-circular rainbows.

      December 10, 2011 at 12:10 am |
  33. alfa0mega939

    I took a picture of one of these twinned bows within the last two months. I had never seen one before. I'm really glad someone figured out how they're made.

    December 9, 2011 at 5:45 pm |
  34. Pete

    so intense

    December 9, 2011 at 5:35 pm |
  35. TY

    It strikes me how almost all of these scientific articles seem to be followed closely by people with strong religious/myth-based viewpoints... Finding the need to profess on articles of such agnostic logic makes me think you doubt yourselves… Just saying…

    December 9, 2011 at 5:31 pm |
  36. RIcky Bobby

    If only those burgeroids were real burgers (i.e. cloudy with a chance of meatballs)! Now THAT would be something! Come on scientists, let's get to work

    December 9, 2011 at 5:27 pm |
    • Corey

      Now Im hungry for rainbows!!

      December 9, 2011 at 5:46 pm |
    • park

      littomika on August 30, 2011 I like that I am a getraful person. I love being able to show my appreciation to others and count all of my blessings. I dont like taking things for granted, because life is so special and the people you love should feel they are loved.

      March 4, 2012 at 3:10 pm |
  37. Mary

    What does this MEAN?

    December 9, 2011 at 5:21 pm |
    • crazycatman

      It means that nature produces beautiful things. Why does it have to MEAN anything else?

      December 9, 2011 at 5:57 pm |
      • Muggle92

        Apparently you've never seen the video.

        December 9, 2011 at 6:18 pm |
    • Clark Nova

      It MEANS that physics can explain everything, eventually.

      December 9, 2011 at 7:43 pm |
  38. michael

    for amazing amount of information on atmospheric phenomena...

    December 9, 2011 at 5:11 pm |
  39. david

    There was no bow before Noah because it had never rained before then. Nothing to do with physics.

    December 9, 2011 at 5:05 pm |
    • dave


      December 9, 2011 at 5:29 pm |
    • Daws

      Lol that must have sucked for plants. Were there also no rivers and snow? 😛

      December 9, 2011 at 7:48 pm |
  40. amy

    Would of been nice if they had a picture of said rainbow....if they did, I didn't see it

    December 9, 2011 at 4:39 pm |
    • elandau

      Hi, the picture is at the top of the post. Thanks for reading!
      Elizabeth Landau, CNN

      December 9, 2011 at 4:40 pm |
      • Rainbow girl

        The whole picture shows a double rainbow, the one that is considered a twinning rainbow (split rainbow) is the one in the bottom right hand corner. If you look at it you can see about 1/3 of the way up it split and becomes two rainbows., the colors repeat.

        December 9, 2011 at 4:55 pm |
    • Seriously?

      Amy, Seriously? You're saying you don't see a "twinned" rainbow, even though the caption reads "twinned rainbow, pictured in foreground..."? My god, what is happening to education in this country????????????????????? Why are you on this article site, and why bother entering a comment, if you haven't read the article (which thoroughly explains it) and don't even look at the picture AND the caption? I am terrified for the human race...

      December 9, 2011 at 5:42 pm |
      • tiredofhyperbole

        Relax, Seriously. There have always been, and will always be, people dumber than hammers. Who else would we elect?

        December 9, 2011 at 5:57 pm |
      • alc

        @tiredofhyperbole – I'm sure that there are a number of hammers that are offended by your comment (and the fact that no one has elected them yet)

        December 9, 2011 at 6:11 pm |
      • Chris

        Amy for President!

        December 9, 2011 at 6:14 pm |
  41. cklutch

    Double complete rainbow

    December 9, 2011 at 4:35 pm |
  42. Miguel

    Very interesting! Just understanding it is cool, but i wonder how we will apply more advanced knowledge of light refraction.

    Thank you for copy and pasting a bible story that i learned when i was three, in KJV to boot. How about some real discussion?

    December 9, 2011 at 4:25 pm |
  43. Dino

    It is time to replicate these tin rainbows artificilly. Put them in city centers or touristic places!

    Scienc can do it!

    December 9, 2011 at 4:21 pm |
    • Miguel

      in an economy with surplus deficit, things like this might happen again.

      December 9, 2011 at 4:26 pm |
  44. A Promise for Mankind

    Genesis 9:8-17

    8 And God went on to say to Noah and to his sons with him:

    9 “And as for me, here I am establishing my covenant with YOU men and with YOUR offspring after YOU,

    10 and with every living soul that is with YOU, among fowls, among beasts and among all living creatures of the earth with YOU, from all those going out of the ark to every living creature of the earth.

    11 Yes, I do establish my covenant with YOU: No more will all flesh be cut off by waters of a deluge, and no more will there occur a deluge to bring the earth to ruin.”

    12 And God added: “This is the sign of the covenant that I am giving between me and YOU and every living soul that is with YOU, for the generations to time indefinite.

    13 My rainbow I do give in the cloud, and it must serve as a sign of the covenant between me and the earth.

    14 And it shall occur that when I bring a cloud over the earth, then the rainbow will certainly appear in the cloud.

    15 And I shall certainly remember my covenant which is between me and YOU and every living soul among all flesh; and no more will the waters become a deluge to bring all flesh to ruin.

    16 And the rainbow must occur in the cloud, and I shall certainly see it to remember the covenant to time indefinite between God and every living soul among all flesh that is upon the earth.”

    17 And God repeated to Noah: “This is the sign of the covenant that I do establish between me and all flesh that is upon the earth.”

    December 9, 2011 at 4:11 pm |
    • Casey


      December 9, 2011 at 4:23 pm |
    • gupsphoo

      So there were no rainbows before the flood and God changed the laws of physics for Noah? LOL!

      December 9, 2011 at 4:36 pm |
    • SixDegrees

      The Bible never mentions twinned or double rainbows, so like evolution and dinosaurs they are either 1) fake, or 2) the work of Satan.

      [end sarcasm]

      December 9, 2011 at 5:04 pm |
      • Jealous...

        You are indeed a perfect logician.

        December 9, 2011 at 5:42 pm |
      • T3chsupport

        Fool. Obviously rainbows are evolving.

        December 9, 2011 at 5:52 pm |
    • dave


      December 9, 2011 at 5:32 pm |
    • Jason

      Funny, had it been a bird flying over that left some dropping on Noah's head, we'd now have the "sign" that bird crap is some holy sign from god. Oh well, one day man will grown up and stop believing in fairy tales.

      December 9, 2011 at 6:05 pm |
    • SKYNET

      It works so much better when you have colorful characters outlined in black with dialogue balloons for the text.

      December 9, 2011 at 6:05 pm |
    • Clark Nova


      December 9, 2011 at 7:46 pm |
    • Reason

      The is no such thing as santa, easter bunny, ghosts/souls, and magical sky fairies. Welcome to the 21st century.

      December 10, 2011 at 12:32 pm |


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