# Circular effect of light through trees - Is there a name for this? **URL:** \ **Category:** Factual Questions\ **Created:** [November 26, 2008, 6:41pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586 "2008-11-26T18:41:25Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Mixolydian](https://avatars.discourse-cdn.com/v4/letter/m/da6949/32.png) [@Mixolydian](https://boards.straightdope.com/u/Mixolydian)\ **Post date:** [November 26, 2008, 6:41pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/1 "2008-11-26T18:41:25Z")
Ever looked at the moon or a streetlight at night through tree branches (especially after it rains) and notice how the reflecting branches seem to “curve” around the light source? I’ve also seen this looking at the reflection of a light on a shiny but scratched surface like a finished schooldesk. So, is there a name for this effect? ---
**Author:** ![BarnOwl](https://avatars.discourse-cdn.com/v4/letter/b/e95f7d/32.png) [@BarnOwl](https://boards.straightdope.com/u/BarnOwl)\ **Post date:** [November 26, 2008, 6:50pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/2 "2008-11-26T18:50:38Z")
No clue about the name of the effect, but I’ll try to remember to check it out tonight, Mixolydian. I’ll have to rely on the moon as the light source. We haven’t many street lights in my town - maybe 5 or so. And no rain in sight. Sounds interesting, though. Is your name related to a form of musical scales? ---
**Author:** ![BarnOwl](https://avatars.discourse-cdn.com/v4/letter/b/e95f7d/32.png) [@BarnOwl](https://boards.straightdope.com/u/BarnOwl)\ **Post date:** [November 26, 2008, 6:56pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/3 "2008-11-26T18:56:46Z")
It is! > **[Mixolydian mode](https://en.wikipedia.org/wiki/Mixolydian_mode)** > > Mixolydian mode may refer to one of three things: the name applied to one of the ancient Greek harmoniai or tonoi, based on a particular octave species or scale; one of the medieval church modes; or a modern musical mode or diatonic scale, related to the medieval mode. (The Hypomixolydian mode of medieval music, by contrast, has no modern counterpart.) > The modern diatonic mode is the scale forming the basis of both the rising and falling forms of Harikambhoji in Carnatic music, the classical mu... ---
**Author:** ![Mixolydian](https://avatars.discourse-cdn.com/v4/letter/m/da6949/32.png) [@Mixolydian](https://boards.straightdope.com/u/Mixolydian)\ **Post date:** [November 26, 2008, 7:04pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/4 "2008-11-26T19:04:29Z")
The more branches/twigs, the better. Maybe get out the hose? 🙂 I should mention that I first noticed this as a teen along with a friend while under the (albeit weak) influence of a hallucinogen. It’s still there without “help” if you look for it. To clarify the OP a bit more, I think it’s similar to what Van Gogh was trying to duplicate in “Starry Night”. > [@BarnOwl](#): > > Is your name related to a form of musical scales? Could be, rabbit… 😉 \ I see you already confirmed…the byproduct of an influential music theory teacher and the mode’s connection to the blues, my genre of choice\ ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [November 26, 2008, 8:43pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/5 "2008-11-26T20:43:40Z")
Minnaert (naturally) discusses the effect in his classic [_The Nature of Light and Colour in the Open Air_](http://www.amazon.com/Nature-Light-Colour-Dover-Sciences/dp/0486201961/ref=sr_1_1?ie=UTF8&s=books&qid=1227731926&sr=1-1), but doesn’t mention a specific name for it. I doubt it has a scientific name, though some artist’s manual might have given it a name at some point. Minneart’s book is filled with detailed, yet clear, explanations of all sorts of such everyday effects. Highly recommended. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [November 26, 2008, 8:44pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/6 "2008-11-26T20:44:02Z")
I think this is a large-scale example of chatoyancy. ---
**Author:** ![BarnOwl](https://avatars.discourse-cdn.com/v4/letter/b/e95f7d/32.png) [@BarnOwl](https://boards.straightdope.com/u/BarnOwl)\ **Post date:** [November 26, 2008, 9:05pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/7 "2008-11-26T21:05:15Z")
> [@Napier](#): > > I think this is a large-scale example of chatoyancy. Why? ---
**Author:** ![Henrichek](https://avatars.discourse-cdn.com/v4/letter/h/5daacb/32.png) [@Henrichek](https://boards.straightdope.com/u/Henrichek)\ **Post date:** [November 26, 2008, 9:41pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/8 "2008-11-26T21:41:32Z")
I don’t remember observing this effect. Is it something that can be captured on photos? ---
**Author:** ![Saltire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saltire/32/553_2.png) [@Saltire](https://boards.straightdope.com/u/Saltire)\ **Post date:** [November 26, 2008, 9:42pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/9 "2008-11-26T21:42:48Z")
Isn’t it just simple diffraction? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 26, 2008, 9:47pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/10 "2008-11-26T21:47:44Z")
> [@](#): > > I think this is a large-scale example of chatoyancy. I don’t think so… On looking up [chatoyancy](http://en.wikipedia.org/wiki/Chatoyancy), it looks like it depends on having some sort of parallel grain in the material, while this effect depends on having linear features running in many different random directions. In case anyone is unclear, in the OP’s effect, there are branches or scratches going every which way; it’s just only those which would appear to encircle the light source which get highlighted. ETA: > [@](#): > > Isn’t it just simple diffraction? No, it’s a purely ray-optics effect, independent of wavelength. And there’s no reason it wouldn’t show up in a photo, so long as you didn’t use a flash. ---
**Author:** ![Henrichek](https://avatars.discourse-cdn.com/v4/letter/h/5daacb/32.png) [@Henrichek](https://boards.straightdope.com/u/Henrichek)\ **Post date:** [November 26, 2008, 9:58pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/11 "2008-11-26T21:58:01Z")
In that case, could anybody be so kind and provide a photograph of this effect? I am curious of what you all seem to have observed. ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [November 26, 2008, 10:33pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/12 "2008-11-26T22:33:15Z")
Courtesy of Google Book Search, here’s the (not wildly clear) [photo](http://books.google.co.uk/books?id=1xpeQ_RwEqgC&pg=PA338&lpg=PA338&dq=tree+minnaert&source=web&ots=HNC1WtrMkm&sig=RLqEzr9XiIekf7EZukpHXjlIG9A&hl=en&sa=X&oi=book_result&resnum=7&ct=result#PPA28-IA1,M1) of the effect from the Dover edition of Minnaert. ---
**Author:** ![Mixolydian](https://avatars.discourse-cdn.com/v4/letter/m/da6949/32.png) [@Mixolydian](https://boards.straightdope.com/u/Mixolydian)\ **Post date:** [November 26, 2008, 11:06pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/13 "2008-11-26T23:06:06Z")
Bonzer, I think I’m going to have to check that book out. 😉 Thank you, all - this one has bugged me for ages, and it ain’t the kind of thing you bring up in any average conversation. The Dope does it again! I also wondered what, if any relationship there was to the phenomenon and the dual particle/wave nature of light, but hey, this is more than I bargained for as it is. Thanks again. ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [November 26, 2008, 11:10pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/14 "2008-11-26T23:10:57Z")
I’m thinking the word is [Anisotropic](http://en.wikipedia.org/wiki/Anisotropy). I know the effect you’re talking about, and it’s basically an anisotropic effect of random etchings at all angles in a surface, rather than a radial etching like that on a brushed aluminum surface. ETA: could be Isotropic. Looking into it… ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [November 26, 2008, 11:43pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/15 "2008-11-26T23:43:01Z")
Well, my best guess for now, is _random anisotropic specularity._ ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [November 28, 2008, 3:47am UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/16 "2008-11-28T03:47:52Z")
\>I don’t think so… On looking up chatoyancy, it looks like it depends on having some sort of parallel grain in the material, while this effect depends on having linear features running in many different random directions. Chatoyancy depends on parallel grains scattering light in the plane perpendicular to the grain and containing the source. The effect described in the OP is scattering by the sufficiently nearly parallel fraction of all the randomly oriented structures in this same configuration. That is, all the branches are random, but the reflecting subset in a particular region are all nearly parallel and tun perpendicular to the plane containing the reflecting spots, the sun, and the observer. I say in a particular region because as you travel around the line of sight to the sun, their angle changes. So, I think the effect the OP notices is that, of all the branches, those that are at the right angle are emphasized by reflecting, which is chatoyancy at work; and, this is on a large scale a circular grain effect because you are rotating the plane in which the branches are made reflecting. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [November 28, 2008, 12:42pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/17 "2008-11-28T12:42:45Z")
An easy place to spot it is on car paintwork when the sun reflects off it. The tiny random scratches in the paintwork from washing it show up in a circle around the image of the sun. [Here’s](http://www.attention-2detail.co.uk/userimages/d(1).jpg) an example (using a lamp rather than the sun). Edit: and [here](http://m.b5z.net/i/u/6116466/i/400_bmwbefore_1_.jpg) is another which shows the effect more clearly. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [November 28, 2008, 2:34pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/18 "2008-11-28T14:34:41Z")
With regard to trees, isn’t this an example of fractals? So that when the tree is in leaf it captures the maximum amount of sun? ---
**Author:** ![Ponderoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ponderoid/32/19221_2.png) [@Ponderoid](https://boards.straightdope.com/u/Ponderoid)\ **Post date:** [November 28, 2008, 5:00pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/19 "2008-11-28T17:00:18Z")
Is this effect related at all to how you can look down at the [ground under a tree during an eclipse](http://apod.nasa.gov/apod/ap001225.html) and see multiple crescents on the ground? \*\*\* Ponder ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [November 28, 2008, 6:56pm UTC](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586/20 "2008-11-28T18:56:33Z")
> [@Ponderoid](#): > > Is this effect related at all to how you can look down at the [ground under a tree during an eclipse](http://apod.nasa.gov/apod/ap001225.html) and see multiple crescents on the ground? > > \*\*\* Ponder No, what you’re talking about is related to the [Bokeh Effect,](http://en.wikipedia.org/wiki/Bokeh) I believe. Entirely different than what the OP is asking about. See Colophon’s pics. [Next page](https://boards.straightdope.com/t/circular-effect-of-light-through-trees-is-there-a-name-for-this/474586.md?page=2)