Wikipedia:Featured picture candidates/Tyndall effect at CN Tower

Tyndall effect at CN Tower
Voting period ends on 14 Feb 2011 at 15:56:08 (UTC)
 * Reason:educational image, nice view as well
 * Articles in which this image appears:Tyndall effect
 * FP category for this image:
 * Creator:Wladyslaw


 * Support as nominator --– Wladyslaw (talk) 15:56, 5 February 2011 (UTC)
 * Question I don't get it... would any picture of the sky do? Aaadddaaammm (talk) 16:29, 5 February 2011 (UTC)
 * the Tyndall effect is not in every picture of the sky visible. --93.194.112.24 (talk) 10:12, 6 February 2011 (UTC)
 * I read that already, and I read it again, and I still don't get it. What are we looking at in this photo? Aaadddaaammm (talk) 10:22, 6 February 2011 (UTC)


 * Oppose. I don't think the sky looks that nice near the sun (concentric bands visible). Also, as I said at its Commons FPC, I don't believe that what we're seeing here is a good example of the Tyndall effect. I don't see any difference in colour, just brightness; like a fog shadow without the fog. --Avenue (talk) 03:46, 7 February 2011 (UTC)
 * I'm with you. I think this is the shadow of the building in the car-exhaust haze. Chick Bowen 15:20, 8 February 2011 (UTC)
 * And that is exactly what the Tyndall effect (or rather the absence thereof in the shadow) is. --Dschwen 20:19, 10 February 2011 (UTC)
 * No - see my response to your post below. --Avenue (talk) 05:17, 11 February 2011 (UTC)
 * Actually Yes, car-exhaust is given as an example in the article. You make a different argument, namely that it is not small particulate exhaust, but larger particulates that scatter. --Dschwen 19:03, 11 February 2011 (UTC)
 * Oppose: I read the article, looked at the picture, read the article again and looked at the picture again, but I still couldn't see any evidence that of the effect. The sky is normally blue due to Rayleigh scattering, a different phenomenon, and it seems a bit unlikely to see more blue on top of something that is already blue. The glass of blue flour is a much better example. Interesting picture but I don't see the EV for the article it's in.--RDBury (talk) 17:55, 9 February 2011 (UTC)
 * Tyndall effect is based on Mie scattering. Rayleigh scattering is a different beast and is not of relevance here (other than causing the backdrop for the effect to be blue). --Dschwen 20:21, 10 February 2011 (UTC)
 * Oppose. Seems like OR to assert that this is an example of the Tyndall effect... furthermore, this image should perhaps even be removed from that article. --Dante Alighieri | Talk 22:51, 9 February 2011 (UTC)


 * Two years ago I asked german physicans at de.wikipedia about this picture. They told me and constituted that this effect on the picture is the tyndall effect. But maybe be physics in USA/GB is different to this in germany ;-) --– Wladyslaw (talk) 13:10, 10 February 2011 (UTC)
 * Sorry but I see no answer that this is the tyndall effect. Like "Das: Tyndall-Effekt müsste es doch sein. Es ist einfach der Dunst + Staub in der Atmosphäre.", written by Alchemist-hp, translated: "This: It must be the Tyndall-effect. It's just dust and mist in the atmosphere."-- ♫Greatorangepumpkin♫ T 16:01, 10 February 2011 (UTC)


 * Comment. I'm pretty certain that the reason for the light/shadow phenomenon in the picture is Mie scattering on dust/smog particles in the Toronto air (the article itself mentions blue motorcycle exhaust). However the image has a slight shortcoming, namely it does give no hint of the frequency dependence of this scattering process, which might be the main source for the confusion in this nomination. --Dschwen 20:26, 10 February 2011 (UTC)


 * Mie scattering I could believe. According to our Mie theory article, Mie scattering is not frequency dependent roughly independent of wavelength, which would agree with what we see in this image. It is also caused by a much wider range of particle sizes than would produce the Tyndall effect (according to our Tyndall effect article, which says that effect occurs with suspended particles of between roughly 40 and 900 nanometers). Particulate pollution in Toronto seems to be dominated by much larger particles, i.e. between 2500 and 10000 nanometers. (See Table I in M.E. Campbell, Q. Li, S.E. Gingrich, R.G. Macfarlane, and S. Cheng (2005). Should people be physically active outdoors on smog alert days?, Canadian Journal of Public Health, 96(1), 24-28.) Perhaps this image should be put in the Mie theory article instead, in the section on applications in atmospheric science where it talks about how Mie scattering causes haze and occurs mostly in the lower portions of the atmosphere where larger particles are more abundant. --Avenue (talk) 05:17, 11 February 2011 (UTC)
 * Uhm, in the range of particles sizes around and below the wavelength of the scattered light Mie theory predicts a fourth power dependence of intensity on wavelength. That is the opposite of "roughly independent". For much larger particles you do not need Mie theory, that is just scattering by reflection. --Dschwen 18:56, 11 February 2011 (UTC)
 * Just to clarify: Tyndall effect occurs in a subrange of particles sizes whose scattering is described by Mie theory. So, I have to agree, that the picture shows scattering (which can be described by Mie theory), but it does not show an obvious frequency dependence. Ultimately that makes it a weak illustration for the Tyndall effect. ---Dschwen 19:01, 11 February 2011 (UTC)

--Makeemlighter (talk) 19:03, 14 February 2011 (UTC)