APOD: Rainbow at Sunset (2010 Aug 07)

Comments and questions about the APOD on the main view screen.
myxlpyx

Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by myxlpyx » Sun Aug 08, 2010 12:58 am

I'm sure I have once seen a rainbow forming a circle around the sun, rather than in the opposite direction to the sun as is common. The sun was high in the sky, there were clouds in the sky and I think it was raining very slightly. Has anyone else ever seen this before, or can I not trust my memory anymore?

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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by Chris Peterson » Sun Aug 08, 2010 1:05 am

myxlpyx wrote:I'm sure I have once seen a rainbow forming a circle around the sun, rather than in the opposite direction to the sun as is common. The sun was high in the sky, there were clouds in the sky and I think it was raining very slightly. Has anyone else ever seen this before, or can I not trust my memory anymore?
It was certainly not a rainbow. There are a number of halo effects that can be seen around the Sun, and some have associated (rainbow-like) color, although usually less saturated than a rainbow. The optical mechanism for these halo effects is different from that of a true rainbow.
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by Beyond » Sun Aug 08, 2010 1:23 am

Neufer, the Sno-Ball effect that effects me is lack of consumption of them. Around here they are almost as scarce as hen's teeth.
The only thing that Sno-Balls and rainbows have in common is that dome shape. Even though you can not physically eat a rainbow, there are many people that "eat them up with their eyes." I can not say that i blame them. Rainbows can be quite a big piece of eye candy.
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by alter-ego » Sun Aug 08, 2010 1:41 am

neufer wrote: Photons play a secondary role by creating those diffraction effects seen around 1 O'clock in today's APOD.
What diffraction effects are you referring to? I don't see anything but the supernumeraries and they do not require photons to describe them per atoptics link. As stated, the wave property of light needs to be invoked (in addition to standard ray tracing) but not the particle behavior.
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by neufer » Sun Aug 08, 2010 2:11 am

alter-ego wrote:
neufer wrote: Photons play a secondary role by creating those diffraction effects seen around 1 O'clock in today's APOD.
What diffraction effects are you referring to? I don't see anything but the supernumeraries and they do not require photons to describe them per atoptics link. As stated, the wave property of light needs to be invoked (in addition to standard ray tracing) but not the particle behavior.
OK, I skipped a step:

1) The Snell–Descartes law defines classical rainbow(s) in terms of Newtonian light particles.
2) EM wave theory defines the supernumeraries
3) Photon theory defines the supernumeraries in terms of quantum light particles.

(It's hard thinking "beyond" the fringe.)
http://www.atoptics.co.uk/droplets/fogdrpsz.htm wrote:
<<Fogbows form in the same way as rainbows. A small fraction of the light entering
droplets is internally reflected once and emerges to form a large circle opposite the sun.


But... ...beyond that there are major differences. Rainbows are formed by raindrops which are so large that rays passing through them follow well defined 'geometrical optics' paths. Fogbows are formed by much smaller cloud and fog droplets which diffract light extensively. The emergent light is mostly deviated 135 to 150° from its incident direction to produce the main fogbow of 30 - 45° radius centered on the antisolar point. The deviation corresponds roughly to the geometric optics angle of minimum deviation of ~138° for the 42° radius rainbow.

Fogbows are almost white with faint reds on the outside and blues inside. The colours are so washed out because the bow in each colour is very broad and the colours overlap. Widely spaced supernumerary bows inside the main arc are produced by the constructive and destructive interference of overlapping wave crests along the main light path.
ImageImage
As the droplet diameter (shown above in microns) increases, the bow narrows and the inner supernumerary bows move closer together. Eventually, for raindrops larger than 1 mm diameter, diffraction effects become small and we have a rainbow with bright colours and hardly noticeable supernumeraries. Cloud and fog droplets rarely exceed 100 micron diameter. The bows intermediate in appearance from 100 - 500 micron dia. droplets are occasionally seen in the sprays of waterfalls.>>
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by Beyond » Sun Aug 08, 2010 2:59 am

Neufer wrote -"It's hard thinking "beyond" the fringe." I resemble that remark :!: The "fringe' is that place that is somewhere over the Rainbow that we can not see because there are no photons there.
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by alter-ego » Sun Aug 08, 2010 4:42 am

neufer wrote:
alter-ego wrote:
neufer wrote: Photons play a secondary role by creating those diffraction effects seen around 1 O'clock in today's APOD.
What diffraction effects are you referring to? I don't see anything but the supernumeraries and they do not require photons to describe them per atoptics link. As stated, the wave property of light needs to be invoked (in addition to standard ray tracing) but not the particle behavior.
OK, I skipped a step:

1) The Snell–Descartes law defines classical rainbow(s) in terms of Newtonian light particles.
2) EM wave theory defines the supernumeraries
3) Photon theory defines the supernumeraries in terms of quantum light particles.
Well I have to agree that the photon theory must be consistent with the EM theory. There's no doubt, in principle, we would recreate the rainbow with supernumeraries if we had a single-photon, broadband source matching the sun's spectral content, then by definition, the photon theory would be required.
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by Chris Peterson » Sun Aug 08, 2010 4:55 am

alter-ego wrote:Well I have to agree that the photon theory must be consistent with the EM theory. There's no doubt, in principle, we would recreate the rainbow with supernumeraries if we had a single-photon, broadband source matching the sun's spectral content, then by definition, the photon theory would be required.
I'm not sure what this "photon theory" is you're going on about. It isn't required to explain diffraction. All optical effects can be explained using either wave or particle models. Diffraction is easier to understand using wave equations, but quantum mechanics unifies wave and particle theories, so you can use either.
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by alter-ego » Sun Aug 08, 2010 4:58 am

beyond wrote:Neufer wrote -"It's hard thinking "beyond" the fringe." I resemble that remark :!: The "fringe' is that place that is somewhere over the Rainbow that we can not see because there are no photons there.
Or, the "fringe" is the dark place in between that's only created by the "addition" of photons that have to be there :!: It's a misperception to say there are no photons there.

Just though you might like that viewpoint :wink:
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by alter-ego » Sun Aug 08, 2010 5:06 am

Chris Peterson wrote:
alter-ego wrote:Well I have to agree that the photon theory must be consistent with the EM theory. There's no doubt, in principle, we would recreate the rainbow with supernumeraries if we had a single-photon, broadband source matching the sun's spectral content, then by definition, the photon theory would be required.
I'm not sure what this "photon theory" is you're going on about. It isn't required to explain diffraction. All optical effects can be explained using either wave or particle models. Diffraction is easier to understand using wave equations, but quantum mechanics unifies wave and particle theories, so you can use either.
I read Art's post literally as requiring quantum theory to describe supernumeraries, which if posted as such, is not true. Classical EM does fine with this, whereas some phenomena it fails. Also, I'm just having some fun with Art. If I get a chance to keep him on his toes, I'll take it :)
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by Beyond » Sun Aug 08, 2010 6:07 am

alter-ego wrote:
beyond wrote:Neufer wrote -"It's hard thinking "beyond" the fringe." I resemble that remark :!: The "fringe' is that place that is somewhere over the Rainbow that we can not see because there are no photons there.
Or, the "fringe" is the dark place in between that's only created by the "addition" of photons that have to be there :!: It's a misperception to say there are no photons there.

Just though you might like that viewpoint :wink:
All viewpoints have their part in the overall scheme of things. But the fringe that i spoke of needs no photons. It has it's own light, so it is not a misperception to say that there are no photons there. However, photons are needed here to be able to see Rainbows and Apods and things. :D
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by alter-ego » Sun Aug 08, 2010 6:08 pm

beyond wrote: All viewpoints have their part in the overall scheme of things. But the fringe that i spoke of needs no photons. It has it's own light, so it is not a misperception to say that there are no photons there. However, photons are needed here to be able to see Rainbows and Apods and things. :D
Of course. I was also trying to provoke thoughts beyond the immediate technical discussion, and it was your reply that prompted mine.
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Myxlpyx = Mxyzptlk = Btfsplk?

Post by neufer » Sun Aug 08, 2010 7:32 pm

http://en.wikipedia.org/wiki/Joe_Btfsplk wrote:
<<Joe Btfsplk was a character in the satirical comic strip Li'l Abner by cartoonist Al Capp (1909–1979). He's well-meaning, but is the world's worst jinx, bringing disastrous misfortune to everyone around him. A small, dark rain cloud perpetually hovers over his head to symbolize his bad luck. According to Al Capp, btfsplk is a rude sound. During public lectures, Capp demonstrated this phatic sound by closing his lips, leaving his tongue sticking out, and then blowing out air, which is colloquially called a "raspberry" or Bronx cheer. Joe Btfsplk may have been the inspiration for the name of the impish character Mr. Mxyzptlk from the Superman comic books. Superman's fifth-dimensional nemesis, originally named "Mr. Mxyztplk", debuted in September 1944. Btfsplk had first appeared in June 1942.>>
http://en.wikipedia.org/wiki/Mister_Mxyzptlk wrote:
<<Mr. Mxyzptlk, sometimes called Mxy, is a fictional impish supervillain in DC Comics' Superman comic books. Not being bound by our physical laws, he can do things that seem to be magical. Originally, Mxyzptlk has designs on conquering the planet for himself, but soon settles for tormenting Superman whenever he gets the opportunity. His only weaknesses are that he can not stand being ridiculed and if he says or spells his name backwards, Kltpzyxm (kil-tip-ZEE-zim), he is involuntarily sent back to his home dimension for a minimum of 90 days. Mxyzptlk often looks for ways to counter the latter weakness, but he always proves gullible enough for Superman to trick him time and time again. Saying "Klptzyxm" will not only bring Mxyzptlk back to the fifth dimension, but would bring anyone else saying it to the fifth dimension. To return back to his/her home dimension, one has to say his/her own name backward. However this specific limitation of the character has been eliminated since the Crisis on Infinite Earths reboot, upon which the character only leaves because he willingly agrees to do so after meeting some conditions he sets, such as having Superman succeed in painting Mxy's face blue.>>
ImageImage
Chris Peterson wrote:
[color=#0000FF]myxlpyx[/color] wrote:
I'm sure I have once seen a rainbow forming a circle around the sun, rather than in the opposite direction to the sun as is common. The sun was high in the sky, there were clouds in the sky and I think it was raining very slightly. Has anyone else ever seen this before, or can I not trust my memory anymore?
It was certainly not a rainbow. There are a number of halo effects that can be seen around the Sun, and some have associated (rainbow-like) color, although usually less saturated than a rainbow. The optical mechanism for these halo effects is different from that of a true rainbow.
It was almost certainly not a rainbow.
http://en.wikipedia.org/wiki/Rainbow wrote:
<<A third, or tertiary, rainbow can be seen on rare occasions, and a few observers have reported seeing quadruple rainbows in which a dim outermost arc had a rippling and pulsating appearance. These rainbows would appear on the same side of the sky as the Sun, making them hard to spot. One type of tertiary rainbow carries with it the appearance of a secondary rainbow immediately outside the primary bow. The closely spaced outer bow has been observed to form dynamically at the same time that the outermost (tertiary) rainbow disappears. During this change, the two remaining rainbows have been observed to merge into a band of white light with a blue inner and red outer band. This particular form of doubled rainbow is not like the classic double rainbow due to both spacing of the two bows and that the two bows share identical normal colour positioning before merging. With both bows, the inner colour is blue and the outer colour is red.

Higher-order rainbows were described by Felix Billet (1808–1882) who depicted angular positions up to the 19th-order rainbow, a pattern he called "rose". In the laboratory, it is possible to observe higher-order rainbows by using extremely bright and well collimated light produced by lasers. A sixth-order rainbow was first observed by K. Sassan in 1979 using a HeNe laser beam and a pendant water drop. Up to the 200th-order rainbow was reported by Ng et al. in 1998 using a similar method but an argon ion laser beam.>>
..............................................................................................................................................
<<It has been suggested that rainbows might exist on Saturn's moon Titan, as it has a wet surface and humid clouds.
The radius of a Titan rainbow would be about 49° instead of 42°, because the fluid in that cold environment is methane instead of water.
A visitor might need infrared goggles to see the rainbow, as Titan's atmosphere is more transparent for those wavelengths.>>
Art Neuendorffer

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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by Beyond » Sun Aug 08, 2010 7:51 pm

alter-ego wrote:
beyond wrote: All viewpoints have their part in the overall scheme of things. But the fringe that i spoke of needs no photons. It has it's own light, so it is not a misperception to say that there are no photons there. However, photons are needed here to be able to see Rainbows and Apods and things. :D
Of course. I was also trying to provoke thoughts beyond the immediate technical discussion, and it was your reply that prompted mine.
Thats ok, but Apod is a very scientific forum and we really should try not to go off topic much. In my case, i don't know how to start a new thread so i most likely won't be posting in Apod much any more, but still looking a lot!!
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by neufer » Sun Aug 08, 2010 8:47 pm

beyond wrote:
Thats ok, but Apod is a very scientific forum and we really should try not to go off topic much. In my case, i don't know how to start a new thread so i most likely won't be posting in Apod much any more, but still looking a lot!!
So I am basically stuck now with a whole caseload of unused Hostess SNO-BALL puns. :|
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by tishg » Sun Aug 08, 2010 9:58 pm

This is great image of a rainbow. Would you allow me to use it with a resource I am writing for Te Kura/The correspondence School of NZ?
We have rainbows like this in Wellingon evenings at certain times of the year, but I don't have the ability to photograph the whole span. They usually appear on the back end of a 'Wellington southerly' in unstable air.

While I'm here - we are looking forward to 12-13 Aug when there is a conjunction of the inner planets and the moon. Hoping for clear skies. I walked out of the Carter Obervatory (Wellington) last week at about 1830 NZST, to see Mercury, Venus, Mars and Saturn clearly. This immediately after a free ride round the solar system and some other planets, courtsey of Carter's new planaterium. Well worth a visit for anyone coming to Wellington,

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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by bystander » Mon Aug 09, 2010 1:33 am

tishg wrote:This is great image of a rainbow. Would you allow me to use it with a resource I am writing for Te Kura/The correspondence School of NZ?
You would have to contact the copyright holder, Bernd Thinius (Inastars Observatory Potsdam), for permission to use the image.

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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by Beyond » Mon Aug 09, 2010 2:52 am

neufer wrote:
beyond wrote:
Thats ok, but Apod is a very scientific forum and we really should try not to go off topic much. In my case, i don't know how to start a new thread so i most likely won't be posting in Apod much any more, but still looking a lot!!
So I am basically stuck now with a whole caseload of unused Hostess SNO-BALL puns. :|
Just so you won't be burdened with the concern that that caseload of active Sno-Balls will go off in your face(you should be so lucky)there is a lot more to this site than Apod. Feel free to lob one here and there as the pun fits. Toodle-Looo
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by bystander » Mon Aug 09, 2010 2:51 pm

beyond wrote:In my case, i don't know how to start a new thread
Starting from the Board Index, select the forum in which you wish to start a new topic (thread) and click on the NEWTOPIC button at the top (or bottom) of the page.
beyond wrote:so i most likely won't be posting in Apod much any more
It certainly didn't seem to slow you down very much in the past. :wink:

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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by Beyond » Mon Aug 09, 2010 3:54 pm

Yes - the past. Thats what we cause as we time travel to the future - which is a present - that degrades and becomes passe' and dies and becomes the past,from which we time travel to the present from........
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Re: APOD: Rainbow at Sunset (2010 Aug 07)

Post by Iloverainbows » Tue Aug 10, 2010 10:46 am

It's starting to look like a triple rainbow!