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Natural Science Forum / Physics / Optics / May 2005sundogs vs rainbows
would someone please explain why the innermost visible color ring of a sundog is red while that of a rainbow is violet? The only consistancy I can think of is that the ring closest to the sun has the longest wavelengths. thanks Lyle > would someone please explain why the innermost visible color ring of a > sundog is red while that of a rainbow is violet? The only consistancy I > can think of is that the ring closest to the sun has the longest > wavelengths. thanks > Lyle It's because the rainbow involves a reflection inside the water droplet. In a sundog, the light comes towards you, enters the droplet is refracted some as it does so, then exits the droplet towards you, being refracted again as it does so. Very much like how a prism works. In a rainbow, the light goes in, is reflected on the backside, then comes out more-or-less back towards the light source. The reflection is what reverses the order of colors relative to the sundog. An excellent depiction of a rainbow plus the secondary bow: http://en.wikipedia.org/wiki/Rainbow A diagram of sundogs: http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/ice/sd.rxml Some more starting points for learning about these and other atmospheric optical phenomenon: http://www.engl.paraselene.de/html/parhelic_circle.html http://www.meteoros.de/indexe.htm http://www.sundog.clara.co.uk/resource/indx.htm Brian  Signaturehttp://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism Home of the Seismic FAQ http://www.skywise711.com/SeismicFAQ/SeismicFAQ.html Sed quis custodiet ipsos Custodes? I thought the solar halo was from water droplets and the sun dogs were due to hexagonal ice crystals but I might have it backwards. Jim Klein "West Coast Engineering" >I thought the solar halo was from water droplets and the sun dogs were > due to hexagonal ice crystals but I might have it backwards. You are correct. Sundogs (A.K.A. parhelia) are caused by refraction inside hexagonal ice crystals floating nearly horizontally, i.e. parallel to the ground. Martin SignatureM.A.Poyser Tel.: 07967 110890 Manchester, U.K. http://www.livejournal.com/userinfo.bml?user=fleetie > I thought the solar halo was from water droplets and the sun dogs were > due to hexagonal ice crystals but I might have it backwards. > > Jim Klein Whoops on me....shouldn't have said "drops" when I was referring to the sundog scenario. But the basic idea still remains. The sundogs are due to all refraction whereas the rainbow involves a reflection in addition to the refractions. Brian Signaturehttp://www.skywise711.com - Lasers, Seismology, Astronomy, Skepticism Home of the Seismic FAQ http://www.skywise711.com/SeismicFAQ/SeismicFAQ.html Sed quis custodiet ipsos Custodes? Thanks all, great ray tracings in the article. Funny I once saw a beautiful supernumary rainbow and photographed it and convinced myself that it must just be internal reflections in the camera lense. now I know better. Thanks Lyle >> I thought the solar halo was from water droplets and the sun dogs were >> due to hexagonal ice crystals but I might have it backwards. [quoted text clipped - 7 lines] > > Brian In the wikipedia article links to supernumerary rainbows (see http://www.jal.cc.il.us/~mikolajsawicki/rainbows.htm these are not secondary rainbows, as the supernumerary bows seem are directly adjacent like they are connected to the inside of regular rainbows and are rare) show good examples of the difference between the two. They also say that supernumary rainbows can only be explained by the wave nature of light: " Supernumerary rainbows provide a strong indication of the wave nature of light. In fact, it was a mystery of supernumerary rainbows that prompted Thomas Young to do the famous double-slit experiment in 1801 that confirmed the wave nature of light and led to his explanation of supernumerary rainbows in 1803. " Can anyone briefly explain this? thanks Lyle >> would someone please explain why the innermost visible color ring of a >> sundog is red while that of a rainbow is violet? The only consistancy I [quoted text clipped - 29 lines] > > Brian Different light paths through the obscuring water. Also note that there is sometimes another rainbow inside of the typical one that you see and it is reversed from the brighter one. That there is a rainbow as color is rather obvious. -- Why isn't there an Ozone Hole at the NORTH Pole? > Different light paths through the obscuring water. Also note that there is > sometimes another rainbow inside of the typical one that you see and it is [quoted text clipped - 3 lines] > -- > Why isn't there an Ozone Hole at the NORTH Pole? Secondary bows are OUTSIDE the primary bow. There are even tertiary bows outside the secondary bow. I may have seen one very dimly once. Bill You're right. It has been so long since I've seen a good rainbow (they don't seem to want to show up around here where I live) that I've forgotten the relationship. -- Why isn't there an Ozone Hole at the NORTH Pole? |
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