Rainbows

Hi,

Caught a very nice rainbow last night between the showers in Santry. Second bow was very clear and the primary had very vibrant colours.
However I noticed that the primary appeared to have an extra green and purple band on the inside of the arc. So you had:
red:orange:yellow:green:blue:indigo:violet:green:violet

My girlfriend saw it too so it wasnt just me seeing things!

Has anyone else seen this before or got an explanation?

Cheers,
~Al

Funny you should say that Albert, would you believe i saw the same phenomenon last week!! I can't explain it, i had never seen anything like that before, ever!! I thought that all rainbows consisted of (r,o,y,g,b,i,v)
only - Strange indeed!!!
Keith......

hi Al and Keith,

yes, I saw the rainbows too and they were quite dramatic. re: the queries on the colour sequence, here goes on a quick account of bows!!!

as everyone knows, a rainbow is the result of the simple interaction of sunlight and water in droplet form. A "prism" effect causes a ray of light to be split into various colours corresponding to a different wavelength of light and each is reflected at a particular angle from the opposite wall of the drop. This is how we get the grading of the colours in a bow.

the phenomenon of "interference patterns" gives rise to an occasional overlap of the colours making it look as if the outer edges of a bow has a number of other rainbows superimposed on it. In fact, the proper term for these are "supernumerary arcs" -- not to be confused with an actual secondary bow!

looking at a rainbow too you may be struck by how the sky inside a bow can occasionally appear brighter than outside. This is due to the preferential scattering of the light within the water droplets back towards the red end of the spectrum. If a secondary bow accompanies the primary then the colours are reversed and the scattering is towards the outside of the bow. This can lead to what looks like a dark band of sky between both bows which is dubbed Alexander's Dark Band after a Greek philosopher who described the phenomenon 2,000 years ago.

the classic book on the subject is by Robert Greenler and is called "Rainbows, Haloes and Glories" while Marcel Minnaret's "Light and Colour in the Outdoors" is very detailed but can be expensive.

an interesting web link is;

www.sundog.clara.co.uk/atoptics/phenom.htm

while we can only drool over the fantastic images by Pekka Paravininen at www.polarimage.fi

regards,

John F.

the classic book on the subject is by Robert Greenler and is called "Rainbows, Haloes and Glories" while Marcel Minnaret's "Light and Colour in the Outdoors" is very detailed but can be expensive.

S&T this month have a review of another book on the topic.
"Out of the blue" by John Naylor, ISBN 0521809258 $35


Might be of interest.

Cheers,
~Al