http://www.slip.net/~vdinets/rainbows.htm
 
BlackHills
Evening rainbow, Black Hills, USA

Rainbows
All rainbows are beautiful, but very few of them are bright enough to look good on photos. Here are some of the best (or unusual) rainbows I have seen. 
Badlands
Double rainbow,
Badlands Nat. Park, USA 
Crow Indians called the Great Plains "the country of big sky". It is one of the World's best places to watch thunderstorms and rainbows. I took this picture few minutes after a very strong June thunderstorm (HP supercell) with lots of rain, hail and wind. There were no tornadoes, but after the cloud had passed, I was awarded with such a beautiful sight.
Rainbows are less common in tropics, because the sun is too high overhead most of time. Still, if you are in the mountains, you sometimes can see the rainbow by looking downhill. This unusually bright rainbow was visible for almost an hour during winter shower. Oahu
Winter rainbow, Oahu, Hawaii
Chilie
Small rainbow,
Carretera Austral, Chilie 
South from the tropical latitudes, rainbows become common again. This tiny one appeared after a spring snow/rainstorm in Southern Chilie. It was only visible for less than one minute.
When the sun is very low, the atmosphere sometimes filters away all colors, except for red, as can be seen in this pink rainbow. This kind of rainbows is very rare, and they usually turn into multi-colored rainbows in less than one minute. Iguazu1
Monochromatic rainbow, Iguazu, Argentina
Iguazu2
Multicolored rainbow, Iguazu, Argentina
As the sun rises higher, the rainbow quickly becomes multicolored and much brighter. On this picture, taken few minutes later, yellow and green colors are already in place, but blue is still weak
Finally, about 30 minutes after sunrise, the sunlight gains all colors, and rainbows become complete with blue and purple. In the middle of the day, the tropical sun is high overhead, and the rainbows you can see in large waterfalls are sometimes very bright and beautiful. Iguazu3
Triple rainbow, Iguazu, Argentina
Niagara
Moonlight rainbow,
Niagara Falls, USA
To see moonlight rainbow (also monochromatic), you need dense clowds of water droplets - such as in high surf or large waterfalls. Very rarely it can be observed in the sky after rain, but in this case it is not so bright. Street lights can also produce small yellow rainbows.
This rainbow was hovering inside a small, vapor-producing crater in the middle of very dry lava desert. The colors were unusual, because some wave lengths were absorbed by volcanic gases. Beside the rainbow, the crater was inhabited by endemic moist-loving ferns and millipeds. crater
Rainbow in volcanic crater,
Isabela, Galapagos Islands
fullcircle
Sunset rainbow, Napa Valley State Park,
California (composition of 4 images)
This was the most beautiful rainbow I have ever seen. It was raining heavily all day, and it was already dark in the forest, so this rainbow was a complete surprise. It was almost full circle, because I watched it by looking in a valley from a mountain top; outside this circle everything was dark, and inside there was still bright light from the setting sun...
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