photo #7965145

With her back to the rising Sun, Diana Bishop (Member 64,329) spotted this fogbow on a morning winter walk near Exeter, Devon, England. Fogbows are like rainbows formed by tiny cloud droplets rather than raindrops. Just like with rainbows, the sunlight shines through the water particles, reflecting off their inside surfaces back towards the viewer. Rainbows have bright colours because of the way the light bends, or refracts, as it shines into and out of the raindrops, which act rather like little spherical prisms. But fogbows have only very faint colours, if any at all. Often they appear, like Diana’s one, as just a ghostly white. The tiny fog droplets, each far less than a hundredth of a millimetre across compared to the 2 mm or so of a raindrop, have an added effect on the sunlight. Being so small, they also scatter, or diffract, the light much more than raindrops do. This has the effect of blending back together the spectrum of colours that you’d see were it a rainbow, blurring them into a subtle and diffuse arch of white. In other words, fog is less showy with its bows than rain.