‘Is a “fogbow” a thing?’ asked Elaine Booth (Member 63,806), who came across this phenomenon while walking her dogs in the early morning mist near Hungerford, West Berkshire, England.  

Yes, Elaine, there are such things as fogbows. They are like ghostly versions of rainbows. They form when sunlight shines from behind you onto tiny droplets of fog rather than the much larger raindrops that cause rainbows. The sunlight shines through the fog droplets and bounces off their inside backs, just like it does when raindrops form rainbows, but the tiny size of the fog droplets has the effect of blurring the resulting arcs of light. At less than 0.1 mm across, the fog droplets are so small as to bend, or diffract, the sunlight shining around them. This means that instead of the bold and distinct colours of a rainbow, the fogbow’s colours overlap and blur, giving the effect a pale, phantom-like appearance. These ghosts of the low atmosphere are, Elaine, very real indeed.