Weather Wednesday: Fogbows

FARGO, ND — If you ever stumble across a strange arc that looks like a colorless rainbow, it's not a ghost, but it is a ghost rainbow —more commonly known as a fogbow. This optical phantom phenomenon occurs in a similar fashion to rainbows. When the sun is at your back and low in the sky, sunlight bounces around inside water droplets and reaches our eyes in the form of a large circle, or more often thanks to the ground, a half circle. But whereas rainbows are inherently colorful, fogbows are not. That s due to the difference in size of the water droplets. With rainbows, the rain droplets are generally around one millimeter in width. When sunlight hits these larger drops, it refracts the light, spreading it out into the full spectrum of colors, resulting in a rainbow. For fogbows, the water droplets within the fog are very small, around 50 micrometers wide. This tiny size means that sunlight gets diffracted instead. Diffraction results in the li