VIBGYOR is quite possibly the most known acronym worldwide. Rainbows are a mesmerising treat for the eyes. They have us spellbound with their charm no matter how many times we see them. It is probably the only naturally occurring phenomenon that enables us to see multiple colours at once.
But, can rainbows also be of a single colour?
In 2016, a photographer based in the UK, Melvin Nicholson, captured the rarest sight of a pure white light arch in Scotland. It was not like white rainbows were not a thing before but this one was the most recent proper sighting. White rainbow, or “fog bow”, they called it.
WHAT EXACTLY IS IT?
According to NASA:
The fogbow’s lack of colors is caused by the smaller water drops … so small that the wavelength of light becomes important. Diffraction smears out colors that would be created by larger rainbow water drops..
A fog bow, or a white rainbow, is obviously a similar phenomenon to a rainbow. But like the name suggests, it appears as a bow in fog and not in rain. Like rainbows, fogbows can be seen when the sun is at your back. When a fog bow appears at night, it is called a lunar fog bow.
GETTING INTO THE SCIENCE BEHIND IT
Violet light bends the most, red least. So red light is angled more steeply towards the ground than other colours. This means that red light leaving water droplets higher in the sky has a better chance of reaching your eyes. This is why we see rainbows as bands of colours with red on the outside.
Fogbows are formed when sunlight meets moisture, refracting light from the tiny water droplets suspended in the air. While rainbows mostly appear after rainfall, as sunlight refracts through larger water droplets, fog bows show up when the sun shines on fog, consisting of much smaller water droplets.
“Due to the small size of the droplets, the light waves don’t spend enough time within the droplets to refract enough to separate cleanly and focus into colours,” US National Weather Services meteorologist Brian Jackson explained.
Unlike water droplets during rain, fog particles of water act as much smaller prisms. They can’t refract as much light but allow light to diffract from the small droplets and merge into a circular white haze as the colours continually overlap each other.
According to The Weather Channel, the best condition for spotting a fog bow is on a slightly foggy day, with bright sunshine on your back, around areas likely to gather humidity like a field, a mountain valley, at a coast, or on a lakeshore.