A rare white rainbow caused a spectacle after it appeared over Crowdy Head in New South Wales.
It had many asking, what exactly is it?
The white rainbows are technically called “fogbows” which form when sunlight interacts with water inside a fog rather than raindrops.
What is a white rainbow?
The Bureau of Meteorology’s Jonathan How said fogbows are similar to rainbows.
“You still have the same processes going on with the sun behind you and then the fog or the rain in front of you,” he said.
“But the main difference is the size of the water droplets within the actual bow itself.
“For a fogbow, water droplets in fog are very, very small whereas water droplets in a rainbow are much larger.”
How said the tiny size of the droplets affects the colour and gives it a white appearance.
“That affects how the light is scattered and how we see it,” he said.
“The smaller the droplet, it looks white. That fogbow looks quite diffused and very wispy.
“The bigger the raindrop, the more defined and stronger the colours of the rainbow are.”
How rare are white rainbows?
They are definitely more rare than typical rainbows, How said.
“Generally with fog, you need just the right conditions,” he said.
“Sometimes, you can be shrouded in fog and then it clears but then you don’t really see any fogbows and that’s because you need to have the fog clearing with the sun behind you, which doesn’t always happen, and you might not be in the right spot.
“Whereas rainbows are much more sort of common phenomena so they are pretty rare.”
The best chance to catch a glimpse of a fogbow is in wintertime.
”As the sun rises and the fog starts to clear and lift, that’s the best chance of seeing a fogbow,” How said.
“Everything needs to line up.”
How many types of rainbows are there?
There are several types of rainbows, like double and triple rainbows.
How said that while fogbows aren’t classified as a rainbow, it has similar optics.
“No less spectacular, I would say, even though they’re not colourful they’re pretty cool,” he said.
