When spotting a rainbow, we’re used to seeing its familiar seven-colour display.
But colourless rainbows, while uncommon, can also form in the sky.
Natalie Penney was taking her garbage out in Barss Corner, N.S., Monday morning and was surprised to see what she first described as a “rainbow in mist,” noting she does not recall seeing one before.
What Natalie captured is a fogbow, sometimes referred to as a white rainbow or ghost rainbow.
The process in which a fogbow forms is very similar to a rainbow.
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Recall that rainbows form when sunlight entering raindrops slows, bending and changing its direction through the process of refraction. This separates the colours in the visible light spectrum and reflects them out of the droplet.
The same process occurs with fogbows, except the water droplets found within fog are remarkably smaller than rain droplets — as much as 1,000 times smaller in some cases.
The size difference means the smaller droplets can’t refract or reflect as much light, which is why fogbows appear faint or white.
In some cases, a fogbow may display faint colours on the outer and inner edges of the bow. Otherwise, you will see something like what Natalie captured in Nova Scotia.
While fogbows are generally considered by some as uncommon or rare, given the amount of fog much of Atlantic Canada experiences each year means your chance of seeing one is often greater.
Have a weather question you would like answered? Send your weather photos and questions to: weather@saltwire.com.
Allister Aalders is a weather specialist with SaltWire Network. Reach him at allister.aalders@saltwire.com
