Jakob Owens / Unsplash
Nature has been known to create some pretty cool visuals but a circle rainbow is in a league of its own.
The rainbow is one of the most beautiful natural phenomena that can be seen with the naked eye as it forms in the sky. Celebrated in photos, music, and film Judy Garland sang about going over the rainbow back in the 1939 movie The Wizard of Oz.
The rainbow has since become synonymous with the promise of beauty and excitement through life. The magical presence of a rainbow is a sight that is deemed to be lucky. In some more spiritual communities, they are sometimes seen as good omens, as well as the promise of rebirth and peace.
The different colors of the rainbow make up a spectrum of colors including red, orange, yellow, green, blue, indigo, and violet spectrum of colors that are used to create every color known to man.
The beauty of a full circle rainbow is one that most people won’t get the chance to see in their lifetime because of how rare it is to actually get a glimpse of one. The conditions, the vantage point, and the location of the sun in relation to the ground are all factors that will come into play when getting a glimpse of the elusive beauty of a circular rainbow. But is the round rainbow that rare or is the regular half-arch rainbow just a percentage of the optic illusion that’s there?
How is a rainbow formed?
For a rainbow to form in the sky, conditions have to be perfect. This usually happens after a very heavy rainfall or storm system when the sun moves through the sky and clouds. The light of the sun against the number of water droplets in the air leftover from the store cause a few different processes to happen, all of which contribute to the creation of the rainbow. The first step in this process is called reflection. When the sun shines into the rain, it enters the water droplets. When this happens, it bounces around inside the droplet and then reflects out off the beads of water.
The second step in the process is refraction. After the sun’s rays are reflected out of the raindrop, the rest of the light that goes through the water is then refracted—when the light that enters becomes bent on its way out. This refraction happens more than once, too.
When this happens, the white light is then turned into the different colors of the rainbow through a process called dispersion.
Dispersion occurs when the spectrum of colors in white light exits the raindrop, separating at different speeds. Each color separates at its own speed, which is the exact reason they have their own personal hue. This entire process has to occur perfectly so that the colors reflect at the correct angle thus allowing the rainbow to become visible to the naked eye.
What are full circle rainbows?
Technically speaking, all rainbows are circle rainbows, although most people will only ever get the chance to see the arch view of a rainbow up close in their lifetimes. It might be hard to believe because it’s so rare to spot a full-circle rainbow, but when a rainbow forms, it does so in a full circle because of the critical angle it needs to obtain before being visible.
The reason why the eye only sees the arch of the rainbow is that the other half is generally blocked by the horizon, thus unable to be seen. The amount of the rainbow seen is entirely dependant on where the sun is located in the sky. When the is low in the sky that usually means that the rainbow will be higher in the sky.
What makes a round rainbow unique?
The process that makes a rainbow possible doesn’t change because the conditions need to be so perfectly met for it even to occur. The difference between a full circle rainbow being visible and the arch that is regularly seen depends solely on what angle the rainbow is seen from.
The higher up you are, the more likely it is that the horizon won’t block your view and you’ll get the chance to take in the phenomena. People that climb mountains often see more circular rainbows in the right conditions because they have a better view. Pilots are often lucky enough to see circular rainbows because of their location in the sky and the vast view they have from the pilot’s chair.
The exact conditions needed to spot a rainbow
Light moves through different objects at different speeds. For example, when light travels through the air, it goes at 300,000 kilometers per second. Through water, though, it travels at only 225,000 kilometers per second. This slowing down of the light helps the light go through the process of refraction as mentioned above.
To be able to see the entire rainbow, having a high vantage point is the only way to get a full glimpse without the ground distorting what you’re seeing.
To see the rainbow, you have to look away from the sun or else the process will be missed and you won’t get to witness the phenomena. To be able to see the entire rainbow, having a high vantage point is the only way to get a full glimpse without the ground distorting what you’re seeing. Also, since the prism of color is affected by the curtain of light in the droplet, you will only see one color per drop—if you’re lucky.
Why does the ground have so much to do with it?
The ground acts as a light absorber when the rainbow hits it. The circular part of the rainbow is still there because the process doesn’t decide the shape of the rainbow, just whether or not it’s visible. When the bottom of the rainbow hits the ground, it disappears out of sight.
This is because the horizon ends up distorting the rest of the rainbow and limiting how many raindrops are within your line of sight, and as it stands, the more raindrops you can see, the better and more pronounced the rainbow will be. Your perspective of the rainbow depends entirely on how far away from the sun you are.
Circle rainbows around the world
In 2014, one famous instance of a circular rainbow being seen happened in St. Petersburg, Russia. Construction workers were just getting on with their day at Lakahta Centre after a storm hit and from the top of the high crane, the placement of the horizon against the sun made the conditions perfect to spot the full circle rainbow.
Another amazing instance of a circular rainbow happened in The Bay of Islands in New Zealand in 2017. A skydiver by the name of Anthony Killeen lept from a plane and on his way down managed to capture the rare sighting of the circle rainbow on a GoPro on his way down.
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