Wednesday, October 14, 2020

Rainbows: Beyond the Arch

rainbowRainbows require two things: sunlight, and water. Rainbows can be seen not just in the rain but also in the mist, spray, fog, and dew. 

The best place to consistently find both of these things and spot a complete rainbow, is a tall mountain or ridge where it is or has just rained, making the Adirondack high peaks an amazing place to view this natural wonder. A rainbow is a meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets resulting in a spectrum of light appearing in the sky.  Similar to a mirage, a rainbow is formed when light rays bend, creating an effect that is visible, but not able to be touched or approached. 

Half an image

Many people who see rainbows are not seeing it completely, rather they are seeing the upper top half. Rainbows are really whole circles, only seen fully from a location higher than the horizon.  The circle (or half-circle) results because there is a collection of suspended droplets in the atmosphere that are capable of concentrating the dispersed light at angles of deviation of 40-42 degrees relative to the original path of light from the sun. These droplets actually form a circular arc, with each droplet within the arc dispersing light and reflecting it back towards the observer in rays of red, orange, yellow, green, blue, indigo and violet.  Rainbows are stunning, like shooting stars and Northern lights, they are momentary magnificence, Mother Nature style.

The rainbow order

There are numerous types of rainbows which undergo different processes in their formation.  A rainbow order is a characteristic which is used to categorize rainbows into the two basic groups: primary rainbows and secondary rainbows. The main determinant of a rainbow order is the number of reflections of light in water droplets involved in the formation of a rainbow. Primary rainbows are also known as first-order and are formed from one light reflection, while secondary rainbows, also known as second-order rainbows, are made of two reflections.

There are other rainbows which are formed from more than two internal reflections, and these are known as higher-order rainbows. The number of internal reflections is not limited and runs to infinity, but the higher-order rainbows become less visible as the number of internal reflections increase. 

Rare occurrences

Twinned rainbows are some of the rarest types of rainbows to occur in nature. These rainbows start from a common base but split along the arc, making a primary rainbow and a secondary rainbow with the two having colors appearing in the same order. The color profile in twinned rainbows is the same spectrum as that in a regular rainbow. 

Twinned rainbows are formed when the light is refracted after coming across two rain showers which have distinct sizes of raindrops. The sizes of raindrops in the two rain showers are usually 0.40 millimeters and 0.45 millimeters with the small variation in size being the cause of the splitting of the rainbow into two. In some instances, the rainbow can even split into three branches, but such occurrences are extremely rare.

Multiple rainbows are another type of rainbow which is also a rare occurrence. Multiple rainbows are sometimes referred to as double rainbows. As the name suggests, multiple rainbows are instances when more than one rainbow occur simultaneously in the same place and are made up of a primary rainbow and other secondary rainbows. The region in-between the multiple rainbows which is unlit is officially known as Alexander’s band, named after Alexander of Aphrodisias, a 2nd-century Peripatetic philosopher who first described the band. Multiple rainbows are formed by the double reflection of sunlight inside raindrops and are between 130 degrees and 127 degrees in width. The reflection of white light takes place inside the colored bands of the rainbows.

Another rare type of rainbow is the supernumerary rainbow. This rainbow appears as an extra band inside the primary rainbow or in some cases, outside the secondary rainbow and normally occurs in fogbows. Supernumerary rainbows are detached from the main bow known as the stacker rainbow, and as they move away from the main bow, they become fainter. Supernumerary rainbows are formed as sunlight strikes small droplets of water, usually having a diameter not exceeding 1 millimeter. One distinct feature of supernumerary rainbows is that they are made up of pastel colors instead of the normal spectrum present in the usual rainbow.

A monochrome rainbow is a type of rainbow whose color spectrum is based on a single color, usually red. Also known as a red rainbow, a monochrome rainbow is a rare meteorological occurrence and only happens when sunlight travels farthest through the earth’s atmosphere, during sunrise or sunset. Due to the great distance, short wavelength lights such as yellow, blue and green are scattered and displaced from the spectrum leaving only the red color. A monochrome rainbow has quite a dramatic effect on the atmosphere.

A reflected rainbow and a reflection rainbow are two distinct types of rainbows, but both are closely related. A reflected rainbow occurs after sunlight is deflected from droplets of rainfall and then reflected from a water body before being viewed by an observer. Reflected rainbows are sometimes visible on the surface of the water below the horizon and can be viewed (albeit partially) in bodies of water as small as puddles. A reflection rainbow, on the other hand, is formed when sunlight is first reflected off a body of water, then deflected by raindrops before being visible to an observer. Reflection rainbows are rarely visible due to the complexity involved in their formation.

Moonbows and fogbows

Rainbows are thought of being a result of the reflection and deflection of sunlight on water droplets. However, in some instances, rainbows can also be formed under moonlight, but such instances are extremely rare. Nonetheless, on the few occasions when rainbows under moonlight are formed during a full moon or a near equivalent. These rainbows which are also known as moonbows are thought to display a single color but are made up of a spectrum of different colors, but due to the dullness of moonlight in comparison to sunlight, these colors are not visible to the naked human eye.

A fogbow is a special type of rainbow which is formed as sunlight travels through a small cloud or fog and the fog droplets diffract the sunlight. The color spectrum in a fogbow is usually white, red and blue. Fogbows are usually formed over a body of water or in an area with thin fog.

No matter what type of rainbow you are fortunate enough to see, they are painted across the sky as a reminder of how amazing and magical the wonders of nature are. 


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Jackie Woodcock was born and lives in the Adirondack Mountains. She is an apiarist, lepidopterist, conservationist, teacher, writer, artist, and a co-owner of SkyLyfeADK. You can find her SkyLyfeADK on Instagram and Facebook.


3 Responses


    In a double rainbow the second rainbow has the colors reversed.

  2. Steve Sehnert says:

    This past summer in July on Limekiln Lake I saw one of the most interesting and beautiful rainbows I have ever seen. One afternoon partial rainbows were forming across from our camp. Only the right hand portion and very bright. Suddenly one formed that came right down to the water and you could see through it. It was maybe a thousand feet away. You could see the trees etc. on the ridge on the back side of it and very clearly. It was very transparent and almost looked artificial. Couldn’t get my camera fast enough as it didn’t last long. Hope to see that again some day.

  3. Balian the Cat says:

    I am curious why rainbows always seem appear in the same place? Is it geography, perspective, time/location of the sun?

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