One of the most beautiful visual phenomena that occurs when it stops raining is the rainbow. A rainbow is an optical phenomenon that occurs when sunlight passes through water droplets suspended in the atmosphere. However, on some occasions a double Rainbow.
In this article we are going to tell you why a double rainbow is formed, what its characteristics and fundamental aspects are.
Rainbow formation
The formation of a rainbow involves several steps:
- Refraction: White light from the sun, which is actually made up of a mixture of colors, enters a drop of water. Upon entering the drop, the light bends or refracts due to the difference in the speed of light in air and water.
- Internal reflection: Inside the water droplet, light reflects off the inner walls of the droplet. This reflection causes the light to break down into its individual colors due to dispersion, separating the colors of the visible spectrum, like a prism. If you'd like to delve deeper into this topic, you can read more about the Newton's prism.
- Refraction again: After internal reflection, light leaves the water drop and is refracted again as it passes from water to air. Light emerges at specific angles, depending on its wavelength. This causes the different colors to separate even more.
- Rainbow formation: Rays of light separated into colors spread out in a circular pattern, creating what we know as a rainbow. The rainbow appears as a semicircle in the sky due to the shape of the water droplets that act as natural prisms.
It's worth mentioning that light is actually reflected and refracted within multiple water droplets in the atmosphere, and each contributes to the formation of the rainbow we see. The rainbow is a spectacle of colors due to the decomposition of white light into its individual components: red, orange, yellow, green, blue, indigo, and violet. Furthermore, these beautiful optical phenomena have similarities to other visual effects, such as the moon rainbow.
Rainbows are undoubtedly the most recognizable natural phenomenon, They form when sunlight passes through water droplets during rain. The scattered light is divided into a spectrum of colors, similar to a prism. To observe a rainbow, specific conditions must be met: the presence of both rain and sunlight, and the observer must stand between the two with the sun behind and the rain in front. Additionally, light must reflect at a 42º angle onto the droplets, so they are rarely seen during midday and usually appear during rainy mornings and afternoons.
Double Rainbow
When the white light beam enters a droplet, its various colors are dispersed at different angles. Due to this phenomenon, white light is refracted and we can discern the individual colors that make it up. The red tone is the one that curves the least, while the other colors curve more and more until they reach violet. Thus, the beam of white light is transformed into a collection of rays, each of which exhibits a different color that diverges as it travels within the drop. These rays then encounter the inner surface of the drop and are partially reflected back, as if the drop's surface were a mirror. The rays encounter the surface of the drop once more before exiting, and each one now has a different angle and color. This process, repeated in countless drops, is what produces the different arcs of color that combine to form a rainbow. To better understand this phenomenon, you could explore how light behaves in other contexts, such as in double stars.
When light refracts and reflects off water droplets, a beautiful phenomenon known as a double rainbow occurs. This event is characterized by two arches of different colors, the inner arch being more vivid than the outer one. The colors of the double rainbow, in order, are red, orange, yellow, green, blue, indigo and violet. The double rainbow is a rare occurrence, but when one is lucky enough to witness it, it is truly an impressive spectacle of nature.
Sometimes not one but two rainbows may appear, with the colors in different arrangements and one on top of the other. The second rainbow is created when sunlight penetrates the bottom of a raindrop and then bounces inside it twice before reaching our eyes. Due to the two bounces, the light waves cross and leave the drop in the opposite order to that of the primary rainbow. This secondary rainbow is less vibrant because some of the energy is dissipated with each bounce. The variability of these visual phenomena can be related to other events in the atmosphere, such as sea storms.
When light rays bounce off raindrops twice, they cover a greater distance, resulting in a greater exit angle. That is why the second rainbow is perceived to be higher than the first. Additionally, the colors of the second rainbow will appear in reverse order: red at the bottom and purple at the top.
Alexander Bands
We are referring specifically to the portion of the sky that is visible between rainbows, rather than a musical ensemble. This area, known as Alexander Bands, It is clearly darker than the rest of the sky and is located between the primary and secondary rainbows.
The primary rainbow or the sky within it is made up of rays of light that undergo a single reflection from raindrops. Meanwhile, the secondary arc or outer sky is formed by rays that have been reflected twice and are deflected. The regions of the sky where raindrops are present along the sight lines between the two arcs cannot reflect all the light to the observer's eye. As a result, these areas appear darker. In 200 AD, Alexander of Aphrodisias was the first to describe the phenomenon that now bears his name.
I hope that with this information you can learn more about the double rainbow and its formation.