Rainbow – Concept, types, formation and why its 7 colors

We explain what a rainbow is and the types of rainbows there are. How it is formed, why it has seven colors and the places with the most rainbows.

In the most intense manifestation of a rainbow, its seven colors can be appreciated.

What is a rainbow?

The rainbow is a meteorological phenomenon and is presented in the form of an arc of multicolored light, by the refraction of sunlight (white light) in the raindrops that are suspended in the atmosphere. In its most intense manifestation, the seven colors can be seen: red in the upper or outer part and successively orange, yellow, green, cyan (or turquoise), blue and purple in the lower or inner part.

Types of rainbows

Double Rainbow
The arcs of a twin rainbow originate from a base point and their colors are not reversed.

The types of rainbows depend on different atmospheric conditions that influence the projection mode of the luminous arc, and among the main ones, the following stand out:

  • Primary rainbow. It is the best known and usually appears after a storm or in sloping areas of splashing water, such as a waterfall.
  • Secondary rainbow. Also called a “double rainbow,” it forms above the primary rainbow, with the colors reversed.
  • Supernumerary rainbow. It is rare to see and consists of the projection of several faint rainbows simultaneously, product of the diffraction of sunlight.
  • Red rainbow. Also known as a “monochrome rainbow,” it forms after rain and during sunrise or sunset, with the sun set very low or close to the horizon.
  • Circumhorizontal arc. Also known as “rainbow of fire”, it appears very rarely and is formed from small drops of water in cirrus clouds, where the spectrum of colors is projected (instead of appearing in the shape of an arc).
  • Twin rainbow. It is very rare to see and is projected with two arcs that, unlike the secondary rainbow, originate from a single base point and their colors are not inverted.

But nevertheless, for the scientific environment the classification of rainbows is even more detailed. A study released in 2015 by the French National Center for Meteorological Research, led by researcher Jean Ricard, establishes that there are twelve different types of rainbows and that this classification considers the number of visible colors, the projection of multiple arches and the alteration of the color of the sky between each arch. All these parameters make small differences between the types of rainbow that we describe above.

How is a rainbow formed?

The Rainbow is formed by the decomposition of a ray of light that passes through a drop of water suspended in the atmosphere. When a ray of light passes through a surface that divides two spaces of different densities (in this case, the air in the atmosphere and the drop of water), the ray refracts its path, that is, it slightly bends or changes the angle of trajectory . It is then reflected (bounced) off one of the faces inside the drop, and as it exits, the light beam is refracted again.

The Rainbow can appear anywhere there is moisture in the air, for example, near the splashes of a river or by the dew of the sea, and with the sun located in a specific position: less than 42º above the horizon. The observer must be positioned facing the drops of water and with the Sun behind him.

Why does the rainbow have seven colors?

Newton’s experiment consisted of a glass prism pierced by a ray of sunlight.

The ray of light that passes through the drop of water generates a decomposition of the white light in different wavelengths. These lengths are different from each other and give rise to the different colors of the rainbow. This concept of the “decomposition of light” was demonstrated by Isaac Newton in the seventeenth century, through an experiment with a glass prism that was pierced by a ray of sunlight. He found that white light consisted of colored bands that could be separated and visualized individually (as is the case with the rainbow).

Places with more rainbows

Among the places where rainbows are most visible, the following stand out:

  • Machu Pichu. Located in the Andes mountain range, in southern Peru, it is an ancient Inca town from the 15th century.
  • Victoria Falls. Located on the border between Zimbabwe and Zambia, in Africa.
  • Iguazu Falls. Located on the border between Argentina and Brazil.
  • Masai Mara Nature Reserve. Located in Kenya, Africa.
  • Tatras Mountains National Park. Located in the Tatra Mountains, Slovakia.
  • Jasper National Park. Located in the Rocky Mountains in Canada (declared a World Heritage Site by UNESCO in 1984).
  • Norfolk. Located in England, it is a city with fine sandy beaches.
  • Grinell Point Mountain. Located in Glacier National Park, Montana, United States.
  • Valle de las Flores National Park. Located in the state of Uttaranchal, in India (declared a World Heritage Site by UNESCO in 1998)
  • Mount Fuji. Located west of Tokyo, Japan. It is the highest peak on the island of Honshu, located west of Tokyo, Japan.