Solve the mysteries of the rainbow – El Tiempo

The rainbow in the sky of the capital

In 1665, Isaac Newton first analyzed the technical details of the rainbow. Newton’s discoveries demonstrated the complexity and sophistication with which nature operates.

Nature surprises us with sensational phenomena. This is what happens to the one we all appreciate and for which the writer Mario Benedetti named one of his poems: Arcoíris. For millennia, contemplating majestic arches of color in Paradise, a true work of art of nature. It has been incorporated into the legends of ancient cultures, from the jewelry necklace of a great goddess to a bridge connecting two worlds, or even a messenger goddess between heaven and earth pointing to Iris in Greek mythology.

Today, in addition to the beauty we continue to admire in the rainbow, we can immerse ourselves in the beauty and perfection of the physical processes that make it possible. The first theory of its origin dates back to the Middle Ages (1301) in the optical studies of Theodoric von Freiberg, who used a spherical container filled with water to simulate a large peak. René Descartes gave a similar explanation to show the impact of light refraction on water droplets producing colors, although he only got azure and red.

It was the great sage Isaac Newton who presented his quest in 1667 to break the sunlight in a dark room and let a small burst of sunlight fall through a hole in the window. The light passed through a prism to finally form the bouquet of colors on the opposite wall. Newton identified seven colors: red, orange, yellow, green, azure, indigo and mauve. The sage did not choose this number arbitrarily; He did so motivated by its historical importance, mainly in Greek civilization, where the indication “Law of the Seven” was used.

In fact, in the rainbow there is a continuous sequence of different colors, and it is formed when the sun’s rays pass through suspended water droplets in the field, which act as prisms, c That’s why it appears on days when it rains or when the humidity is very high. .

Light rays enter and bounce off each vertex, building and refracting as they enter and exit. Each color bends in a different way, breaking down white light into its individual colors, known as the visible light spectrum. For example, the angle of refraction of yellow light (the middle one) is 138 degrees, which means that a meta-iris can only be seen when facing the sun. What we see are rays of different colors falling on our retina, coming from a large number of different droplets. It is as if each color moved from its cushion through the surface of a funnel and our lanterns were the top of this large funnel. Since the water drops are on the surface of the earth, we only see a meta and not a full circle of colors.

If the light reflects several times in the drops before leaving, several rainbows can form, although they are observed gradually fainter and with inverted colors.
The size and shape of the droplets change the intensity of the colors. Large ones form very intense and colorful meta irises, and when crushed by the shifting drag of elegance, they can make the cushion of the meta iris lighter than its top. Small droplets make them pale and opaque.

Romantic poet John Keats cursed Newton in 1820 for “stripping the rainbow of its intrigue”, but being able to understand these mysteries of nature is undoubtedly a triumph of knowledge and little we can tell. distinguished from other species.

PhD in astrophysics.

Original Spanish content

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