How is a Rainbow formed?

The magical dance of colors that appears in the sky after the rain is what we know as the rainbow, an optical and meteorological phenomenon that has captured the attention of humanity since ancient times. Its beauty makes it a natural spectacle that arouses fascination in people of all ages.

This phenomenon occurs when sunlight is refracted, reflected and dispersed inside the water droplets that make up rain, which gives rise to the separation of its colors in the visible spectrum and finally designs the majestic rainbow. that we admire.

For this spectacle of colors to form, the observer must have his back to the sun and the rain in front of him. Its position in the sky will depend on the angle of incidence of sunlight on the water droplets, so observing it will always be a unique and personalized event.

Contemplating a rainbow is an experience that connects us with nature, invites us to appreciate the magic of the world, the beauty that surrounds us and to enjoy the small details of our existence. A reminder that nature always has something new to offer us, if we just pay attention.

Basic principles of optics related to the rainbow

Optical principles essential to understanding rainbow formation include:

• Refraction: Light undergoes a change of direction when passing through drops of water. Each color is refracted at a different angle due to its wavelength.
• internal reflection: The light reflected from the back of the drop helps to increase the intensity of the rainbow colors.
• Dispersion: When refracted, light disperses into its constituent colors. This occurs because each color travels at different speeds within the water drop.
• Diffraction: It is a minor effect that occurs when light bends around the edges of water droplets, slightly blurring the colors of the rainbow.

These phenomena result in a spectrum of light that we observe as an arc composed of several colors, always in the same order due to the consistency of these principles of optics.

Decomposition of white light and colors

White light, like that of the Sun, is composed of a spectrum of colors that are often not perceived until decay occurs. This phenomenon occurs when white light passes through water droplets in the atmosphere. Each color has a different angle of refraction due to the different wavelength it has:

• Red light, with the longer wavelength, bends less.
• Other colors such as orange, yellow, green, blue, indigo and violet have progressively shorter wavelengths and refract more.

This separation of colors originates the rainbow visible in the sky. Individually, each drop of water disperses the entire range of colors, but only one color from each drop reaches the observer’s eye, thus making up the complete spectrum.

Meteorological factors in the formation of this phenomenon

For a rainbow to form, several meteorological factors must occur simultaneously:

• Presence of humidity: Water must exist in the atmosphere, generally in the form of raindrops, although it can also form with fine fog, dew, and occasionally volcanic ash and aerosols.
• Sunshine: It is necessary for the sun to shine while it rains. This usually occurs when the rain is stopping and the sun is beginning to rise or in storms where sunlight can filter through the clouds.
• Specific angle: The observer must be between sunlight and rain, with the sun behind him. The ideal angle for the appearance of the rainbow is 42 degrees with respect to the direction of the incident light.
• Reflection, refraction and dispersion: When light passes through water droplets, a first refraction occurs, then an internal reflection, and upon leaving, a second refraction that disperses the light into its spectrum of colors.

Reflection, refraction and dispersion: key processes

The formation of a rainbow is an optical phenomenon that involves three crucial physical processes: reflection, refraction and dispersion.

• Reflection: When sunlight hits raindrops, some of it reflects off the inner surface of the drop and then leaves it.
• Refraction: As light enters and leaves the drop, it refracts, or changes direction, due to the difference in the speed of light between air and water.
• Dispersion: Due to refraction, the different colors that make up white sunlight are dispersed at different angles depending on their wavelength, separating to form a spectrum of colors.

Variations of the common rainbow: double and circular

Rainbows do not always present themselves in the same way. Sometimes we can witness even more surprising phenomena, such as double rainbows and circular rainbows.

Double rainbows:

These peculiar rainbows are formed when sunlight is reflected twice inside raindrops. This double reflection creates a second arc that appears above the primary arc, with the colors inverted. A spectacle that is undoubtedly worth seeing.

Circular rainbows:

Although less common than double rainbows, circular rainbows can be observed from high altitudes, such as on airplanes or mountains. In this case, sunlight is dispersed evenly around the observer, causing a colorful ring to surround their shadow. A phenomenon that reminds us of the majesty of nature and the complexity of its physical processes.

Factors that influence your training:

The appearance of these double and circular rainbows depends on various factors, such as the position of the sun in the sky, the shape and size of the raindrops, and the height at which the observer is located. Each one of them contributes to creating a unique and unrepeatable show.

Contemplating these rare rainbows invites us to look up and discover the beauty hidden in the details. A reminder that nature always has something new to offer us, if we just pay attention.

The influence of viewing angle and sun position

The formation of a rainbow is directly linked to the position of the observer with respect to the sun and the water droplets responsible for its creation. For a rainbow to form, the sun must be behind the observer, and sunlight must enter the water droplets at a specific angle. This phenomenon occurs because light is refracted as it enters and leaves the drop, disperses within it and is reflected from its back. Refraction and internal reflection depend on the angle at which the light hits the drop. An optimal angle is typically found when the sun is at a low degree, generally less than 42 degrees above the horizon. This means that rainbows are usually observed during the mornings or afternoons when the sun is low enough. The height and angle of the sun affect the shape and intensity of the rainbow’s colors.

Cultural importance and symbology

The rainbow has rich symbology across diverse cultures. In Greek mythology, it represented a message from the gods. In the Bible, it is a symbol of the alliance between God and humanity after the flood. Many indigenous cultures consider it a bridge between heaven and earth.

In contemporary times, the rainbow is an emblem of peace and hope. Additionally, it has been adopted by the LGBTQ+ movement as a sign of diversity and pride. This meteorological phenomenon transcends its scientific explanation to become a powerful cultural icon that evokes unity and respect for diversity in society.

Photographing the Rainbow: Techniques and Tips

To capture the ephemeral essence of the rainbow with a camera, several factors must be considered:

• Lightning: A rainbow is best presented with a dark background and sky lit from behind. Find the right contrast.
• Time of the day: The art of photographing rainbows is enhanced at dawn or dusk, when the sun is low.
• Camera settings:
  • Manual mode: Adjust shutter speed, aperture and ISO to control exposure.
  • polarizing filter: Use to intensify colors and reduce reflections.
• Composition: Include elements in the foreground to give depth to the image, highlighting the magnificence of the rainbow.
• Application of the rule of thirds: Position the rainbow on one of the strong points to create a balanced and pleasing composition.

These guidelines will help immortalize the fleeting beauty of this natural phenomenon.

Conclusion: The rainbow as a union of science and beauty

The rainbow emerges as a visual spectacle where science and beauty harmoniously intertwine. Its colors display a dance of light reflected, refracted and dispersed by water droplets, illustrating fundamental optical laws in a natural exhibition that captivates observers of all ages. Understanding its formation intensifies aesthetic appreciation, transforming the observation of this phenomenon into an enriching experience that fuses knowledge and admiration for nature.

Ambientum Editorial