How Do Rainbows Appear? Here’s the theory

How Do Rainbows Appear? – Pelangi is very famous for its beauty that can make us continue to see it. Even hope that the rainbow does not disappear soon. The beauty of the rainbow comes from its distinctive colors which are known as “mejikuhibiniu”.

Usually, a rainbow will appear when it rains or after the rain is over. The appearance of the rainbow is generally in the form of a semicircle. Rainbows do not just appear there is a process of occurrence and the factors that cause rainbows to appear.

It will be lacking if we only enjoy the beauty of the rainbow, but don’t know the process of its occurrence and the factors that cause it. To find out about these two things, let’s look at the reviews as follows.

Before discussing how the process of rainbows occurs, we should first identify what a rainbow is.

Meaning of Rainbow

The definition according to some experts is similar but not the same. The following is the meaning of the rainbow, which is expressed by several experts.

1. Nancy Thompson

Isaac Newton said that a rainbow is a spectrum resulting from bending or deflection of light entering a prism.

2. Donald Ahrens

An explanation of the rainbow was written by Donald Ahrens in his book Meteorology Today . In his book, Donald Ahrens says that the rainbow is never parallel to the location of the sun. Based on this opinion, it can be said that the location of the rainbow will always be opposite the sun.

3.Lord Rayleigh

According to Lord Rayleigh, the rainbow is a process of refraction of light that gives rise to a light effect with various colors. In this process, water vapor particles surrounding the light distort the light itself to create a beautiful blend of colors to behold.

Whereas in the Big Indonesian Dictionary (KBBI) a rainbow is a curved spectrum in the sky, visible due to the refraction of sunlight by raindrops or dew.

Inventor of the Theory of the Rainbow Appearance

Al-Qarafi is a scientist who was born in 1228 AD and was born in Bahnasa, Egypt. He is also known as someone who is an expert on kalam as well as one of the Islamic jurists who belongs to the Maliki school of law.

The process of the occurrence of a rainbow is written in Al-Qarafi’s scientific work. This scientific work is in the form of a book with the name Al-istibar fi ma Tudrikuhul Al-Abshar. The meaning of the name of the book is “About What the Eyes Catch”.

In his scientific work, Al-Qarafi explains that the appearance of a rainbow in the sky is caused by the reflection of sunlight on the smoke or vapor in the sky. The explanation explained by Al-Qarafi can be said to be the same as that of a philosopher, namely Ibn Sina.

According to Al-Qarafi, the rainbow has two colors, namely the color of smoke and the sun and the colors that are composed of these two elements. Not only about the colors of the rainbow, he also explained that the color of an object will not be the same when it is reflected in the mirror. The color of the object and the mirror will bring out the color that comes from the reflection of the mirror.

Many scientists make Al-Qarafi’s theory a basis or guideline for discussing rainbows.

Factors Causing Rainbows

1. Light

Light has various properties that can help the rainbow process. Because of this, light is a factor that causes rainbows.

a. The properties of light

1)  Straight vines

The first characteristic of light is that it propagates straight. Light that propagates straight can be seen when the light passes through an intermediate medium.

One example is when the flashlight is turned on and pointed forward, the flashlight will point straight in the desired direction.

2)  Can be bounced

The next property of light is that light can be reflected. Reflected light can be said to be the process of returning light from objects or objects that are exposed to light. Reflected light has two properties, namely regular reflection and diffuse reflection.

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One example of the nature of this light is a mirror that is directed at the sun will cause the reflection of light coming from the sun’s rays.

3) Can be deflected / refracted

The next property of light is that light can be bent or refracted. Light refraction (refraction) is the deflection of the direction of propagation of light when it enters another medium with a different optical density.

One example of light can be bent or refracted, namely when we dip a pencil in water in a glass, the pencil will look like it is broken or bent.

A pencil that looks broken when placed in water is caused by the refraction of light from air as a tenuous medium to water, which is a denser medium.

4)  Light can be deciphered

The next property of light is light can be described. Basically, the decomposition of light has occurred naturally. We can see the decomposition of light in the appearance of a rainbow.

When a rainbow appears, you will see various colors even though the basic color of the rainbow is white. This white color is obtained from sunlight. This white light will decompose after it is refracted by rainwater, giving rise to various colors.

5)  Light can experience diffraction

The next property of light is that light can experience diffraction or bending. Bending in light occurs when light has to pass through a narrow area. After the light has experienced bending, the light will be fragmented so that it can bring out new light properties.

Diffraction itself is divided into two, namely single slit diffraction and lattice diffraction. The parable of light diffraction can be done by placing a ball or other object on the surface of the water. Then the surface of the water will produce vibrations (split light). Meanwhile, the ball can be said to be a new source of light

6) Light can penetrate transparent objects

The last characteristic of light is that light can penetrate clear. On clear objects the light will be translucent and able to transmit light. However, on dark objects, light can only form a shadow because it cannot penetrate dark objects.

Light can penetrate clear objects by burning wood, paper, leaves, etc. only with a magnifying glass. The fire to burn the goods comes from the sun’s rays which are directed with glass (clear).

Those are the properties of light. All of these properties have their respective functions. Therefore, the use of light will be maximized if it uses light according to its function.

Light itself is an energy in the form of waves that can be seen by our eyes and has a wavelength of about 380-750 nm.

Meanwhile, in the Big Indonesian Dictionary (KBBI) light means light or light (from something that shines such as the sun, moon, lamp) that allows the eye to catch the shadows of objects around it.

In some studies, light has a speed of about 186,282 miles per second in a vacuum. In fact, no one has yet been able to exceed the speed of light. If you could travel at the speed of light, it would be like 7.5 times around the earth.

Light for everyone is a necessary component, just like the lamp and the sun. When the lights go out, we usually complain because we can’t get any light. Meanwhile, if there is no sun during the day we will be confused about how to dry clothes.

The Nature of Light That Causes Rainbows

After knowing the properties of light, it can be said that almost all the properties of light can cause a rainbow to occur, such as the nature of light can be described, with the nature of this light, the colors in a rainbow can appear.

White sunlight actually consists of several colors. The ability of light to separate its colors is what causes the rainbow process to occur. White is a collection of various colors. So also white light, white light is polychromatic alias can be separated into other colors

The decomposition of white into several other colors is called dispersion. Dispersion arises because there is a difference in the index of refraction between each light so that when it passes through a light medium, several colors similar to a rainbow come out.

In addition, the nature of light can be deflected can be regarded as a factor in the appearance of a rainbow. In the process of the occurrence of a rainbow, the nature of this light appears when light (sunlight) passes through water droplets originating from the earth’s atmosphere.

2. Water

Another component that causes a rainbow is water. The water in question is not just rainwater, but water that can come from anywhere. In other words, as long as there is water and light, rainbows can form.

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The size of the raindrops that light passes through affects the complete color of the sun. The size of small raindrops is only about 0.01 millimeters while for large ones it is 2 millimeters. The larger the size of the water droplets that are passed, the more complete the rainbow colors that appear. Meanwhile, if the grain is small, the colors that appear will overlap and even fade. So, if we see a beautiful rainbow, it means that the water droplets passing through are large.

The rainbow process

1. Refraction of sunlight

The formation of a rainbow is caused by the process of refraction of light (sunlight) which is deflected so that it moves from one medium to another with the help of water droplets originating from the earth’s atmosphere.

2. Sunlight passes through water droplets

After sunlight passes through the water droplets, what will happen is that the light (sunlight) will be bent or bent so that the colors of the light will separate from each other and give rise to new colors.

3. Light deflection

Every color that comes out of the deflection of light usually has a variety of colors. These colors are what we know today as the rainbow.

4. The appearance of rainbow colors

If we have ever heard the term “mejikuhibiniu” it means that indirectly we have the order of the colors of the rainbow from end to end. In other words, red is the last color to be deflected, while purple is the first color to be deflected.

The rainbow is known to be very beautiful with its distinctive colors because these colors can make our eyes want to keep seeing it.

Behind the beautiful colors of the rainbow there is a very complicated process. This complicated process causes rainbows to be rarely seen by us. That’s why when a rainbow appears before us, we will feel very happy because we rarely see a rainbow appear.

There is a fact that says that the appearance of a rainbow at or shortly after it falls is more likely to occur. Therefore, when we were children, we would always wait for a rainbow to appear when it started to rain.

Rainbow Types 

1. Primary Rainbow

The rainbow that we often see is the primary rainbow. The formation of the primary rainbow is due to the process of refraction and reflection of light that enters the raindrops.

The colors that will appear after the refraction process are purple, blue, green, yellow, orange, and red. The red color of the rainbow forms an angle with sunlight, that angle is approximately 42 degrees.

2.Secondary Bow 

A secondary bow type rainbow is a rainbow in the form of a secondary arc. This type of rainbow is included in a rare type of rainbow. Why can it be said to be a rare type of rainbow? This is because the appearance of the secondary bow rainbow can only be seen after the primary rainbow appears

Thus, this secondary bow rainbow is included in the secondary rainbow. The colors in the secondary rainbow appear dimmer compared to the primary rainbow.

3. Waterfall Rainbows

Waterfall rainbows or what we usually know as rainbow waterfalls. Waterfall rainbows are rainbows that only appear or can be seen above a waterfall. In general, the appearance of waterfall rainbows occurs because of the fog on the waterfall that enters or mixes with the airflow around it. Continuously.

4. Lunar Rainbows

Did you know that there is a type of rainbow that is caused by the light coming from the moon? Rainbows caused by light from the moon are known as lunar rainbows .

Basically, the process of appearing lunar rainbows is almost the same as that of primary rainbows. The thing that distinguishes the lunar rainbow is the light source.

Rainbow types of lunar rainbow will look brighter when the full moon appears. Why is it only during a full moon that the lunar rainbow appears brighter? Because the light on the full moon is brighter than other months.

5. Sundogs

A rainbow of sundogs can be said to be a rainbow that only appears in winter and when the weather is sunny. The appearance of rainbow sundogs generally occurs when sunlight shines through ice crystals that are very high in the atmosphere.


All the beautiful colors in the rainbow are very beautiful. All that beauty cannot be separated from the factors that cause rainbows to appear. Water and light are the two main factors that cause a rainbow.

Author: Irma Tri Handayani & Restu Nasik Kamaluddin

Book Title: Rainbow and Rain: Between Memories and Wishes

Book Title: Rain and Rainbow

Book Title: A Million Rainbow Colors

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