Formation of Rainbow – It is one of the most incredible masterpieces of Mother Nature. It is hard not to admire the beauty of this meteorological process when it occurs in several shapes and shades across the sky. The formation of a rainbow can be explained by the process of dispersion of light. In fact, a rainbow is the most accurate and excellent demonstration of this process in nature.
Formation of rainbow and its phenomenon
A rainbow is a multicolored arc that appears across the sky. It is formed by the phenomenon of light striking the water droplets suspended in the air. More precisely, it is a meteorological phenomenon that is caused by the reflection, refraction, and dispersion of light in water droplets. This results in a spectrum of light appearing in the sky.
Rainbows caused by sunlight always appear in that part of the sky that is directly opposite the Sun. The Sun is usually behind an observer. And the center of the rainbow is the anti-solar point (the point right opposite to the Sun). Rainbows are, however, optical illusions and do not appear on a particular spot in the sky. The appearance of a rainbow is dependent on the position of an observer and the direction in which the Sun is shining.
The sequence of formation of a rainbow
The vast collection of water droplets in the air after rain or a light mist, act as tiny prisms or refractors of light in the air. The water droplets act as prisms because they are optically denser than the surrounding air. Therefore, when light from the Sun travels through water droplets, it experiences a change in the densities of the two mediums. This affects the speed of light, decreasing it and causing it to bend inside the droplet towards normal. And gain back the speed and again bend away from the normal while exiting the droplet. This process causes a rather significant deviation in the original path of the light.
Now, there can innumerably paths through which the white light can enter the water drop and deviate from its path. One such significant path is when the white light follows refraction during entering. Then internal reflection and then again refraction during the exit. A ray of light from the sun enters a water drop and suffers refraction. The white light splits into different wavelengths due to the change in medium and thus, the speed. It also bends towards the normal inside the droplet. After refraction, the light dispersed by the prismatic action of the drop travels in the drop and hits the surface of the drop at an angle that causes the occurrence of total internal reflection. Now, after reflection, the light travels and hits the surface. Here, it experiences refraction, and this time bends away from normal.
In doing so, refraction forces the lights of different wavelengths apart. And disperse them into the atmosphere as different colors of lights. This gives the rainbow its multi-colored appearance in which there is a sequence of seven colors.
This entire process describes the sequence of different processes that take place for the formation of a rainbow. The ray of light from the sun first undergoes reflection, refraction, dispersion, total internal reflection, second refraction, and finally, dispersion of the refracted light into the atmosphere.
The sequence of color formation in a rainbow
The outcome of all these processes occurring in the atmosphere is the appearance of a beautiful, mesmerizing spectrum of several colors in the sky. But the important question that arises here is why are there so many colors in a rainbow and how do they appear? Well, it has already been established earlier that the refraction causes the white light to disperse into its component colors in the water droplet. Each of these colors has a different wavelength and travels at a different speed in different mediums. After double refraction, these lights of seven colors are pushed further apart and dispersed into the atmosphere.
Thus, a rainbow of seven colors is formed in the sky. These seven colors observed in a rainbow are in the sequence of VIBGYOR. This stands for Violet, Indigo, Blue, Green, Yellow, Orange, and Red. As a matter of fact, all these colors are not separately and distinguishingly visible to an observer. The human eye is only able to detect a maximum of five colors in a rainbow with Red being the first and the most detectable color in the rainbow.
The conditions for the rainbow formation
Rainbows, though a pretty sight, are quite a rare occurrence. That is because several conditions need to be fulfilled for the formation of a rainbow. Only when all such conditions are met, is a rainbow visible. The position of the sun needs to be behind the viewer. The sun needs to be low enough in the sky. It should be at an angle of less than 42° above the horizon. The lower the sun in the sky the more of an arc of a rainbow the viewer will see Rain, fog, mist, or some other source of water droplets must be present in front of the viewer.
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