Blue colour of the sky is due to: (a) absorption of light by dust particles (b) reflection of light by dust particles (c) scattering of light by dust particles (d) presence of clouds

The term 'Rayleigh scattering' refers to the physical process that explains why the sky is predominantly blue during daylight hours. Named after the British physicist Lord Rayleigh, this type of scattering occurs when sunlight interacts with the tiny molecules of air in the Earth's atmosphere. Light is made up of different colors, which correspond to different wavelengths.

Blue light has a shorter wavelength than other visible colors and is more easily scattered in all directions by the small molecules and particles in the atmosphere. This scattering sends blue light waves to our eyes from all angles, giving the impression of a blue sky overhead. Clear days offer the best examples of this phenomenon because there are fewer larger particles in the air to interfere with this scattering process.

While longer wavelengths pass through the atmosphere more directly, shorter wavelengths, like blue and violet, are scattered much more. Interestingly, our eyes are more sensitive to blue light, which is why we perceive the sky as blue instead of violet, the color that is actually scattered even more than blue.

The color of the sky is a spectacular display of light interacting with Earth's atmosphere. Our perception of the sky's color at any given time depends largely on the scattering of light. As previously mentioned, Rayleigh scattering is the primary reason we see a blue sky. However, the sky's color can change under different conditions.

At sunrise and sunset, the sky can take on vibrant hues of orange, pink, and red. This is because the light from the sun has to pass through a greater thickness of the Earth's atmosphere due to its position relative to the horizon. Longer wavelength colors like red, orange, and yellow are less scattered, and thus, more of those colors reach our eyes.

Additionally, the presence of larger particles like water droplets or pollution can also scatter light differently, leading to various sky colors. For example, after a heavy storm, when the air is clear of dust and other particles, the sky can appear a deeper blue.

Understanding the fundamental properties of light is essential to grasp why the sky appears blue. Light travels as both a particle and a wave, a concept known as wave-particle duality. Each color of light has a specific wavelength, with violet having the shortest wavelength visible to us and red having the longest.

The speed of light is about 299,792 kilometers per second in a vacuum, but when it passes through various mediums like the Earth's atmosphere, it can slow down and change direction—a process called refraction. The varying colors of light refract differently, which is why we can see the separation of colors in a rainbow when light passes through water droplets.

Moreover, light intensity and coherency are properties that can affect how light behaves when it encounters obstacles or openings. Understanding these properties helps in deducing various atmospheric phenomena, including the scattering of light, which is essential for explaining natural occurrences like the blue sky.