Which phenomenon is responsible for the blue colour of the sky? 

The correct answer is Scattering of light.

Key Points

• The blue colour of the sky is primarily due to the scattering of sunlight by the molecules in the atmosphere.
• This phenomenon is known as Rayleigh scattering, named after the British scientist Lord Rayleigh.
• Rayleigh scattering is more effective at shorter wavelengths, which is why the blue light (shorter wavelength) is scattered more than other colours.
• The scattered blue light reaches our eyes from all directions, making the sky appear blue during the day.

Additional Information

• Rayleigh Scattering
  • It occurs when the particles causing the scattering are smaller than the wavelength of light.
  • It is inversely proportional to the fourth power of the wavelength, meaning shorter wavelengths are scattered more.
  • This is why blue and violet light are scattered more than red light.
• Mie Scattering
  • It is another type of scattering that occurs with larger particles, such as water droplets and dust.
  • Mie scattering is less dependent on wavelength and is responsible for the white appearance of clouds.
• Atmospheric Refraction
  • It is the bending of light as it passes through the Earth's atmosphere.
  • This phenomenon is responsible for effects such as the apparent shift in the position of stars and the flattening of the sun near the horizon.
• Total Internal Reflection
  • It occurs when light travels through a medium and hits the boundary of another medium at an angle greater than the critical angle, causing it to be reflected entirely within the first medium.
  • This is the principle behind optical fibers and some natural phenomena like the sparkle of diamonds.
• Reflection
  • It is the process by which light bounces off a surface.
  • Reflection is responsible for the visibility of objects and is described by the laws of reflection.