Which gas is responsible for the blue color of the Earth’s atmosphere?

The correct answer is Nitrogen (N2) and Oxygen.

Key Points

• The blue color of the Earth's atmosphere is primarily caused by the scattering of sunlight by molecules of Nitrogen (N2) and Oxygen.
• This phenomenon is explained by Rayleigh scattering, where shorter wavelengths of light (blue) are scattered more than longer wavelengths (red).
• Approximately 78% of the Earth's atmosphere consists of Nitrogen and 21% of Oxygen, making these gases dominant contributors to atmospheric scattering.
• The scattered blue light is what gives the sky its characteristic blue appearance during daylight hours.
• The intensity of the scattering is inversely proportional to the fourth power of the wavelength, meaning shorter wavelengths like blue are scattered more effectively.

Additional Information

• Rayleigh Scattering:
  • It is a type of scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation.
  • Rayleigh scattering is responsible for the blue color of the sky and the reddish-orange hues during sunrise and sunset.
  • The scattering is most effective for shorter wavelengths like violet and blue.
• Composition of Earth's Atmosphere:
  • The Earth's atmosphere is composed of 78% Nitrogen, 21% Oxygen, and trace amounts of other gases like Argon, Carbon dioxide, and water vapor.
  • Nitrogen and Oxygen play a significant role in scattering sunlight, creating the sky's blue color.
• Sunset and Sunrise Colors:
  • The reddish hues seen during sunset and sunrise are due to the scattering of longer wavelengths (red and orange) when the sun is at a lower angle.
  • At these times, sunlight passes through a larger thickness of the atmosphere, scattering shorter wavelengths like blue away and leaving the longer wavelengths visible.
• Why Does Space Appear Black?
  • In the absence of an atmosphere, like in outer space, there are no particles to scatter sunlight, causing space to appear black.