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Why the Sky is Blue?

📑 10 slides 👁 49 views 📅 1/21/2026
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Introduction

The sky appears blue due to a phenomenon called Rayleigh scattering.

Introduction
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Sunlight Composition

  • Sunlight is made up of all colors of the visible spectrum.
  • When combined, these colors appear as white light to our eyes.
  • Each color has a different wavelength, with blue being shorter.
Sunlight Composition
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Rayleigh Scattering

  • Named after Lord Rayleigh, who first explained it in the 19th century.
  • Shorter wavelengths (blue/violet) scatter more than longer ones (red).
  • This scattering is inversely proportional to the 4th power of wavelength.
Rayleigh Scattering
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Atmospheric Particles

  • Nitrogen and oxygen molecules in the atmosphere cause the scattering.
  • These particles are much smaller than the wavelength of visible light.
  • The density of these particles affects how much light is scattered.
Atmospheric Particles
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Why Not Violet?

  • Violet light is scattered even more than blue light.
  • Our eyes are less sensitive to violet and more sensitive to blue.
  • Sunlight contains less violet light compared to blue light.
Why Not Violet?
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Sky Color Variations

  • At sunrise/sunset, the sky appears red/orange due to longer light path.
  • More atmosphere means more scattering of blue light, leaving red hues.
  • Clouds appear white because they scatter all colors equally.
Sky Color Variations
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Altitude Effects

  • At higher altitudes, the sky appears darker blue (less atmosphere).
  • Astronauts see black sky as there's no atmosphere to scatter light.
  • Mountaintop skies have more intense blue color than sea level.
Altitude Effects
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Other Planets' Skies

  • Mars has blue sunsets but reddish daytime sky due to dust.
  • Venus' thick atmosphere makes its sky orange all the time.
  • Titan's orange sky comes from organic compounds in its atmosphere.
Other Planets' Skies
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Historical Understanding

  • Leonardo da Vinci was among the first to study sky color scientifically.
  • John Tyndall demonstrated light scattering in the 1860s.
  • Rayleigh provided the complete mathematical explanation in 1871.
Historical Understanding
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Conclusion

  • The blue sky results from Rayleigh scattering of sunlight.
  • Blue light scatters more due to its short wavelength.
  • This phenomenon also explains colorful sunrises and sunsets.
Conclusion
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