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Why the Sky Changes Colour

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The sky changes color throughout the day due to light scattering in the atmosphere. Blue light scatters more than other colors, which is why the sky appears blue when the sun is high. At sunrise and sunset, the sun's light passes through more atmosphere, scattering the shorter wavelengths and allowing the longer wavelengths like red and orange to dominate the sky. Additional factors like dust, pollution, clouds, and humidity can also influence sky color at different times of day.

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Why Does the Sky Change Colour as the Day Progresses? By Jonny T
Every colour change in sky is related to light and atmosphere Colour is what the human eye perceives when light is given off
1. Light
1. Light  Light waves are electromagnetic energies (electromagnetic spectrum!)  They have different waves and frequencies  Long wavelength = low frequency + energy  Travels at 299,792 km/sec (speed of light)
1. Light (cont’d)  Visible light looks white:  White is made up of different colours (monochromatic light)  Each colour is related to size of wavelength, frequency, and energy  Sun’s colours are arranged from short to long  Light with shorter wavelengths (ie: blue) are more easily absorbed in sky  Rayleigh scattering: process of absorbing light and scatter particles
2. Atmosphere
2. Atmosphere  Molecules present:  Carbon dioxide  Ozone  Hydrogen gas  Nitrogen gas  Oxygen gas  When light is shone, N2 gas and O2 gas will absorb the most energy… Let’s focus on these
2. Atmosphere (cont’d)  Called fluorescence  Electrons in N2 gas and O2 gas will be excited  Electrons become promoted to higher sublevel  They have a time-frame for which they can stay excited  Once reached, it may fall down energy sublevels or entire energy levels  Photon is released F L U O R E S C E N C E
2. Atmosphere – Fluorescence (cont’d)  Oxygen gas and nitrogen gas bright-line emission spectra  This is [half of the reason] why sky is blue!
2. Atmosphere (cont’d)  Atmosphere is thicker when it’s closer to the Earth (gravitational pull)  This is why horizon is another colour  More atmosphere = more molecules to scatter light  Thickness determined by weather patterns and human factors  Light travels straight until it hits an atmosphere particle  ie: when light hits water molecule, water acts as a
We Must First Understand… [The other half of] Why sky is blue.
Blue Sky  When Sun is high in the sky, it emits wavelengths at the shortest angle  What colour does the shortest angle allow for…?
Blue Sky (Part 2) Blue light is the shortest distance in atmosphere Atmospheric gases absorb blue and violet colours and cause them to scatter (more than any other colour) Rayleigh scattering Human eyes do not
Blue never goes away… we just cannot see it sometimes!
And finally… Sunrise and Sunset
 When Sun reaches Earth, there is a longer angle  What colours does the longest angle allow for…? As Sun gets higher in sky, these colours fade and blue light becomes more scattered  Blue sky returns Sunrise
 Reverse sunrise… but a bolder display  Dust/debris is being kicked around during the day  This filters light  Polluted cities have the most beautiful sunsets Sunset
How are the Details Determined?
Details Dust Pollution Smog Clouds Water vapour or humidity causes the sky to appear gray because it deflects light
The End!

More Related Content

Why the Sky Changes Colour

  • 1. Why Does the Sky Change Colour as the Day Progresses? By Jonny T
  • 2. Every colour change in sky is related to light and atmosphere Colour is what the human eye perceives when light is given off
  • 4. 1. Light  Light waves are electromagnetic energies (electromagnetic spectrum!)  They have different waves and frequencies  Long wavelength = low frequency + energy  Travels at 299,792 km/sec (speed of light)
  • 5. 1. Light (cont’d)  Visible light looks white:  White is made up of different colours (monochromatic light)  Each colour is related to size of wavelength, frequency, and energy  Sun’s colours are arranged from short to long  Light with shorter wavelengths (ie: blue) are more easily absorbed in sky  Rayleigh scattering: process of absorbing light and scatter particles
  • 7. 2. Atmosphere  Molecules present:  Carbon dioxide  Ozone  Hydrogen gas  Nitrogen gas  Oxygen gas  When light is shone, N2 gas and O2 gas will absorb the most energy… Let’s focus on these
  • 8. 2. Atmosphere (cont’d)  Called fluorescence  Electrons in N2 gas and O2 gas will be excited  Electrons become promoted to higher sublevel  They have a time-frame for which they can stay excited  Once reached, it may fall down energy sublevels or entire energy levels  Photon is released F L U O R E S C E N C E
  • 9. 2. Atmosphere – Fluorescence (cont’d)  Oxygen gas and nitrogen gas bright-line emission spectra  This is [half of the reason] why sky is blue!
  • 10. 2. Atmosphere (cont’d)  Atmosphere is thicker when it’s closer to the Earth (gravitational pull)  This is why horizon is another colour  More atmosphere = more molecules to scatter light  Thickness determined by weather patterns and human factors  Light travels straight until it hits an atmosphere particle  ie: when light hits water molecule, water acts as a
  • 11. We Must First Understand… [The other half of] Why sky is blue.
  • 12. Blue Sky  When Sun is high in the sky, it emits wavelengths at the shortest angle  What colour does the shortest angle allow for…?
  • 13. Blue Sky (Part 2) Blue light is the shortest distance in atmosphere Atmospheric gases absorb blue and violet colours and cause them to scatter (more than any other colour) Rayleigh scattering Human eyes do not
  • 14. Blue never goes away… we just cannot see it sometimes!
  • 16.  When Sun reaches Earth, there is a longer angle  What colours does the longest angle allow for…? As Sun gets higher in sky, these colours fade and blue light becomes more scattered  Blue sky returns Sunrise
  • 17.  Reverse sunrise… but a bolder display  Dust/debris is being kicked around during the day  This filters light  Polluted cities have the most beautiful sunsets Sunset
  • 18. How are the Details Determined?
  • 19. Details Dust Pollution Smog Clouds Water vapour or humidity causes the sky to appear gray because it deflects light

Editor's Notes

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