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Rayleigh scattering

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Title: Rayleigh scattering


1
Rayleigh scattering
  • Light scattering in the atmosphere

2
Contents
  1. What is Rayleigh Scattering?
  2. Light scattering in the atmosphere
  3. Why is heaven blue?
  4. Why is rising and setting sun redish?
  5. Polarizsation
  6. What else?

3
1. What is Rayleigh scattering?
  • Named after John William Strutt,
  • 3rd Lord of Rayleigh, 1871
  • Definition
  • elastic scattering of electromagnetic radiation
    (light), by particles much smaller than the
    wavelength of the radiation

4
1. What is Rayleigh scattering?
  • The intensity I of light scattered by a single
    small particle from a beam of unpolarized light
    of wavelength ? and intensity I0 is given by
  • R - distance to particle,
  • ? - scattering angle,
  • n - refractive index of particle,
  • d - diameter of particle.

5
1. What is Rayleigh scattering?
  • Integrating over the sphere surrounding the
    particle gives the Rayleigh scattering cross
    section ss
  • The intensity of Rayleigh scattered light varies
    inversely with the fourth power of the wavelength
  • Violet light is scattered stronger than red light

6
2. Light scattering in the atmosphere
  • Sky is blue (or white if there are clouds)
  • (exept in Bremen, where it is gray most of the
    time)
  • reason
  • scattering of
  • sunlight by molecules
  • or microparticles in
  • the atmosphere

7
3. Why is heaven blue?
Source http//www.type.de/download/screens/bluesk
y_comp_04.jpg
8
3. Why is heaven blue?
  • Intensity distribution of sunlight (? max455nm)
  • Wavelength dependency of ss anti-proportional to
    ?4
  • Spectral distibution of our eyes sensitivity
    ?(?)

9
3. Why is heaven blue?
...it isnt!! It is violet!
  • physiological explanation
  • our eyes are less sensitive to violet light
    (400 nm) than to blue light.
  • Result the eye sees just the blue sky

http//en.wikipedia.org/wiki/Rayleigh_scattering
10
5. Why is rising and setting sun redish?
  • Sunrise on Rügen
  • from http//svenvogel.sv.funpic.de/Bilder/ruegen
    /Sonnenaufgang20Kap20Arkona09.JPG

11
5. Why is rising and setting sun redish?
  • light passes through a greater thickness of the
    atmosphere
  • multiple scatterings of blue light
  • but relatively little scattering of red light
  • red-hued sky in the direction towards the sun.

12
Polarization
  • Unpolarized Sunlight induces dipoles oscillating
    perpendicular to direction of the baem k
  • Intensity of scattering
  • ISI0 sin2 ? I0 cos2 a
  • Polarization dependent of visual angle
  • P(1-cos2 a)/(1cos2 a)

13
6. What else? Mie scattering
  • The general theory concerning scattering in the
    atmosphere is Mie theory (Gustav Adolf Ludwig
    Mie, 1868 1957)
  • arbitrary size parameter
  • in case of x ltlt 1 Mie theory reduces to
  • Rayleigh approximation

14
6. What else? Mie scattering
15
List of literature
  • Demtröder, Experimentalphysik 2, 2. Auflage,
    Springer
  • Meschede, Gerthsen Physik, 21. Auflage, Springer
  • Tipler, Physik, 1. Auflage, Spektrum Akademischer
    Verlag

16
End
  • Thank you for your attention!
  • Any questions?
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