Friday Mar. 10, 2006
Graded quizzes were returned in class. Check the grading and the
point totals carefully.
The Expt. 4 materials will be available starting on Mon., Mar.
20. Reports will be due Friday Apr. 7.
Here are
links to the weather sites used in class:
Tucson office of the
National Weather Service
American
Meteorological Society (go to Watches, Warning, Advisories and
Forecasts)
NOAA
Graphical Forecast
The figure above is found on p. 107 in the photocopied
notes. The figure below was drawn in class.
Students in class will see the laser light only when chalk dust or
cloud droplets in the laser beam intercept and redirect some of the
light. Everyone that sees red light is looking back along a
different ray of light.
Particles with sizes equal to or greater than the wavelength of visible
light scatter all the colors equally. Air molecules are much
smaller than the wavelength of visible light and scatter shorter
wavelengths (violet, blue, green) more readily than longer
wavelengths (yellow, orange, red)
If you look at the sun while it is high in the sky you see the
unscattered light. It will be the white sunlight arriving at the
top of the atmosphere minus a very little bit of the shorter wavelength
purple, blue, and green light. This is illustrated below.
The unscattered light is still white with perhaps a slight yellowish
tint and is still intense.
As sunlight takes a longer and longer path through the atmosphere it
weakens (you knew that already). It also changes color becoming
yellow, orange, even red if the path is long enough and as the shorter
wavelengths are removed from the sunlight by scattering. This is
illustrated below
When you turn away from the sun and look at the sky you see blue
scattered light.
Now you are seeing the shorter wavlengths removed from the original
beam of sunlight and redirected.
The scattered light is much weaker and is composed mainly of shorter
wavelengths of light.
Cloud droplets, because of their size, scatter all the colors about
equally. That is why a clouds appears white.