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# Blue sky

This is the outline for a future lesson on Rayleigh Scattering: Why the sky is blue

– Rayleigh scattering occurs when light is scattered off many very small particles.
– Mie scattering occurs when light is scattered off of many larger particles.

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Question: Particles in the air cause shorter wavelengths (blue-ish0 to scatter more than the longer wavelengths (reddish.) This causes us to see the sky as being blue. So why does the sunrise (or sunset) and sun look red/orange?

Answer: “When you look at the sky and see blue you’re seeing blue light being scattered towards your eye.”

“When you look at the sun and it looks red or orange that’s because the blue light is being scattered away from your eye – leaving the remaining light to enter your eye.”

“The blue light is being scattered in all directions by Raleigh scattering. The colors you see depend on what direction you’re looking.”

## External resources

http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html

https://www.itp.uni-hannover.de/~zawischa/ITP/scattering.html

http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html

http://www.thephysicsmill.com/2014/03/23/sky-blue-lord-rayleigh-sir-raman-scattering/

Brownian motion app  galileoandeinstein Brownian motion app

Lesson EarthRef.org Digital Archive ematm.lesson3.scattering.pptx

EM in the Atmosphere: Reflection, Absorption, and Scattering Lesson Plan

Powerpoint for the lesson plan

## Learning standards

### SAT subject test in Physics: Waves and optics

• General wave properties, such as wave speed, frequency, wavelength, superposition, standing wave diffraction, and Doppler effect
• Reflection and refraction, such as Snell’s law and changes in wavelength and speed
• Ray optics, such as image formation using pinholes, mirrors, and lenses
• Physical optics, such as single-slit diffraction, double-slit interference, polarization, and color

### AP Learning Objectives

IV.A.2.b: Students should understand the inverse-square law, so they can calculate the intensity of waves at a given distance from a source of specified power and compare the intensities at different distances from the source.

IV.B.2.b: Know the names associated with electromagnetic radiation and be able to arrange in order of increasing wavelength the following: visible light of various colors, ultraviolet light, infrared light, radio waves, x-rays, and gamma rays.

L.2: Observe and measure real phenomena: Students should be able to make relevant observations, and be able to take measurements with a variety of instruments (cannot be assessed via paper-and-pencil examinations).

L.3: Analyze data: Students should understand how to analyze data, so they can:
– a) Display data in graphical or tabular form.
– b) Fit lines and curves to data points in graphs.

L.5: Communicate results: Students should understand how to summarize and communicate results, so they can:
– a) Draw inferences and conclusions from experimental data.
– b) Suggest ways to improve experiment.
– c) Propose questions for further study