1. Chapter 15: Light, Color and Atmospheric Optics
White and colors
White clouds and scattered light
Blue skies and hazy days
Red suns and blue moons
Twinkling, twilight, and the green flash
The mirage: seeing is not believing
Halos, sundogs, and sun pillars
Rainbows
Coronas and cloud iridescence

2. White and Colors Review:
Nearly half of radiation from sun is visible light (what wavelengths are longest?)
Four possible fates of light as it enters atmosphere (absorbed, reflected, scattered, transmitted)
So what wavelengths is all white light? Black light?
We see using rods and cones

3. White Clouds and Scattered Light
Reflection – occurs when sunlight bounces off a surface at same angle
Scattering – occurs when sunlight is deflected in all directions
Why is the bottom of thunderstorms dark?

4. Blue Skies and Hazy Days
Selective scattering – ability of molecules to scatter one wavelength better than others
The larger the particle, the more they scatter all wavelengths. Haze is white because of this
Crepuscular rays – scattering of sunlight by dust and haze to produce white bands of light

5. Red Suns and Blue Moons
Sun can appear red because it travels through more atmosphere near sunset than at midday
Blue moon and suns can happen if the particle is the same size as visible light (scattered red more)
Volcanoes can cause red suns for many days

6. Figure 15.8: Because of the selective scattering of radiant energy by a thick section of atmosphere, the sun at sunrise and sunset appears either yellow, orange, or red. The more particles in the atmosphere, the more scattering of sunlight, and the redder the sun appears.
Fig. 15-8, p. 420

7. Figure 15. 9: Red sunset near the coast of Iceland
Figure 15.9: Red sunset near the coast of Iceland. The reflection of sunlight off the slightly rough water is producing a glitter path.
Fig. 15-9, p. 420

8. The Mirage: Seeing Is Not Believing
Refraction – bending of light due to density changes
Light that travels from less to more dense loses speed, and vice versa
Lights twinkle due to refraction
Twilight occurs due to refraction

9. The Mirage: Seeing Is Not Believing
Mirage – an image that appears displaced from its true position
Caused by light moving through different air densities
Inferior mirage – images that appear lower and inverted from original
Superior mirage – images that appear higher than original

10. Inferior Mirage Warm surface, decreasing temperatures aloft
The proper conditions for an inferior mirage are commonly found over a hot road surface during summer, or over an unfrozen lake on a very cold day.

11. Figure 15.16: Inferior mirage over hot desert sand.
Stepped Art
Fig , p. 424

12. Superior Mirage Cold surface, warmer temperature aloft
The proper conditions for a superior mirage are commonly found over water and over snow-covered surfaces.

13. Figure 15. 17: The formation of a superior mirage
Figure 15.17: The formation of a superior mirage. When cold air lies close to the surface with warm air aloft, light from distant mountains is refracted toward the normal as it enters the cold air. This causes an observer on the ground to see mountains higher and closer than they really are.
Stepped Art
Fig , p. 425

14. Fata Morgana Complex vertical temperature profile
According to legend, King Arthur’s half-sister, Fata Morgana in Italian, was a fairy enchantress trained by Merlin the Magician. She lived in a crystal palace beneath the water and could build fantastic castles from thin air.

15. Halos Halo – Ring of light encircling sun or moon
Ice crystals refract light to create halo
Dispersion – breaking up of light into different wavelengths (prism)

16. Sundogs Created by hexagonal ice crystals oriented horizontally
Ice crystals act like a prism
Sundogs are commonly seen when cirrostratus clouds are in the sky.

17. Sun Pillars Caused by reflection of light off ice crystals
Sun pillars can be seen shortly after sunrise or shortly before sunset on very cold days.

18. Sun Pillars

19. Rainbows Water droplet phenomenon
When sunlight enters rain drop, it refracts and disperses
Red refracts less than violet
This light is reflected off backside of raindrop at critical angle
Each wavelength is reflected at different angle to our eyes (dispersed)
It takes many different raindrops to produced a rainbow (each raindrop gives a different wavelength)
Must face the falling rain with sun at your back
The primary rainbow, the brightest of the rainbows

20. Figure 15.26: When you observe a rainbow, the sun is always to your back. In middle latitudes, a rainbow in the evening indicates that clearing weather is ahead.
Fig , p. 429

21. Figure 15. 28: The formation of a primary rainbow
Figure 15.28: The formation of a primary rainbow. The observer sees red light from the upper drop and violet light from the lower drop.
Fig , p. 430

22. The Secondary Rainbow Two internal reflections (secondary rainbow)
A tertiary rainbow also exists, but it is too faint to be seen with the human eye.

23. Coronas and Cloud Iridescence
Diffraction – bending of light around objects
Corona – Bright ring of light around the moon or sun
Blue appears on inside of ring, red on outside

24. The Corona Need a cloud that has droplets of similar size
New clouds are the best corona producers

25. Cloud Iridescence Iridescence - bright areas produced by diffraction
Associated with thin clouds within 20 degrees of sun

26. The Glory Sun must be to your back, cloud in front of you
It is very common to see a glory from the window of an airplane. Make sure you are sitting on the side opposite the sun.