Chapter 15:
Atmospheric
Optics
Fig. 15-CO, p. 414
White Clouds and Scattered
Light
• reflection
• scattering
• Thunderstorms appear dark because the clouds
(cumulonimbus) are about 10 km deep, scattering
most of the light.
Cloud droplets scatter all wavelengths of visible white light about equally. The different
colors represent different wavelengths of visible light.
Fig. 15-1, p. 417
Since tiny cloud droplets scatter visible light in all directions, light from many billions of
droplets turns a cloud white.
Fig. 15-2, p. 417
The sky appears blue because billions of air molecules selectively scatter the
shorter wavelengths of visible light more effectively than the longer ones. This
causes us to see blue light coming from all directions.
Fig. 15-4, p. 418
crepuscular rays
The scattering of sunlight by dust and haze produces these white bands of
crepuscular rays.
Fig. 15-7, p. 419
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
The behavior of light as it enters and leaves a more-dense substance,
such as water.
Fig. 15-11, p. 421
Fig. 15-12, p. 422
The Mirage
Inferior mirage
The road in the photo appears wet because blue skylight is bending up into the
camera as the light passes through air of different densities.
Fig. 15-15, p. 424
Inferior mirage
The road in the photo appears wet because blue skylight is bending up into the
camera as the light passes through air of different densities.
Fig. 15-16, p. 424
superior mirage
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.
Fig. 15-17, p. 425
A 22° halo around the sun, produced by the
refraction of sunlight through ice crystals.
Fig. 15-18, p. 425
The formation of a 22° and a 46° halo with column-type
ice crystals.
Fig. 15-19, p. 426
Halo with an upper tangent arc
Fig. 15-20, p. 427
Refraction and dispersion of light through a glass prism.
Fig. 15-21, p. 427
Platelike ice crystals falling with their flat surfaces parallel to the earth
produce sundogs.
Fig. 15-22, p. 427
The bright areas on each side of the sun are sundogs.
Fig. 15-23, p. 428
A brilliant red sun pillar extending upward above the sun, produced by the
reflection of sunlight off ice crystals.
Fig. 15-24, p. 428
Optical phenomena that form when cirriform ice crystal clouds
are present.
Fig. 15-25, p. 429
When you observe a rainbow, the sun is always to your
back.
Fig. 15-26, p. 429
Rainbows
Sunlight internally reflected and dispersed by a
raindrop.
(a)The light ray is internally reflected only when it
strikes the backside of the drop at an angle
greater than the critical angle for water.
(b) Refraction of the light as it enters the drop
causes the point of reflection (on the back of the
drop) to be different for each color.
Hence, the colors are separated from each other
when the light emerges from the raindrop.
Fig. 15-27, p. 430
The formation of a primary rainbow. The observer sees red light from the upper
drop and violet light from the lower drop.
Fig. 15-28, p. 430