1. ATMOSPHERIC OPTICS (Chapter 20)
Sunlight bending through ice crystals in cirriform clouds produces bands of color called sundogs, or parhelia, on both sides of the sun on this cold winter day in Minnesota.
ATMOSPHERIC OPTICS
(Chapter 20)

2. REFLECTION “Normal”=perpendicular to the plane θ1=θ2 Page: 566
FIGURE 20.1 For a ray of light striking a flat, smooth surface, the angle at which the incident ray strikes the surface (the angle of incidence, or u1) is equal to the angle at which the reflected ray leaves the surface (the angle of reflection, or u2). This phenomenon is called Snell’s law.
“Normal”=perpendicular
to the plane
θ1=θ2

3. REFRACTION
Page: 571
FIGURE The behavior of light as it enters and leaves a more-dense substance, such as water.
Less dense to more dense (light slows down) = bend toward normal
More dense to less dense (light speeds up) = bend away from normal

4. Cold air is denser than warm air
Key Facts to Remember:
Cold air is denser than warm air
Longwaves slow down/speed up less than shortwaves
Red = longwave; Blue/Violet = shortwave

5. Starlight Refraction less dense more dense Page: 572
FIGURE Due to the bending of starlight by the atmosphere, stars not directly overhead appear to be higher than they really are. (The angle between positions is highly exaggerated.)
more dense

6. Sunlight Refraction Page: 572
FIGURE The bending of sunlight by the atmosphere causes the sun to rise about two minutes earlier, and set about two minutes later, than it would otherwise. (The angle between the positions is highly exaggerated.)

7. Refraction Red (longwave) bends less Blue (shortwave) bends more
Page: 576
FIGURE Refraction and dispersion of light through a glass prism.

8. DIFFRACTION
bright
dark

9. Inferior Mirage Inferior: image is below actual object
cool
hot
Page: 574
FIGURE Inferior mirage over hot desert sand.
Inferior: image is below actual object
Cooler (denser) air is on the INSIDE of the curve.
Image can be inverted if light from the top of the
tree is bent more than light from the bottom.

10. Inferior Mirage
Page: 574
FIGURE 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.

11. Inferior Mirage

12. Superior Mirage Superior: image is above actual object Page: 574
FIGURE 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.
Superior: image is above actual object

13. Superior Mirage sky warm air horizon refracted cold air actual horizon
Photograph by Carlos Santos

14. SUPERIOR MIRAGE
(FATA MORGANA)
Photograph by David Cartier

15. SUPERIOR MIRAGE (FATA MORGANA) Page: 575
FIGURE 1 The Fata Morgana mirage over water. The mirage is the result of refraction—light from small islands and ships is bent in such a way as to make them appear to rise vertically above the water.

16. GREEN FLASH
Rayliegh Scattered

17. GREEN FLASH (Authoritative green flash info: http://aty.sdsu.edu)
Page: 573
FIGURE The very light green on the upper rim of the sun is the green flash. Also, observe how the atmosphere makes the sun appear to flatten on the horizon into an elliptical shape.
(Authoritative green flash info:

18. Refraction of light through
ICE CRYSTAL OPTICS
Refraction of light through
hexagonal
plates or columns

19. 22-degree and 46-degree Halos Page: 576
FIGURE The formation of a 22° and a 46° halo with column-type ice crystals.

20. 22-degree Halo (Lunar)

21. 22-degree Halo (Solar) Page: 575
FIGURE A 22° halo around the sun, produced by the refraction of sunlight through ice crystals.

22. 22-degree Halo
(Bryan Jones)

23. Parhelion or Sundog

24. Sundogs (Parhelia) Page: 577
FIGURE Platelike ice crystals falling with their flat surfaces parallel to Earth produce sundogs.

25. Parhelia

26. Two Sundogs, Partial 22° Halo, and Parhelic Circle
Page: 577
FIGURE The bright areas on each side of the sun are sundogs.

27. Sun Pillar
Page: 578
FIGURE A brilliant red sun pillar extending upward above the sun, produced by the reflection of sunlight off ice crystals.

28. Sun Pillar Formation

29. Sun Pillar
(Dean Leatherman)

30. ICE CRYSTAL OPTICS Page: 578
FIGURE Optical phenomena that form when cirriform ice crystal clouds are present. (A picture of the circumzenithal arc is in Fig. 2 on p. 581.)

31. FIGURE 19.20 Halo with an upper tangent arc.

32. (Authoritative atmosheric opitics info:

33. (LIQUID) WATER
DROP OPTICS

34. Primary Rainbow Formation
Page: 580
FIGURE The formation of a primary rainbow. The observer sees red light from the upper drop and violet light from the lower drop.

35. Primary Rainbow refraction reflection refraction violet inside
Page: 579
FIGURE Sunlight internally reflected and dispersed by a raindrop. Light rays are internally reflected only when they strike the backside of the drop at an angle greater than the critical angle for water. 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.
violet inside
refraction
red outside

36. Page: 579
FIGURE 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.

38. Secondary Rainbow red inside violet outside Page: 580
FIGURE Two internal reflections are responsible for the weaker, secondary rainbow. Notice that the eye sees violet light from the upper drop and red light from the lower drop.
red inside
violet outside

40. Rare photograph of
“end” of rainbow
How did this happen?
PhotoShop!

41. CORONA
Page: 582
FIGURE Corona around the sun photographed in Colorado. This type of corona, called Bishop’s ring, is the result of diffraction of sunlight by tiny volcanic particles. In this case, the particles were emitted from the volcano El Chichón in 1982.
water or aerosol
droplet

42. Diffraction Rings (Glory, Heiligenschein)
Page: 583
FIGURE Light that produces the glory follows this path in a water droplet.
Surface wave
(diffraction)

43. GLORY

44. GLORY
Page: 583
FIGURE The series of rings surrounding the shadow of the aircraft is called the glory.

45. GLORY

46. Heiligenschein