Optics of the Atmosphere

Daily Web Guide

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Reading Assignment

Read the Audubon Field Guide to the Weather pp. 155-161, and look at Plates 328-364.

Reminders

Complete the "Racing Eastward" worksheet as a homework assignment, and turn it in as part of your first journal (due Feb. 20). Remember to review class notes carefully to prepare for quizzes! Study before each class. Quizzes may also include questions about reading material assigned for that day and not yet covered in class. Be sure to do the reading assignments for the next class period (see Chernicoff, ch. 18, and Peters, ch 1). Future daily web guides will provide study questions to guide you through new reading, in order better to prepare for quizzes.

Class notes

What the atmosphere does to rays of light

• Reflection
  • Bounces image back the way it came
  • rainbow
• Refraction
  • Bends light like a stick under water
  • halos
• Diffraction
  • Opaque object spreads light around its edges
  • coronas and glories
• Scattering
  • Particles diffuse light in all directions
  • blue sky

Halo

• Halo of 22°
  • Radius in angular degrees measured from observer (AFG, p. 158 top)
  • Refraction of light entering one face of a hexagonal (6-sided) ice crystal, leaving by another.
  • What type of cloud causes halos?
• Halo of 46°
  • Refraction of light entering one face of a hexagonal ice crystal, but leaving by the end (or vice-versa).

Parhelia

• Also called mock suns, sun dogs
  • Parselenae, mock moons, moon dogs
  • Bright spots 22° from the sun or moon
  • Refraction of light through flat ice crystals
  • May accompany halos
• Sun pillars
  • vertical
  • at rising or setting
• Parhelic circle
  • makes cross with a pillar

Rainbow

• Primary rainbow
  • 42° radius, measured from observer
  • centered on a point directly opposite the sun (observe with back to sun)
  • Can you see a rainbow at noon?
  • Single reflection off inside back of raindrop
  • Do you know Roy G. Biv?
    • red, orange, yellow, green, blue, indigo, violet
  • Does a rainy day make you feel blue, or like things are coming up roses?
    • Blue, violet inside; red, yellow outside
• Secondary rainbow
  • 51° radius
  • Double reflection
• Can you see a rainbow in the winter?
• Theodoric of Freiberg, 14th century
  • Model raindrops, spherical flasks
  • Light reflects off back side of raindrops
  • Accounted for both primary and secondary rainbows
• When and where might you see a moonbow?