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 White and colors White and colors review of fate of visible light passing through the atmosphere review of relationship between wavelength and colors White clouds and scattered light White clouds and scattered light reflection scattering • Thunderstorms appear dark because the clouds (cumulonimbus) are about 10 km deep, scattering most of the light. Blue skies and hazy days Blue skies and hazy days selective scattering effect of scattering particle size crepuscular rays Red suns and blue moons Red suns and blue moons path length of sunlight passing through the atmosphere atmospheric particle effects • The “definition” of a blue moon as two full moons in a single calendar month has nothing to do with atmospheric optics. The mirage: seeing is not believing The mirage: seeing is not believing inferior mirage superior mirage • Mirages are very common and may be seen frequently if you look for them. 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. Superior mirage cold surface, warmer temperature aloft • The proper conditions for a superior mirage are commonly found over water and over snow-covered surfaces. 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. Halos, sundogs, and sun pillars Halos ice crystals dispersion • Halo-producing ice crystals are commonly found in cirrostratus clouds Sundogs hexagonal ice crystals horizontal orientation • Sundogs are commonly seen when cirrostratus clouds are in the sky. Sun pillars reflection phenomenon • Sun pillars can be seen shortly after sunrise or shortly before sunset on very cold days. Rainbows Rainbows water droplet phenomenon reflection and dispersion necessary conditions for a rainbow the primary rainbow The secondary rainbow two internal reflections • A tertiary rainbow also exists, but it is too faint to be seen with the human eye. Coronas and cloud iridescence Coronas and cloud iridescence diffraction The corona necessary conditions Cloud iridescence another water droplet diffraction phenomenon The Glory necessary conditions for viewing • 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.