Chapter 15: Light, Chapter 15: Light, Color and Color and

Atmospheric Atmospheric OpticsOptics

White and colorsWhite and colors White clouds and scattered lightWhite clouds and scattered light Blue skies and hazy daysBlue skies and hazy days Red suns and blue moonsRed suns and blue moons Twinkling, twilight, and the green flashTwinkling, twilight, and the green flash The mirage: seeing is not believingThe mirage: seeing is not believing Halos, sundogs, and sun pillarsHalos, sundogs, and sun pillars RainbowsRainbows Coronas and cloud iridescenceCoronas and cloud iridescence

White and ColorsWhite and Colors

Review:Review: Nearly half of radiation from sun is Nearly half of radiation from sun is

visible light (what wavelengths are visible light (what wavelengths are longest?)longest?)

Four possible fates of light as it enters Four possible fates of light as it enters atmosphere (absorbed, reflected, atmosphere (absorbed, reflected, scattered, transmitted)scattered, transmitted)

So what wavelengths is all white So what wavelengths is all white light? Black light?light? Black light?

We see using rods and conesWe see using rods and cones

White Clouds and White Clouds and Scattered LightScattered Light

ReflectionReflection – occurs when sunlight bounces off a – occurs when sunlight bounces off a surface at same anglesurface at same angle

ScatteringScattering – occurs when sunlight is deflected in – occurs when sunlight is deflected in all directionsall directions Why is the bottom of thunderstorms dark?Why is the bottom of thunderstorms dark?

Blue Skies and Hazy Blue Skies and Hazy DaysDays

Selective scatteringSelective scattering – ability of molecules to – ability of molecules to scatter one wavelength better than othersscatter one wavelength better than others

The larger the particle, the more they scatter The larger the particle, the more they scatter all wavelengths. Haze is white because of thisall wavelengths. Haze is white because of this

Crepuscular raysCrepuscular rays – scattering of sunlight by – scattering of sunlight by dust and haze to produce white bands of lightdust and haze to produce white bands of light

Red Suns and Blue Red Suns and Blue MoonsMoons

Sun can appear red because it Sun can appear red because it travels through more atmosphere travels through more atmosphere near sunset than at middaynear sunset than at midday

Blue moon and suns can happen if Blue moon and suns can happen if the particle is the same size as the particle is the same size as visible light (scattered red more)visible light (scattered red more)

Volcanoes can cause red suns for Volcanoes can cause red suns for many daysmany days

Fig. 15-8, p. 420

Fig. 15-9, p. 420

The Mirage: Seeing Is The Mirage: Seeing Is Not BelievingNot Believing

RefractionRefraction – bending of light due to – bending of light due to density changesdensity changes

Light that travels from less to more Light that travels from less to more dense loses speed, and vice versadense loses speed, and vice versa

Lights twinkle due to refractionLights twinkle due to refraction Twilight occurs due to refractionTwilight occurs due to refraction

The Mirage: Seeing Is The Mirage: Seeing Is Not BelievingNot Believing

MirageMirage – an image that appears – an image that appears displaced from its true positiondisplaced from its true position

Caused by light moving through Caused by light moving through different air densitiesdifferent air densities

Inferior mirageInferior mirage – images that appear – images that appear lower and inverted from originallower and inverted from original

Superior mirageSuperior mirage – images that – images that appear higher than originalappear higher than original

Inferior MirageInferior Mirage

Warm surface, decreasing Warm surface, decreasing temperatures alofttemperatures aloft

• The proper conditions for an inferior mirage are The proper conditions for an inferior mirage are commonly found over a hot road surface during summer, commonly found over a hot road surface during summer, or over an unfrozen lake on a very cold day. or over an unfrozen lake on a very cold day.

Fig. 15-16, p. 424

Stepped Art

Superior MirageSuperior Mirage

Cold surface, warmer temperature Cold surface, warmer temperature aloftaloft• The proper conditions for a superior mirage are commonlyThe proper conditions for a superior mirage are commonly

found over water and over snow-covered surfaces. found over water and over snow-covered surfaces.

Fig. 15-17, p. 425

Stepped Art

Fata MorganaFata Morgana

Complex vertical temperature profileComplex vertical temperature profile• According to legend, King Arthur’s half-sister, According to legend, King Arthur’s half-sister,

Fata Morgana in Italian, was a fairy enchantress Fata Morgana in Italian, was a fairy enchantress trained by Merlin the Magician. She lived in a crystal trained by Merlin the Magician. She lived in a crystal palace beneath the water and could build fantastic palace beneath the water and could build fantastic castles from thin air.castles from thin air.

HalosHalos HaloHalo – Ring of light encircling sun or – Ring of light encircling sun or

moonmoon Ice crystals refract light to create Ice crystals refract light to create

halohalo DispersionDispersion – breaking up of light into – breaking up of light into

different wavelengths (prism)different wavelengths (prism)

SundogsSundogs Created by hexagonal ice crystals Created by hexagonal ice crystals

oriented horizontallyoriented horizontally Ice crystals act like a prismIce crystals act like a prism

• Sundogs are commonly seen when cirrostratus cloudsSundogs are commonly seen when cirrostratus cloudsare in the sky.are in the sky.

Sun PillarsSun Pillars

Caused by reflection of light off ice Caused by reflection of light off ice crystalscrystals

• Sun pillars can be seen shortly after sunrise orSun pillars can be seen shortly after sunrise orshortly before sunset on very cold days.shortly before sunset on very cold days.

Sun PillarsSun Pillars

RainbowsRainbows Water droplet phenomenonWater droplet phenomenon When sunlight enters rain drop, it refracts and When sunlight enters rain drop, it refracts and

dispersesdisperses Red refracts less than violetRed refracts less than violet This light is reflected off backside of raindrop at This light is reflected off backside of raindrop at

critical anglecritical angle Each wavelength is reflected at different angle to Each wavelength is reflected at different angle to

our eyes (dispersed)our eyes (dispersed) It takes many different raindrops to produced a It takes many different raindrops to produced a

rainbow (each raindrop gives a different rainbow (each raindrop gives a different wavelength)wavelength)

Must face the falling rain with sun at your backMust face the falling rain with sun at your back The primary rainbow, the brightest of the rainbowsThe primary rainbow, the brightest of the rainbows

Fig. 15-26, p. 429

Fig. 15-28, p. 430

The Secondary RainbowThe Secondary Rainbow

Two internal reflections (secondary Two internal reflections (secondary rainbow)rainbow)• A tertiary rainbow also exists, but it is too faint toA tertiary rainbow also exists, but it is too faint to

be seen with the human eye.be seen with the human eye.

Coronas and Cloud Coronas and Cloud IridescenceIridescence

DiffractionDiffraction – bending of light around – bending of light around objectsobjects

CoronaCorona – Bright ring of light around – Bright ring of light around the moon or sunthe moon or sun

Blue appears on inside of ring, red Blue appears on inside of ring, red on outsideon outside

The CoronaThe Corona Need a cloud Need a cloud

that has droplets that has droplets of similar sizeof similar size

New clouds are New clouds are the best corona the best corona producersproducers

Cloud IridescenceCloud Iridescence

IridescenceIridescence - - bright areas bright areas produced by produced by diffractiondiffraction

Associated with Associated with thin clouds thin clouds within 20 within 20 degrees of sundegrees of sun

The GloryThe Glory Sun must be to your back, cloud in Sun must be to your back, cloud in

front of youfront of you• It is very common to see a glory from the windowIt is very common to see a glory from the window

of an airplane. Make sure you are sitting on theof an airplane. Make sure you are sitting on theside opposite the sun.side opposite the sun.