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10 Rainbow Questions

1. Is the inside red?

2. Radius in degrees?

3. Width in degrees?

4. Comparison of light intensity inside outside.

5. Time or Day

6. Direction

7. If 2, where is the second bow?

8. If 2, Is the inside red?

9. If 2, Radius of Second?

10.Are rainbows polarized?

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Blue light more readily “scattered” by air molecules called Rayleigh Scattering; strong function of wavelength blue light in sky has been diverted from some other path with some blue light missing, sun looks yellow/orange/red

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WHY IS THE SKY BLUE ?WHY IS THE SKY BLUE ?

INCOMING SOLAR RADIATION

NITROGEN MOLECULE

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WHY IS THE SKY BLUE ?WHY IS THE SKY BLUE ?

SCATTERING OF BLUE LIGHTSCATTERING OF BLUE LIGHT

SPH4UI Blue Haze & Selective ScatterBlue Haze & Selective Scatter

Plants exude terpenes that react with ozone and can also selectively scatter blue Plants exude terpenes that react with ozone and can also selectively scatter blue wavelengths, creating a blue haze.wavelengths, creating a blue haze. Mountains allow for enough viewing distance to create this needed scatter.Mountains allow for enough viewing distance to create this needed scatter.

SPH4UI Atmospheric Dust & RaysAtmospheric Dust & Rays

Dust and salts are large enough to cause geometric scattering, and change blue Dust and salts are large enough to cause geometric scattering, and change blue skies into hazy white skies.skies into hazy white skies.

Concentrated dust or salts beneath clouds can create white crepuscular rays of Concentrated dust or salts beneath clouds can create white crepuscular rays of sunlight.sunlight.

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Is the night sky blue too?• You bet! Just too dim to perceive

– time exposure at night under moonlight shows this

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You can find blue from scattering in other circumstances as well:water, glaciers, astrophysical reflection nebulae…

SPH4UI Red at Sunrise and SunsetRed at Sunrise and Sunset

Low on the horizon, the sun's light Low on the horizon, the sun's light passes through nearly 12 times more passes through nearly 12 times more atmospheric gas and aerosol, which atmospheric gas and aerosol, which has scattered out most short (blue) has scattered out most short (blue) wavelengths. Longer oranges and wavelengths. Longer oranges and reds then comprise the sunlight, which reds then comprise the sunlight, which reflects from clouds and water.reflects from clouds and water.

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The RainbowThe Rainbow

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Water DropletWater Droplet

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Rainbow ColoursRainbow Colours

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The Angle’sThe Angle’s

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The AngleThe Angle

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rainbow

If sun is higher than 42 degrees, then alas no rainbow (it is below the horizon).

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Rainbows come in pairs…Rainbows come in pairs…

Secondary rainbow has tworeflections. Red now appearslower than blue in the sky.

Beautiful double rainbow in Zion National Park.The primary is brighter, and the color sequenceis reversed from that seen in fainter secondary.

Area between rainbows oftenseen to be darker than elsewhere.

Note: rainbow can exist in foreground.

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PrimaryPrimary

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SecondarySecondary

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Then we have TwoThen we have Two

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QuestionsQuestions• Which general direction will a rainbow be found Which general direction will a rainbow be found

in the evening?in the evening?

• Why don’t you see rainbows during the middle of Why don’t you see rainbows during the middle of the day?the day?

Look East

45 degrees up from your toes is still at the ground.

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The halo, and sun-dogsThe halo, and sun-dogs

• 22° halo around sun due to hexagonal ice crystals– often more noticeable around moon at night (less glare)

• Sun-dogs (parhelia) join halo, level with sun– from horizontally situated ice crystals

• akin to leaves falling in stable horizontal orientation

– colored due to refractive dispersion through ice crystal

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Are Rainbows Polarized?Are Rainbows Polarized?

Any light that is reflected is polarized in the plane. Therefore rainbows are somewhat polarized, about 96%.

SPH4UI Sun-dog geometry

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Glorys and Heiligenschein (shadow-hiding)Glorys and Heiligenschein (shadow-hiding)

• A circular rainbow about the anti-solar direction is called a glory– Sometimes 2–3 colored rings

– often see shadow in middle

– water droplet phenomenon

• The anti-solar point may also get bright due to shadow-hiding– called heiligenschein

– often see from airplane over textured terrain

– no, the person in the photo is not an angel

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Cool Rainbow EffectsCool Rainbow Effects

The pot of Gold?

Primary and Reflected Rainbow

Primary, Secondary, and Reflected Rainbow

Supernumerary

Reflected

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Rainbow at Night