Optical Effects Light and Color In Nature

The Blue Sky Oxygen and Nitrogen molecules in the Air are the right size to scatter blue light best. Thus if you look anywhere but at the Sun you see the scattered, Blue Light.

The Red Sunset The Sunset is red because the light passes through a great distance of air. Blue and other colors are scattered away… Only Red is left in a large quantity.

Rainbows Drops of falling rain can act as a prism refracting the colors of white light in different directions. They send out the violet rays at 42° from the direction the light came in. (copy diagram) Rainbows occur when there is both rain and sun. If you want to see a rainbow stand with the sun behind you and rain in front. Look directly away from the sun (at the anti-solar point). The rainbow is a circle that is 42° away from the ASP. Usually part of the circle is below the horizon and so all you see is a “bow”

Halos Halos are an effect similar to Rainbows, but caused by light refracting in ice crystals They form circles around the light source

Depth in Water Refraction can make things appear where they are not In water they will appear less deep than they are. (copy diagram) This is also why a straight stick stuck in water appears bent.

Total Internal Reflection When light refracts because it speeds up the angle of refraction is larger than the angle of incidence If the angle of incidence is large enough the light will be refracted back into the medium, it will be “Totally internally reflected” Total Internal Reflection is used in optical fibers to keep the light from leaving the fiber

Mirages An Inferior Mirage Occurs when there is a layer of hot air near the ground. Light from the sky and objects in it is totally internally reflected back up And thus appear to be on the ground!

A Superior Mirage Occurs when there is a layer of cool air near the ground. Light from the ground and objects on it is totally internally reflected back down and thus appear to be in the sky!

Sometimes an object is below the horizon and the image floats in air with no visible source

The True Direction of a Celestial Object (The “Higher Sun”) As light enters the Earth’s atmosphere it is refracted If an object is at the Zenith its light is not bent…it is really there. (because the angle of incidence = 0) But if the object is not at the Zenith its light is refracted so that it appears higher than it is. This effect is greatest when closest to the horizon.

The late-setting/early rising Sun or Moon When a celestial object rises or sets its light is bent about.2° up. Thus it will appear above the horizon when in fact it is as much as.2° below it! The Squished Sun/Moon Light from the top of the setting/rising Sun/Moon is refracted less than that from the bottom Thus the Sun or Moon along the Horizon appears “squished” by refraction into an elliptical shape.

The Green Flash

Violet light is refracted the most so when the Sun sets the last color you should see is violet. But Violet, Indigo and Blue are all scattered away by the molecules in the air. So… The Last Color that you can see coming from the Sun is green. “The Green Flash” It is very dim and brief, so it is hard to see.

The Blood Red Moon During a lunar eclipse …just when the Moon should disappear in the Earth’s shadow It turns red Two things make this effect: 1.Light from the Sun is refracted by the earth’s atmosphere so that it reaches the Moon 2.As with the red sunset all the colors have been scattered away except for…..Red! (copy diagram)