Why is the Sky Blue?
It is easy to see that the sky is blue. Have you ever wondered why? A lot of other
smart people have, too. And it took a long time to figure it out!
The light from the Sun looks white. But it is really made up of all the colors of the
rainbow.
A prism is a specially shaped crystal. When white light shines through a prism, it is separated into all its colors.
Like energy passing through the ocean, light energy travels in waves, too. Some light
travels in short, "choppy" waves. Other light travels in long, lazy waves. Blue light
waves are shorter than red light waves.
All light travels in a straight line unless something gets in the way
to—

reflect it (like a mirror)

bend it (like a prism)
or scatter it (like molecules of the gases in the atmosphere)
Sunlight reaches Earth's atmosphere and is scattered in all
directions by all the gases and particles in the air. Blue light is
scattered in all directions by the tiny molecules of air in Earth's
atmosphere. Blue is scattered more than other colors because it
travels as shorter, smaller waves. This is why we see a blue sky
most of the time.

Closer to the horizon the sky fades to a lighter blue or white. The sunlight reaching us from low in the sky has
passed through even more air than the sunlight reaching us from overhead. As the sunlight has passed
through all this air, the air molecules have scattered and re-scattered the blue light many times in many
directions. Also, the surface of Earth has reflected and scattered the light. All this scattering mixes the colors
together again so we see more white and less blue.
What Makes a Red Sunset?
As the Sun gets lower in the sky, its light is passing through
more of the atmosphere to reach you. Even more of the blue
light is scattered, allowing the reds and yellows to pass straight
through to your eyes
Sometimes the whole western sky seems to
glow. The sky appears red because larger
particles of dust, pollution, and water
vapor in the atmosphere reflect and scatter
more of the reds and yellows.
Why Do We See in 3-D?
By: Stephanie Pappas, Life's Little Mysteries Contributor, Date: 12 May 2010 Time: 08:28 AM ET
When it comes to seeing in 3-D, two eyes are better than one. To see how 3-D vision works, hold a finger at
arm's length and look at it through one eye, then through the other. See how the image seems to jump? That's
because of binocular disparity, the slight difference between the images seen by each eye.
Binocular disparity is one of the most important pieces of information the visual centers of the brain use to
reconstruct the depth of a scene.
If the object you're trying to view is close to you, the brain uses another clue: convergence, or the angle of
your eyes as you focus on an object. Crossing your eyes will give you an extreme example of the convergence
sensation.
But even without binocular vision, it's
possible to judge depth. Animals without
overlapping visual fields rely heavily on
something called parallax, which is the
difference in speed at which closer and
farther objects seem to move as you pass
them. For example, fence posts along the
side of a highway will fly by, while a grain
silo a quarter-mile from the road will
seem to creep. Our brain has a built-in
processing center for this phenomenon,
according to a 2008 Nature study. An
area behind the ear called the middle
temporal region carries information
about parallax, and may synthesize it
with other depth cues. Other means of
perceiving depth using just one eye
involve cues including object size, parallel
lines that appear to converge, sharper
textures in closer objects, and the way
objects overlap.
Even with all these cues at its disposal,
the brain makes mistakes. Artists can
trick the brain into seeing a 2-D painting
in three dimensions by drawing
converging parallel lines and painting
"closer" objects in greater detail.
Gym class can be a bummer for the visual system, as well: According to a 2008 study in the journal
Proceedings of the National Academy of Sciences, our brains take shortcuts based on previous experience
when judging depth. Because most objects we encounter move relatively slowly, we may misjudge the
distance of fast-moving objects — like a soccer ball headed for our face.
6.4 LIGHT READING IP 1: Light Behavior & 3-D
Name___________________________ Class______ Date_____________ Honors? Yes No Score ________
1. Read the article Why is the Sky Blue? Describe how this concept is related to the behavior of waves
(reflection, refraction, diffraction, & interference). Use complete sentences.
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
2. Remember or re-watch the rainbow video from class: http://www.youtube.com/watch?v=g1UHAPQGkKk
Describe how this concept is related to the behavior of waves (reflection, refraction, diffraction, &
interference). Use complete sentences.
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
____________________________________________________________________________________
3. Read the article Why Do We See in 3-D? Name and describe two different methods that our bodies
and minds use to interpret our 3-dimensional world.
a. ______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
b. ______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
Complete the following math problems (you can leave your answer in exponent form). Here are some example
Add the exponents together.
problems:
611 x 69= 6(11+9)=620
23 x 2-9=23-9=2-6
4. 82 x 85=
5. 611 x 69=
6. 515 x 5-9=
7. 10-8 x 10-12=