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Unit 9: Light Page 20
through the sunglasses is a bit Think of intensity as the amount of
dimmer. light over a certain amount of area.
The amount of sunlight that falls
Polarizing
on Venus is greater than for the
sunglasses also
Earth, as Venus is closer to the
reduce darken
sun.
the sky, which
gives you more The intensity decreases as you
contrast between move further away from the sun
light and dark, sharpening the (but it decreases at a rate
images. proportional to the distance
squared). If we placed Earth way
Photographers use polarizing filters
out where Pluto is, then the
to cut out glaring reflections. The
amount of light energy that
image on the right was taken
reaches the distant Earth would be
without a polarizer on the camera.
much, much less.
See the glare?
Phase of Light
When you play the musical note A
on a piano, you have eight
different choices. The A on the low
end is also an A on the higher
octaves. Why is that?
Intensity of Light
The A notes are harmonics of each
You can easily figure out that a car
other, meaning that they are sound
headlight has a higher intensity
waves shifted by a very specific
than a flashlight, because it’s
amount.
brighter. But what if the headlight
Light energy does the same thing,
was 100 miles away? Does the
only it’s called a phase shift. When
intensity change?
two beams of light are out of phase
Astronomers use this idea when
with each other, it’s like playing a
looking at the stars. Just because
G and A on the piano. But when
a star appears brighter doesn’t
they are in phase, it’s like playing
mean it’s more luminous. The
two different A notes.
distance to the star also comes into
play when figuring out stellar The time zones on the Earth are an
example of phase differences.
brightness (which relates directly
When it’s 9am in California, it is
to the star’s temperature).
noon in New York. Even though the
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