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Ask
Aubie appears on Wednesdays in the Opelika-Auburn News.
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Aubie encourages elementary school-age children to submit educational
questions to Auburn University’s tiger mascot Aubie. An
AU professor with knowledge in the related field is then tapped
to “help Aubie” answer the question. Questions may
be submitted to askaubie@auburn.edu. |
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QUESTION
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March
2, 2005
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Dear
Aubie,
 Why
is the sky blue?
Maya Krtic, 11
Wrights Mill Road Elementary School
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| ANSWER |
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Helping
Aubie this week is:
Dr. Edward Thomas, associate professor of physics, with Auburn
University's College of Sciences and Mathematics. |
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Dear
Maya,
This
is a great question and one that many people want to know
about! The blue color of the sky is due to sunlight interacting
with the air molecules - nitrogen and oxygen gas - in the
sky.
During the daytime, light from the sun illuminates the Earth.
The visible, white light from the sun is actually made up
of all of the colors, from red to blue. Each specific color
of light is identified by a property known as the wavelength.
Red-colored light has a longer wavelength than the blue-colored
light.
Now, when sunlight passes through the Earth's atmosphere,
it becomes scattered by the molecules in the air. However,
the shorter wavelengths - the blue part of the sunlight -
are scattered much more widely than the longer ones. This
effect is known as Rayleigh scattering. Therefore, when you
look up at the sky on a bright, sunny day, you are seeing
the blue wavelengths of sunlight scattered off of the molecules
in the air - and the sky appears blue!
I'm sure you've noticed that the sky sometimes changes colors
as the sun sets - from blue to orange or even red. This is
because as the sun begins to set, the light must travel farther
through the atmosphere before it gets to you. More of the
light becomes reflected and scattered. As less light reaches
you directly, the sun appears less bright. The color of the
sun itself appears to change, first to orange and then to
red. This is because even more of the short wavelength blues
and greens are now scattered. Only the longer wavelengths
- reds and oranges - are left in the direct beam that reaches
your eyes.
The sky around the setting sun may take on many colors. The
most spectacular shows occur when the air contains many small
particles of dust or water. These particles reflect light
in all directions. Then, as some of the light heads toward
you, different amounts of the shorter wavelength colors are
scattered out. You see the longer wavelengths, and the sky
appears red, pink or orange.
Thanks
for your question,
Aubie and Dr. Thomas
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