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From Buzz
Putnam:
One of the most common
questions asked by students is “Why is the sky blue?” or “Why is the Sun
yellow?” The answer is found by understanding color science concepts
and some basics of color addition. Assuming that the Sun is “white” as
viewed from space (no atmosphere) and that the three primary colors of
light (red, blue and green in equal hues, saturation levels, etc)
compose the white color that is observed. As the white light enters the
Earth’s atmosphere, some of the blue wavelengths are scattered (Rayleigh
Scattering) allowing the remaining two primary wavelengths to pass
through to the observer. The sky will appear blue and the Sun appears
yellow due to red and green wavelengths (color addition) passing through
the atmosphere to the observer . Thus, the Sun takes on a yellow color
and the Earth’s sky appears blue.
Now enter the planet Mars and the same
question is proposed by students: “What color is the Martian sky” and
“What color will the Martian Sun appear to the astronaut walking on the
surface?” Up to a few years ago, this question was merely a
thought-provoking exercise without much evidence to back up the answer.
The recent successful landing of NASA’s Mars Polar Lander, sent last
year to search for water and organic materials in the northern polar
area of Mars, provides some real evidence. Many photos were sent back
from the Lander and the photo seen here confirms the color science of
the Martian atmosphere.
The sky of Mars has always been known to
have a reddish hue due to the gaseous make-up and the suspended
particulates. But what color would the Martian Sun appear to the
observer? If the Sun once again with its “white” light (3 primary
colors) is incident on the atmosphere and some of the red wavelengths
are scattered, the remaining primary colors of blue and green will pass
through to the observer. Referring to the color addition wheel,
combining blue and green will result in cyan (sometimes referred to as
peacock blue). So the Martian Sun, especially seen as a Martian sunset
will appear cyan. The photo from NASA confirms our color science
concepts! Can you predict the color of a Sun from a planet with a green
sky? I can’t wait to see that magenta Sun from Vulcan!
See more information on
Light Scattering |