the color of the sky - ugs project
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Christian Phan
UGS 302 - Living Color
Professor Nancy Kwallek
Final Project
Sunrise and Sunset: The Colors of the Sky
12.1.14
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When was the last time you really appreciated the brilliance a sunset? Often times we
are too self-occupied to even look at the sky when it happens, but I urge you pay
attention to the world around us. Because when the settings are just right, you will be
rewarded with the purest sensation of color that nature has to offer and if you really look,
you will see the vast influence on color that this ephemeral phenomenon is capable of. This
paper seeks to answer two main questions: 1) What are the colors of the sunset and why?
2) Is there a difference in color between sunrise and sunsets?
The Experiment
For subjective analysis, this study asked 20 participants to answer several questions
and to go observe both a sunrise and a sunset, describing their observations.
What color do you think sunrise and sunsets are? (before observing)
Is there a difference in color between the two? (after observing)
Being shown a number of sunrise/sunset pictures, can you tell which one is which?
(after observing)
The results of the questions were as follows:
Unanimously, all twenty participants described sunrises and sunsets to be red and/or
pinkish in hue
After taking the time to go observe both events, a majority (17/20) of the
participants noticed a change in color from the sunrise to the sunset.
The rest saw no difference in color (3/20)
Being presented with 6 images of half sunrise/half sunset, participants could only
describe what the correct event was with a 35.87% accuracy (36 correct/120 total)
The responses to this questionnaire highlighted some very common misconceptions about
the sky and the suns effect on its color. Listed below are some clarifications and
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explanations on these responses which help to answer the two main questions that this
paper sought to answer:
In addition to what results the questionnaire brought about, the colors of the sky due
to the sun can vary from a hazy yellow (Fig. 1) to a deep, rich and vibrant purple
(Fig. 2) based on the conditions of the atmosphere.
Fig. 1 Fig. 2
Photo credit: Fig. 1 Justin Miller; Fig. 2 Stephen F. Corfidi6
The reason only two colors were described in all the responses most probably stems
from the participants having been sheltered to one or only a few regions where the
conditions in the air lead to only red/pink sunsets. This, coupled with the fact that
they also dont often take the time to observe sunsets or sunrises at the opportune
time means that they dont get the chance to see the more vivid sunrises.
There appears to be a consensus that sunrise and sunset look different based on the
participantsfirst-hand experiences but the truth of the matter was that most of
them could not tell the difference when shown isolated pictures of sunrise/sunset
with no context. Though there are slight differences in the two events, the question
is difficult to answer when shown images because much of the color experienced has
to do with the perception of our eyes and how they change throughout the day.
As far as how the sun affects the color around us, the same fundamental principle of how it
creates color in sunrises and sunsets is what creates color for us at all; its white light
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which shifts creates different colors based on how the light travels. The nuances of just
how this works can be explained through the physics of light.
Color in the Sky
To understand the different colors of sunrise and sunset, we must first understand
why there is color at all in the sky. Firstly, what is color? Color is our minds perception of
reflected light whose wavelength lies in the Visible Light Spectrum. It is our interpretation
of the different facets of what we call white light an amalgamation of all the colors in
essence. Where does the white light come from? Simple the sun. The sun emits white
light constantly, providing energy and light for the whole world. So then why is the sun
yellow? This is another major misconception; the sun isnt actually yellow its white. If you
were to look at it from outer space, you would see a giant white orb.
A white sun in airless, black outer space seen from the International Space Station. Credit: NASA
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Common knowledge only tells us that the sun is yellow because 1) thats how we see it on
Earth and 2) most pictures of the sun have been colorized to fit the socially accepted color.
Using a prism, you can see how sunlight can be broken up into the spectrum of its colors:
red, orange, yellow, green, blue, indigo and violet. When you mix all those colors together,
you get white. Heres the strange part: if look at all the photons coming in, our star is
actually sending the most photons in the green portion of the spectrum. Our Sun appears
yellow to us because of the atmosphere.1The dust, gas, and water molecules in the air
scatter the light rays from the sun and since photons in the higher end of the spectrum
blue, indigo and violet are more likely to be scattered away, while the lower end of the
spectrum red, orange and yellow are less easily scattered, 1we see a yellow sun. Its
especially when the sun gets close to the horizon because its light is getting more and more
distorted by the atmosphere, scattering away more and more of the blue light and leaving
us with greater yellow light. Likewise, when the sun is high in the sky with the least
atmospheric interference, it has a bluer tint to it. This effect is the main reason behind the
different possible colors in the sky. Any adjustment in the way the light hits our vision by
means of scatter, reflection, or refraction can alter the colors and produce magnificent
effects. For example:
Historically this phenomenon has been a large part of weather lore, aiding sailors and
farmers in navigating ships and plant crops. There is an old saying that goesRedsky at
night, sailors delight - red sky in morning, sailors warning.
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Red sky at night, sailors delight:When we see a red sky at night, it means that the setting
sun is sending its light through a high concentration of dust particles, which is indicative of
high pressure and stable air coming in from the west; generally, this means that good
weather will follow.3
Red sky in morning, sailors warning:A red sunrise can mean that a high pressure system
(good weather) has already passed, thus indicating that a storm system (low pressure) may
be moving to the east. A morning sky that is a deep, fiery red can indicate that there is high
water content in the atmosphere. So, rain could be on its way.3
SunriseHistoric NWS Collection, NOAA Sunset highlighting dense cirrus cloudsHistoric NWS
Collection, NOAA.
Another source of color in the sky are volcanic ashes, which can produce a range of hues
and effects based on their current location. It is only when small volcanic particles have
been lofted well into the stratosphere that colorful sunset afterglows appear. Volcanic
particles that remain suspended in the troposphere after an eruption are comparatively
large in size and number. As a result, they attenuate sunlight and otherwise subdue twilight
hues, just like man-made dust and haze. Viewed through a veil of tropospheric volcanic ash,
a sunset is dusky and dull.6
http://www.photolib.noaa.gov/historic/nws/wea00173.htmhttp://www.photolib.noaa.gov/historic/nws/wea00173.htmhttp://www.photolib.noaa.gov/historic/nws/wea00189.htmhttp://www.photolib.noaa.gov/historic/nws/wea00189.htmhttp://www.photolib.noaa.gov/historic/nws/wea00189.htmhttp://www.photolib.noaa.gov/historic/nws/wea00173.htm -
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Is There a Difference?
The study finds that the majority of people clearly see a difference in sunrise and
sunset when they look at them first-hand. However, with these same people, there is a
significant difference in their ability to decipher the two when shown an isolated image of
either of the two. Why is that? While there is some difference between the sunrise and
sunset, the biggest factor in real-life vs image experiences is the human eye. During the
day our eyes become adapted to the daylight and our pupils shrink, this means they wont
allow as much light in by the time sunset arrives. Also they become tired the effect is that
we dont capture all the colors that are really there. At sunrise, our eyes are dark adapted,
so our pupils are wider and let more light in, which lead people to record that colors are
more vibrant and brilliant. The other reason that sunrise appears so different from sunset in
person is that the particles in the air shift throughout the day, producing different effects for
both events. During the day the atmosphere becomes filled with pollution and particles,
which help to scatter the light meaning that sunsets extent of the phenomenon is wider
and covers more of the horizon. By sunrise all the air has settled down and so the sunlight
travels directly to our eyes without being bounced away first.7But an image taken by a
camera may not be able to capture the true subtle color change experienced between them.
In Conclusion
There is a lot more to color in the sky than first meets the eye. Apart from the usual
red/orange/pink sunsets, there exist a myriad of hues produced by the sun ranging from a
dusky yellow to a glowing violet all due to how the light reacts with the particles in our
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atmosphere. Our perception of these events, however, are slightly skewed because of
activity that occurs during the day vs the night: our eyes become tired while pollution
gathers in the air by sunset and they become adapted to the dark while pollution settles
down by sunrise. Whatever the case, the two phenomena have been around for the entirety
of humanity for us to watch in awe. So the next time you notice the colors of the sunset,
just take a moment to think about all that goes into it.
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Sources Referenced:
1. Cain, F. (2013, October 8). What Color is the Sun? Retrieved November 28, 2014,
fromhttp://www.universetoday.com/18689/color-of-the-sun/
2. Allaby, Michael. Weather lore. In Encyclopedia of weather and climate, vol. 2. New
York, Facts on File, c2002. p. 625-636.
3. Lutgens, Frederick K., and Edward J. Tarbuck, 1998: Weather analysis and
forecasting. In The Atmosphere: An Introduction to Meteorology, seventh edition,
Prentice Hall, Upper Saddle River, New Jersey, pp. 278-302.
4. Phan, Christian. "Survey on Sunrise and Sunset." (2014): 1-2. Print.
5. Bohren, C. F., and A. B. Fraser, 1985: Colors of the sky. The Physics Teacher, 23,
267-272 (May).
6. Corfidi, Stephen F. "The Colors of Sunset and Twilight." The Colors of Twilight and
Sunset. NOAA/NWS Storm Prediction Center, 1 Sept. 2014. Web.
.
7. Stewart, Alan, writ. Sunset vs Sunrise: Can you tell the difference?. 2014. Film. 30
Nov 2014.
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