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The only topic-suitability requirement is that the scientific research in question is on a topic related to any of these three major scientific units of our course: physics of light and/or matter, physiology of human colour vision, and chemistry of surface colorants.
NATS 1870A: Understanding Colour
SU 2022
Research Project:
Science Reported in Media vs.
Scholarly Sources
Goals of the Report
− to demonstrate that you are able to research diverse scientific aspects of the topics covered in the course
− to research material at a sufficient depth
− to compare the quantity and quality of research as reported in popular media sources versus original
scholarly research findings
− to communicate your research in a clear and concise manner, with proper English language grammar,
demonstrating that you understand the topics presented
Topics of Research
Since this is a very interdisciplinary course, a wide variety of topics are suitable for this research project.
The only topic-suitability requirement is that the scientific research in question is on a topic related to any
of these three major scientific units of our course: physics of light and/or matter, physiology of human
colour vision, and chemistry of surface colorants. The other requirement is that the research is of an
observational nature (i.e. where quantifiable observations/measurements were taken), rather than of
theoretical nature (i.e. where only computer models and/or simulations were studied, without observational
measurements taken). These are very broad topic categories, to allow you the greatest flexibility in finding a
suitable research article.
What to Submit (home page in eClass):
•
Academic Integrity Quiz
•
Research Project Report in Word format (or other word-editing format)
IMPORTANT DEADLINES:
Allowed Publication Date Range for Media Article:
Project Due Date:
May 1st, 2022 – June 1st, 2022
June 1st, 2022
(Note: there is no publication date requirement on the original scholarly articles, although usually they are
published in a timeframe close to the media article.)
Media articles used outside of your allowed date range will result in a grade of zero assigned to the
media-article component of the project. Late projects will receive a 1 mark (out of 16) per day late
penalty, up to 1 week from the original deadline.
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Stage 1: Complete the ‘Academic Integrity Quiz’
This project is to be completed independently by each student, and by maintaining full academic integrity
standards. Any academic integrity infractions found in reports will be strictly penalized, from zero on the
entire report to any other appropriate penalties as outlined by York policies on academic integrity.
• Before commencing your research, you should complete the SPARK Academic Integrity Tutorial:
https://spark.library.yorku.ca/academic-integrity-what-is-academic-integrity/
•
Complete the Academic Integrity Quiz, located on our course home page in eClass. This quiz must
be completed with a final score of 100% on it. There is no time limit on the quiz, and you may try it
as many times as necessary, in order to achieve complete and accurate understanding of academic
integrity requirements for all course work you submit at York University. Marks for this successful
completion will not be given toward the actual project grade, but a deduction will be made if this
quiz is not completed.
Stage 2: Finding the Media Article
You must find an article from an acceptable news magazine or other popular media news source that
specifically describes the contents of a published scientific research experiment (of a
physical/measurable/observable nature, and not theoretical-only modeling), on any of the appropriate
research topics (see page 1). Note that websites which only ‘explain concepts’ in general (eg: How do
rainbows form? How does light split into colours? etc) are NOT suitable for this project, as they are not
analyzing newly published discovery-based research.
For help with ideas about appropriate key words to use when searching the media sources, look to the
general topics listed in the Schedule. Or, alternatively, you can also simply browse the most recent news
stories posted at these media news sources, in the allowed date range, to find one on a suitable topic.
The following are some examples of acceptable media sources for this project:
Phys.org, SciTechDaily, Science News (sciencenews.org), ScienceDaily, Universal-Sci, Science News
Online, Astronomy Magazine, Universe Today, Portal to the Universe, Science/AAAS, Nature, CBC
News: Technology & Science, Scientific American, Popular Science, National Geographic News,
Science and Technology for Canadians, Maclean’s Magazine, The Toronto Star, Globe and Mail;
plus many others!
Media articles must be at least 1,000 words in length (though longer is better), and
should focus on one primary original research experiment/study, rather than discussing the results of
many different experiments (and/or theoretical papers).
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If you need help with determining the suitability of a particular media article, do
NOT post the specific article title and/or web address in the public eClass discussion forums. Instead, send
an email (including your full name, from your York email account) to the course director at
ns1870to@yorku.ca. You can expect a response within 2 working days, provided in your original email
you’ve also included this required information:
•
What is the URL of your media article?
•
When was this media article published? (if it’s not between May 1st, 2022 to June 1st, 2022 then
it’s NOT suitable)
•
How long is this article? (if it’s not at least 1,000 words of actual article text then it’s NOT
suitable)
•
Which of the major topic units – as listed in our Schedule – do you think it falls into?
•
What is the original scholarly journal article on which this media article is reporting? (provide
URL)
(For all other general questions about the project, post your general questions in the public Research Project
discussion forum in eClass).
HELPFUL TIPS:
•
The York library system allows you access many subscription-based journals, to access
some of the original scholarly articles, from here:
https://ocul-yor.primo.exlibrisgroup.com/discovery/jsearch?vid=01OCUL_YOR:YOR_DEFAULT
(You’re not required to use York Library sources; however it may be needed if the media
article you found is based on a scholarly article published in a subscription-based journal for
which York does have access.)
•
The Steacie Science and Engineering Library is a whole library at York dedicated to science!
(It even has real-life librarians who can help you, including remotely.)
•
Consult the following useful website from the York Library on how to find journal articles:
http://researchguides.library.yorku.ca/journalarticles?hs=a
•
You can easily make electronic copies of web pages by ‘printing’ them to a .pdf file, with a
virtual pdf printer. There are many free programs available that can do this, such as the
PrintFriendly web-based service: www.printfriendly.com
Stage 3: Finding the Scholarly Article
Having found the media article, you must now find the original (primary) scholarly article in which this
research was first reported. The media article itself should mention the names of the researchers (who may
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or may not be the authors of the actual media article itself), the title of their original research article (as
published in the scholarly journal), and where it was originally published. Note that as a York University
student, your library privileges include subscription to an enormous database of journals that normally
require a subscription fee. (If you need help with accessing paid-subscription journals with your York U.
account, contact a librarian.) If you happened to choose an article from a journal to which York does not
have a subscription, then you should look for a new article that is covered by a subscription, instead. You do
not need to pay for any special-access articles for this project.
Stage 4: Your Report: Comparing the Science in Media and Scholarly Articles
After reading both the media and the scholarly article, you will now compare them in your own written
report. To be complete, your report must address all of the following questions.
1. Complete the following identifier table:
Media Article
Research Article
Title of Article
Source of Article
(Publication Name)
Date of Publication
URL to the article
Was the research done by
the author of the article?
Where are the Authors
from (if information is
available)?
Give the name and
location of their place of
work.
Note: the contents of this table do NOT count toward the final word count limit on your report.
2. Provide a précis (short summary) of each article in your own words. A good way to make sure you write
the précis in your own words is to read the article a few times until you feel you understand its content as
much as possible, and then put the article away and write the précis without looking at the article. Don’t
forget to articulate the significance of this particular discovery/experiment/study to the broader field of
science it is contributing to. Once you have written the précis, reread it and the article together to make
sure you have not missed any important points. If your words seem much simpler than those of the
article, so much the better!
3. Describe the structure or format of the article – how is the information presented to the reader? Is the
article divided up into sections, and if so what are they? (This applies to both media and scholarly
articles).
4. For the media article, how are the experimental results presented? (For example, is it just a general
written description, are actual numbers reported, are there tables, graphs, statistics?)
5. Compare the general conclusions of the media article with the general conclusions of the research paper.
Do they differ in any way, and if so, how?
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6. Does either of the articles criticize the data, criticize the conclusions, provide alternate hypotheses or
conclusions to explain the data? If so provide details.
7. Does one article provide criticism or alternate viewpoints that the other article fails to mention? If so,
what are they? (For example, do the authors of the research article mention limitations of their research
and conclusions that are left out of the media article?)
8. Does the title of the media article accurately reflect the content of both the media article and the research
article? (Explain why or why not.)
9. Has this exercise given you any insights into how scientific research is done and reported, or into how
the media covers such research? What do you think is the main advantage and disadvantage of new
scientific research being presented in media and scholarly articles? (Discuss at least 1 advantage and 1
disadvantage for each media and scholarly article.)
Format and Expectations of the Report
•
This is NOT AN ESSAY; therefore, you do not need to have a thesis, or try to ‘prove’ or ‘disprove’
any argument(s). Instead, you are asked to report on the differences between science research as
presented in popular media versus scholarly journals. Your report can simply answer each of the
numbered items as they are presented above, in a numbered sequence. Do NOT include the text of
the questions in your report; simply label each answer with the corresponding question number only.
•
The report should be about 1,500 – 2,000 words, of standard font 12 text, single-spaced.
•
Use the APA style for references and citations. (You will use only 2 sources in your report, so
citation of them should be quite straightforward.)
•
Quoting of the articles themselves should be kept to a minimum, and is NOT to be used as ‘content
substitute’ of your report (even if it is cited). Your report should consist mostly of your own writing.
•
The report should be written with proper English grammar; have your report proofread by someone
else who is not in your class (such as your family or friends), especially if English is not your first
language.
TurnItIn Submission
Note that your report will be submitted through the Turnitin assignment tool in eClass, to review it for any
instances of possible plagiarism. In order to help you learn from such situations first, the originality report
on your submission will be made available to you also, after your first submission, and remain available to
you up to the project’s deadline. You may re-write and re-submit your report as many times as needed, up to
the project’s deadline, ensuring that your own original written work is the final version submitted for formal
evaluation.
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Help – Academic Writing
Academic Writing Guide (at the York University Library)
http://researchguides.library.yorku.ca/awg
Writing Centre at York University (offering free individual writing instruction/tutoring appointments)
SPARK: Student Papers & Academic Research Kit
http://www.yorku.ca/spark/
Help – General Workshops
Check the York Events page to search for any relevant workshops coming up soon:
Visit the Learning Skills section of the CDC website (including workshops):
http://lss.info.yorku.ca/
Page 6 of 6
SUPPLEMENT: ASTRONOMICAL PHOTOS
Examples of star clusters showing stars of different colours
1
STAR CLUSTERS
2
3
4
M50
5
NGC 2266
6
7
Pleiades Cluster
8
M4
9
10
11
Star Cluster R136
12
NGC 5139
13
The Hubble 14
SWEEPS Field
NGC 3603
15
Star Forming Region LH 95
16
NGC 602
17
Open Cluster M25
18
19
SUPPLEMENT: ASTRONOMICAL PHOTOS
Examples of Emission Nebulae
(appearing ‘red’ from the Hα transition in the Hydrogen gas)
1
EMISSION NEBULAE
2
Rosette Nebula
3
Heart Nebula
4
IC 410 Nebula
5
AE Aurigae Nebula
Orion Nebula
6
Tulip Nebula
7
NGC 6357
8
Horsehead Nebula
9
IC 2948: The Running Chicken Nebula
10
IC 2948: The Running Chicken Nebula
11
The Great Carina Nebula
12
NGC 6357
13
National Aeronautics and Space Administration
www.nasa.gov
National Aeronautics and Space Administration
TOUR OF THE
ELECTROMAGNETIC
SPECTRUM
Ginger Butcher, Author
Science Systems and Applications, Inc.
Jenny Mottar, Graphic Design and Layout
Digital Management, Inc.
Dr. Claire L. Parkinson, Editor and Science Advisor
NASA Goddard Space Flight Center
Dr. Edward J. Wollack, Editor and Science Advisor
NASA Goddard Space Flight Center
ACKNOWLEDGEMENTS
This third edition of the Tour of the Electromagnetic Spectrum
was created under contracts to the National Aeronautics and
Space Administration by Science Systems and Applications, Inc.
and Digital Management, Inc.
Special thanks to NASA Science Mission Directorate: Kristen
Erickson and Ming-Ying Wei
Reviewers: Jeannette E. Allen, Max Bernstein, Dr. Marcianna
P. Delaney, Britt Griswold, Dr. Hashima Hasan, Dr. J. E. Hayes,
Dr. Paul Hertz, Dr. Lisa Wainio, and Greg Williams
Additional thanks to: Dr. Eric Brown de Colstoun, Scott Gries,
Dr. David Lindley, Dr. Christopher A. Shuman, Todd E. Toth, and
George Varros
Electronic format and videos available at:
http://science.nasa.gov/ems
Published by National Aeronautics and Space
Administration in Washington, DC.
First edition: 2010, NP-2010-07-664-HQ
Second edition: 2015, NP-2015-06-1938-HQ
Third edition: 2016, NP-2016-05-2159-HQ
ISBN 978-0-9967780-2-2
TOUR OF THE
ELECTROMAGNETIC
SPECTRUM
Introduction to the Electromagnetic Spectrum
2
Anatomy of an Electromagnetic Wave
4
Wave Behaviors
6
Visualization: From Energy to Image
8
Radio Waves 10
Microwaves 12
Infrared Waves 14
Reflected Near-Infrared Waves 16
Visible Light 18
Ultraviolet Waves 20
X-Rays 22
Gamma Rays 24
The Earth’s Radiation Budget 26
Activity: Exploring Remote Sensing 28
Credits 30
2
Tour of the Electromagnetic Spectrum
INTRODUCTION TO THE
ELECTROMAGNETIC
SPECTRUM
When you tune your radio, watch TV, send a text message, or pop popcorn
in a microwave oven, you are using electromagnetic energy. You depend
on this energy every hour of every day. Without it, the world you know
could not exist.
Electromagnetic energy travels in waves and spans a broad spectrum
from very long radio waves to very short gamma rays. The human eye
can only detect only a small portion of this spectrum called visible light.
A radio detects a different portion of the spectrum, and an x-ray machine
uses yet another portion. NASA’s scientific instruments use the full range
of the electromagnetic spectrum to study the Earth, the solar system,
and the universe beyond.
OUR PROTECTIVE ATMOSPHERE
Our Sun is a source of energy across the full spectrum, and its electromagnetic radiation bombards our atmosphere constantly. However,
the Earth’s atmosphere protects us from exposure to a range of higher
energy waves that can be harmful to life. Gamma rays, x-rays, and some
ultraviolet waves are “ionizing,” meaning these waves have such a high
energy that they can knock electrons out of atoms. Exposure to these
high-energy waves can alter atoms and molecules and cause damage to
cells in organic matter. These changes to cells can sometimes be helpful, as when radiation is used to kill cancer cells, and other times not, as
when we get sunburned.
Introduction to the Electromagnetic Spectrum
Seeing Beyond our Atmosphere
NASA spacecraft, such as RHESSI, provide scientists
with a unique vantage point, helping them “see” at
higher-energy wavelengths that are blocked by the
Earth’s protective atmosphere.
RHESSI
ATMOSPHERIC WINDOWS
Electromagnetic radiation is reflected or absorbed mainly by several gases in the Earth’s atmosphere,
among the most important being water vapor, carbon dioxide, and ozone. Some radiation, such as visible light, largely passes (is transmitted) through the atmosphere. These regions of the spectrum with
wavelengths that can pass through the atmosphere are referred to as “atmospheric windows.” Some
microwaves can even pass through clouds, which make them the best wavelength for transmitting
satellite communication signals.
While our atmosphere is essential to protecting life on Earth and keeping the planet habitable, it is not
very helpful when it comes to studying sources of high-energy radiation in space. Sensitive instruments
are positioned above the Earth’s energy-absorbing atmosphere to “see” light from energetic ultraviolet,
x-ray and gamma ray sources. The atmosphere is also a hindrance to studying very low energy radio
waves coming from space, as these waves are reflected by plasma in the Earth’s upper atmosphere.
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Tour of the Electromagnetic Spectrum
ANATOMY OF AN
ELECTROMAGNETIC WAVE
Energy, a measure of the ability to do work, comes in many forms and can transform from one type to another. Examples of stored or potential
energy include batteries and water behind a dam. Objects in motion are examples of kinetic energy. Charged particles—such as electrons and
protons—create electromagnetic fields when they move, and these fields transport the type of energy we call electromagnetic radiation, or light.
WHAT ARE WAVES?
ELECTROMAGNETIC WAVES
Mechanical waves and electromagnetic waves are two important ways
that energy is transported in the world around us. Waves in water and
sound waves in air are two examples of mechanical waves. Mechanical
waves are caused by a disturbance or vibration in matter, whether solid,
gas, liquid, or plasma. Matter that waves are traveling through is called
a medium. Water waves are formed by vibrations in a liquid and sound
waves are formed by vibrations in a gas (air). These mechanical waves
travel through a medium by causing the molecules to bump into each other, like falling dominoes transferring energy from one to the next. Sound
waves cannot travel in the vacuum of space because there is no medium
to transmit these mechanical waves.
Electricity can be static, like the energy that can
make your hair stand on end. Magnetism can also
be static, as it is in a refrigerator magnet. A changing magnetic field will induce a changing electric
field and vice-versa—the two are linked. These
changing fields form electromagnetic waves.
Electromagnetic waves differ from mechanical
waves in that they do not require a medium to propagate. This means that
electromagnetic waves can travel not only through air and solid materials,
but also through the vacuum of space.
Classical waves transfer energy without transporting matter through the
medium. Waves in a pond do not carry the water molecules from place to
place; rather the wave’s energy travels through the water, leaving the water molecules in place, much like a bug bobbing on top of ripples in water.
WAVES OR PARTICLES? YES!
Light is made of discrete packets of energy called photons. Photons
carry momentum, have no mass, and travel at the speed of light. All light
has both particle-like and wave-like properties. How an instrument is
designed to sense the light influences which of these properties are observed. An instrument that diffracts light into a spectrum for analysis is an
example of observing the wave-like property of light. The particle-like nature of light is observed by detectors used in digital cameras—individual
photons liberate electrons that are used for the detection and storage of
the image data.
Anatomy of an Electromagnetic Wave
Electromagnetic Waves
Electromagnetic waves are formed by the vibrations of electric and magnetic fields. These fields are
perpendicular to one another in the direction the wave
is traveling. Once formed, this energy travels at the
speed of light until further interaction with matter.
POLARIZATION
One of the physical properties of light is that it can be polarized. Polarization is a measurement of the electromagnetic field’s alignment. In
the figure above, the electric field (in red) is vertically polarized. Think
of a throwing a Frisbee at a picket fence. In one orientation it will pass
through, in another it will be rejected. This is similar to how sunglasses
are able to eliminate glare by absorbing the polarized portion of the light.
DESCRIBING ELECTROMAGNETIC ENERGY
The terms light, electromagnetic waves, and radiation all refer to the
same physical phenomenon: electromagnetic energy. This energy can be
described by frequency, wavelength, or energy. All three are related mathematically such that if you know one, you can calculate the other two.
Radio and microwaves are usually described in terms of frequency (Hertz),
infrared and visible light in terms of wavelength (meters), and x-rays and
gamma rays in terms of energy (electron volts). This is a scientific convention that allows the convenient use of units that have numbers that are
neither too large nor too small.
FREQUENCY
The number of crests that pass a given point within one second is described as the frequency of the wave. One wave—or cycle—per second
is called a Hertz (Hz), after Heinrich Hertz who established the existence
of radio waves. A wave with two cycles that pass a point in one second
has a frequency of 2 Hz.
WAVELENGTH
Electromagnetic waves have crests and troughs similar to those of ocean
waves. The distance between crests is the wavelength. The shortest
wavelengths are just fractions of the size of an atom, while the longest
wavelengths scientists currently study can be larger than the diameter
of our planet!
ENERGY
An electromagnetic wave can also be described in terms of its energy—in units of measure called electron volts (eV). An electron volt is the
amount of kinetic energy needed to move an electron through one volt
potential. Moving along the spectrum from long to short wavelengths,
energy increases as the wavelength shortens. Consider a jump rope with
its ends being pulled up and down. More energy is needed to make the
rope have more waves.
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Tour of the Electromagnetic Spectrum
WAVE BEHAVIORS
Light waves across the electromagnetic spectrum behave in similar ways. Light can be transmitted, reflected, absorbed, refracted, polarized,
diffracted, and scattered. Specialized instruments onboard NASA spacecraft and airplanes collect data on how waves behave when they interact
with matter. Scientists use these data to learn about the physical and chemical composition of the different types of matter.
When light waves encounter an object,
they are either transmitted through,
reflected, or absorbed depending on
the composition of the object and the
wavelength of the light. When incident
light (incoming light) hits an object and
bounces off, this is an example of reflected energy. Very smooth surfaces
such as mirrors reflect almost all incident light.
The color of an object is actually the color of the light reflected while all
other colors are absorbed. Color, in this case, refers to the different wavelengths of light in the visible light spectrum.
Lasers onboard NASA’s Lunar Reconnaissance Orbiter rely on the reflective property of light waves to map the surface of the Moon. The
instrument measures the time it takes a laser pulse to reach the surface
and return. The longer the response time, the farther away the surface
and lower the elevation. A shorter response time means the surface is
closer or higher in elevation. In this image of the Moon’s southern hemisphere, low elevations are shown in purple and blue, and high elevations
are shown in red and brown.
TOPOGRAPHY OF
THE MOON
Absorption occurs when photons from incident light hit atoms
and molecules and cause them to
vibrate. The more an object’s molecules move and vibrate, the hotter
it becomes. This heat is then emitted
from the object as thermal energy.
Some objects, such as darker colored objects, absorb more incident light
energy than others. For example, black pavement absorbs most visible
and UV energy and reflects very little, while a light-colored concrete sidewalk reflects more energy than it absorbs. Thus, the black pavement is
hotter than the sidewalk on a hot summer day. Photons bounce around
during this absorption process and lose bits of energy to numerous molecules along the way. This thermal energy then radiates in the form of
longer wavelength infrared energy.
Thermal radiation from the energy-absorbing asphalt and roofs in a
city can raise its surface temperature by as much as 10° Celsius. The
Landsat 7 satellite image below shows the city of Atlanta as an island
of heat compared to the surrounding area. Sometimes this warming of
air above cities can influence weather, which is called the “urban heat
island” effect.
INFRARED IMAGE OF ATLANTA
Wave Behaviors
Refraction
Refraction is when light waves change direction as they pass
from one medium to another. Light travels slower in air than
in a vacuum, and even slower in water. As light travels into a
different medium, the change in speed bends the light. Different wavelengths of light are slowed at different rates, which
causes them to bend at different angles. For example, when
the full spectrum of visible light travels through the glass of
a prism, the wavelengths are separated into the colors of the
rainbow. Natural rainbows in the atmosphere are from refraction and reflection.
Diffraction is the bending and spreading of waves around an obstacle.
It is most pronounced when a light
wave strikes an object with a size
comparable to its own wavelength.
An instrument called a spectrometer
uses diffraction to separate light into
a range of wavelengths—a spectrum.
In the case of visible light, the separation of wavelengths through diffraction
results in a rainbow.
A spectrometer uses diffraction (and the subsequent interference) of
light from slits or gratings to separate wavelengths. Faint peaks of energy at specific wavelengths can then be detected and recorded. A graph
of these data is called a spectral signature. Patterns in a spectral signature help scientists identify the physical condition and composition of
stellar and interstellar matter.
The graph below from the SPIRE infrared spectrometer onboard the
ESA (European Space Agency) Herschel space telescope reveals strong
emission lines from carbon monoxide (CO), atomic carbon, and ionized
nitrogen in Galaxy M82.
SPECTRAL SIGNATURE of GALAXY M82
Scattering occurs when light bounces
off an object in a variety of directions.
The amount of scattering that takes
place depends on the wavelength of
the light and the size and structure of
the object.
The sky appears blue because of this
scattering behavior. Light at shorter
wavelengths—blue and violet—is scattered by nitrogen and oxygen as
it passes through the atmosphere. Longer wavelengths of light—red
and yellow—transmit through the atmosphere. This scattering of light
at shorter wavelengths illuminates the skies with light from the blue
and violet end of the visible spectrum. Even though violet is scattered
more than blue, the sky looks blue to us because our eyes are more
sensitive to blue light.
Aerosols in the atmosphere can also scatter light. NASA’s Cloud-Aerosol
Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite
can observe the scattering of laser pulses to “see” the distributions of
aerosols from sources such as dust storms and forest fires. The image
below shows a volcanic ash cloud drifting over Europe from an eruption
of Iceland’s Eyjafjallajökull volcano in 2010.
DISTRIBUTION OF
VOLCANIC ASH
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Tour of the Electromagnetic Spectrum
VISUALIZATION:
FROM ENERGY TO IMAGE
False color, or representative color, is used to help scientists visualize data from wavelengths beyond the visible spectrum. Scientific instruments
onboard NASA spacecraft sense both individual wavelengths and wider regions, or spectral bands, within the electromagnetic spectrum. The instruments direct the electromagnetic energy onto a detector, where individual photons yield electrons related to the amount of incoming
energy. The energy is now in the form of “data,” which can be transmitted to Earth and processed into images.
DIGITAL CAMERA
Digital cameras operate similarly to some scientific instruments. A sensor
in the camera captures the brightness of red, green, and blue light and
records these brightness values as numbers. The three sets of data are
then combined in the red, green, and blue channels of a computer monitor to create a color image.
Red
Green
Blue
Composite
NATURAL COLOR IMAGES
Instruments onboard satellites can also capture visible light data to create natural color, or true color, satellite images. Data from visible light
bands are composited in their respective red, green, and blue channels
on screen. The image simulates a color image that our eyes would see
from the vantage point of the spacecraft.
Red
Green
Blue
Composite
FALSE COLOR IMAGES
Sensors can also record brightness values in regions beyond visible light.
This Hubble image of Saturn was taken at longer infrared wavelengths
and composited in the red, green, and blue channels respectively. The
resulting false-color composite image reveals compositional variations
and patterns that would otherwise be invisible.
2.1 µm
1.8 µm
1.0 µm
False Color Composite
From Energy to Image
Martian Soil
This false-color infrared image from the Thermal
Emission Imaging System (THEMIS) camera onboard
the Mars Odyssey spacecraft reveals the differences
in mineralogy, chemical composition, and structure of
the Martian surface. Large deposits of the mineral olivine appear in the image as magenta to purple-blue.
MARS ODYSSEY
DATA FROM MULTIPLE SENSORS
The composite image on the right of the spiral galaxy Messier 101 combines views from the Spitzer, Hubble, and Chandra space telescopes.
The red color shows Spitzer’s view in infrared light. It highlights the heat
emitted by dust lanes in the galaxy where stars can form. The yellow
color is Hubble’s view in visible light. Most of this light comes from stars,
and they trace the same spiral structure as the dust lanes. The blue color
shows Chandra’s view in x-ray light. Sources of x-rays include milliondegree gas, exploded stars, and material colliding around black holes.
Spitzer
Hubble
Chandra
Such composite images allow astronomers to compare how features are
seen in multiple wavelengths. It’s like “seeing” with a camera, nightvision goggles, and x-ray vision all at once.
Composite
COLOR MAPS
To help scientists visualize a data set of just one range of values, such
as temperature or rainfall, the values are often mapped to a color scale
from minimum to maximum. The “color map” below visualizes sea surface salinity data from the Aquarius satellite using a scale from blue to
white. The blue end of the scale shows the lowest amounts of dissolved
salts in the ocean and the white end shows the highest amounts.
A commonly used color scale has red at one end and blue at the other
creating a “rainbow-like” scale. In some cases these colors do not represent traditional meaning—such as red referring to “bad” or “hot.”
For example, red in the map below is good because it indicates high
amounts of chlorophyll associated with an abundance of microscopic
plants known as phytoplankton that support the ocean ecosystem.
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Tour of the Electromagnetic Spectrum
RADIO WAVES
WHAT ARE RADIO WAVES?
Radio waves have the longest wavelengths in the electromagnetic spectrum. They range from the length of a football to larger than our planet.
Heinrich Hertz proved the existence of radio waves in the late 1880s.
He used a spark gap attached to an induction coil and a separate spark
gap on a receiving antenna. When waves created by the sparks of the
coil transmitter were picked up by the receiving antenna, sparks would
jump its gap as well. Hertz showed in his experiments that these signals
possessed all the properties of electromagnetic waves.
RADIO TELESCOPES
You can tune a radio to a specific wavelength—or frequency—and listen
to your favorite music. The radio “receives” these electromagnetic radio
waves and converts them to mechanical vibrations in the speaker to
create the sound waves you can hear.
Radio telescopes look toward the heavens to view planets, comets, giant
clouds of gas and dust, stars, and galaxies. By studying the radio waves
originating from these sources, astronomers can learn about their composition, structure, and motion. Radio astronomy has the advantage that
sunlight, clouds, and rain do not affect observations.
RADIO EMISSIONS IN THE SOLAR SYSTEM
Radio waves are also emitted by the Sun and planets in our solar system. A day of data from the radio astronomy instrument called WAVES
on the WIND spacecraft recorded emissions from Jupiter’s ionosphere
with wavelengths measuring about fifteen meters (shown below). The
far right of this graph shows radio bursts from the Sun caused by electrons that have been ejected into space during solar flares moving at
20% of the speed of light.
RADIO EMISSIONS
In 1932, Karl Jansky at Bell
Labs revealed that stars and
other objects in space radiate
radio waves.
Since radio waves are longer than optical waves, radio telescopes are
made differently than the telescopes used for visible light. Radio telescopes must be physically larger than optical telescopes in order to
make images of comparable resolution. But they can be made lighter
with millions of small holes cut through the dish since the long radio
waves are too big to “see” them. The Parkes radio telescope, which has
a dish 64 meters wide, cannot yield an image any clearer than a small
backyard optical telescope!
PARKES RADIO
TELESCOPE
Radio Waves
Radio Waves in Space
Astronomical objects that have a changing magnetic
field can produce radio waves. NASA’s STEREO
satellite monitors bursts of radio waves from the
Sun’s corona. Data pictured here show emissions
from a variety of sources including radio bursts from
the Sun, the Earth, and even Jupiter.
STEREO
THE RADIO SKY
A VERY LARGE TELESCOPE
In order to make a clearer, or higher resolution, radio image, radio astronomers often combine several smaller telescopes, or receiving dishes,
into an array. Together, these dishes can act as one large telescope whose
resolution is set by the maximum size of the area. The National Radio
Astronomy Observatory’s Very Large Array (VLA) radio telescope in New
Mexico is one of the world’s premier astronomical radio observatories.
The VLA consists of 27 antennas arranged in a huge “Y” pattern up to 36
km across (roughly one-and-one-half times the size of Washington, DC).
The techniques used in radio astronomy at long wavelengths can sometimes be applied at the shorter end of the radio spectrum—the microwave
portion. The VLA image below captured 21-centimeter energy emissions
around a black hole in the lower right and magnetic field lines pulling gas
around in the upper left.
If we were to look at the sky with a radio telescope tuned to 408 MHz, the
sky would appear radically different from what we see in visible light.
Instead of seeing point-like stars, we would see distant pulsars, starforming regions, and supernova remnants would dominate the night sky.
Radio telescopes can also detect quasars. The term quasar is short for
quasi-stellar radio source. The name comes from the fact that the first
quasars identified emit mostly radio energy and look much like stars.
Quasars are very energetic, with some emitting 1,000 times as much
energy as the entire Milky Way. However, most quasars are blocked from
view in visible light by dust in their surrounding galaxies.
Astronomers identified the quasars with the help of radio data from the
VLA radio telescope because many galaxies with quasars appear bright
when viewed with radio telescopes. In the false-color image below, infrared data from the Spitzer space telescope is colored both blue and
green, and radio data from the VLA telescope is shown in red. The quasar-bearing galaxy stands out in yellow because it emits both infrared
and radio light.
QUASAR IN RADIO & INFRARED
RADIO EMISSIONS NEAR BLACK HOLE
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Tour of the Electromagnetic Spectrum
MICROWAVES
MICROWAVE OVENS
This Doppler-radar image
seen on TV weather news uses
microwaves for local weather
forecasting. Shown here is
Hurricane Claudette’s eye-wall
making landfall.
Microwave ovens work by using microwaves with wavelengths of about
12 centimeters in length to force water and fat molecules in food to
rotate. The interaction of these molecules undergoing forced rotation creates heat, and the food is cooked.
MICROWAVE BANDS
Microwaves are a portion or “band” found at the higher frequency end
of the radio spectrum, but they are commonly distinguished from radio waves because of the technologies used to access them. Different
wavelengths of microwaves (grouped into “sub-bands”) provide different
information to scientists. Medium-length (C-band) microwaves penetrate
through clouds, dust, smoke, snow, and rain to reveal the Earth’s surface.
L-band microwaves, like those used by a Global Positioning System (GPS)
receiver in your car, can also penetrate the canopy cover of forests to
measure the soil moisture of rain forests. Most communication satellites
use C-, X-, and Ku-bands to send signals to a ground station.
Microwaves that penetrate haze, light rain and snow, clouds, and smoke
are beneficial for satellite communication and studying the Earth from
space. A microwave radiometer passively senses microwaves coming
from the Earth/atmosphere system. The Soil Moisture Active Passive satellite provides high accuracy, high resolution global maps of the Earth’s
SOIL
MOISTURE
soil moisture and freeze/thaw states. Soil moisture maps are created
by combining passive microwave radiometer measurements with active
radar measurements.
ACTIVE REMOTE SENSING
Radar technology is considered an active remote sensing system because
it actively sends a microwave pulse and senses the energy reflected
back. Doppler Radar, Scatterometers, and Radar Altimeters are examples
of active remote sensing instruments that use microwave frequencies.
The radar altimeter onboard the joint NASA/CNES (French space agency) Ocean Surface Topography Mission (OSTM)/Jason-2 satellite can
determine the height of the sea surface. This radar altimeter beams
microwaves at two different frequencies (13.6 and 5.3 GHz) at the
sea surface and measures the time it takes the pulses to return to the
spacecraft. Combining data from other instruments that calculate the
SEA
SURFACE
HEIGHT
Microwaves
Arctic Sea Ice
The Japanese Advanced Microwave Scanning Radiometer for EOS (AMSR-E) instrument onboard NASA’s
Aqua satellite can acquire high-resolution microwave
measurements of the entire polar region every day,
even through clouds and snowfall.
spacecraft’s precise altitude and correct for the effect of water vapor
on the pulse can determine the sea surface height within just a few
centimeters!
AQUA
GLOBAL WEATHER PATTERNS
CLUES TO THE BIG BANG
Scientists monitor the changes in sea surface height around the world
to help measure the amount of heat stored in the ocean and predict
global weather and climate events such as El Niño. Since warm water
is less dense than cold water, areas with a higher sea surface tend to
be warmer than lower areas. The sea surface height image (page 12)
shows an area of warm water in the central and eastern Pacific Ocean
that is about 10 to 18 centimeters higher than normal. Such conditions
can signify an El Niño.
In 1965, using long, L-band microwaves, Arno Penzias and Robert
Wilson, scientists at Bell Labs, made an incredible discovery quite by
accident: they detected background noise using a special low-noise antenna. The strange thing about the noise was that it was coming from
every direction and did not seem to vary in intensity much at all. If this
static were from something on our planet, such as radio transmissions
from a nearby airport control tower, it would come only from one direction, not everywhere. The Bell Lab scientists soon realized that they had
serendipitously discovered the cosmic microwave background radiation.
This radiation, which fills the entire universe, is a clue to its beginning,
known as the Big Bang.
PASSIVE REMOTE SENSING
Passive remote sensing refers to the sensing of electromagnetic waves
that did not originate from the satellite or instrument itself. The sensor
is merely a passive observer collecting electromagnetic radiation. Passive remote sensing instruments onboard satellites have revolutionized
weather forecasting by providing a global view of weather patterns and
surface temperatures. A microwave imager aboard NASA’s Global Precipitation Measurement Mission (GPM) can capture data from underneath
storm clouds to reveal precipitation rates over land and ocean.
EAST COAST U.S. SNOWSTORM
The image below from the Wilkinson Microwave Anisotropy Probe
(WMAP) shows a detailed, all-sky picture of the infant universe at
380,000 years of age. This light, emitted 13.7 billon-years ago, is ~2.7
Kelvin today. The observed +/-200 microKelvin temperature variations,
shown as color differences in the image, provide the seeds that grew to
become clusters of galaxies.
MICROWAVE BACKGROUND
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Tour of the Electromagnetic Spectrum
INFRARED WAVES
INFRARED ENERGY
Thermometers placed within
each color of the visible spectrum
reveal an increase in temperature
from blue to red. The light energy
just beyond the visible spectrum,
infrared, is even warmer.
A remote control uses light waves just beyond the visible spectrum of
light—infrared light waves—to change channels on your TV. This region
of the spectrum is divided into near-, mid-, and far-infrared. The region
from 8 to 15 microns (µm) is referred to by Earth scientists as thermal
infrared since these wavelengths are best for studying the longwave
thermal energy radiating from our planet.
DISCOVERY OF INFRARED
COOL ASTRONOMY
In 1800, William Herschel conducted an experiment measuring the difference in temperature between the colors in the visible spectrum. When he
noticed an even warmer temperature measurement just beyond the red
end of the spectrum, he had discovered infrared radiation!
Many objects in the universe are too cool and faint to be detected in
visible light but can be detected in the infrared. Scientists are beginning to unlock the mysteries of cooler objects across the universe such
as planets, cool stars, nebulae, and many more, by studying the infrared
waves they emit.
THERMAL IMAGING
We can sense some infrared energy as heat. Some objects are so hot
they also emit visible light—such as a fire does. Other objects, such as
humans, are not as hot and only emit infrared waves. Our eyes cannot see
these infrared waves but instruments that can sense infrared energy—
such as night-vision goggles or infrared cameras–allow us to “see” the
infrared waves emitting from warm objects such as humans and animals.
The temperatures for the images below are in degrees Fahrenheit.
THERMAL IMAGING
The Cassini spacecraft captured this image of Saturn’s aurora using infrared waves. The aurora is shown in blue, and the underlying clouds are
shown in red. These aurorae are unique because they can cover the entire
pole, whereas aurorae around Earth and Jupiter are typically confined by
magnetic fields to rings surrounding the magnetic poles. The large and
variable nature of these aurorae indicates that charged particles streaming in from the Sun are experiencing some type of magnetism above
Saturn that was previously unexpected.
SATURN’S AURORA IN IR
Infrared Waves
Seeing the Unseen
When we look up at the constellation Orion, we see
only the visible light. But NASA’s Spitzer space telescope was able to detect nearly 2,300 planet-forming
disks in the Orion nebula by sensing the infrared glow
of their warm dust. Each disk has the potential to
form planets and its own solar system.
JAMES WEBB SPACE
TELESCOPE
SEEING THROUGH DUST
MONITORING THE EARTH
Infrared waves have longer wavelengths than visible light and can pass
through dense regions of gas and dust in space with less scattering and
absorption. Thus, infrared energy can also reveal objects in the universe
that cannot be seen in visible light using optical telescopes. The James
Webb Space Telescope (JWST) will have three infrared instruments to
help study the origins of the universe and the formation of galaxies, stars,
and planets.
To astrophysicists studying the universe, infrared sources such as planets are relatively cool compared to the energy emitted from hot stars
and other celestial objects. Earth scientists study infrared as the thermal
emission (or heat) from our planet. As incident solar radiation hits Earth,
some of this energy is absorbed by the atmosphere and the surface,
thereby warming the planet. This heat is emitted from Earth in the form
of infrared radiation. Instruments onboard Earth observing satellites can
sense this emitted infrared radiation and use the resulting measurements
to study changes in land and sea surface temperatures.
A pillar composed of gas and dust in the Carina Nebula is illuminated by
the glow from nearby massive stars shown below in the visible light image from the Hubble Space Telescope. Intense radiation and fast streams
of charged particles from these stars are causing new stars to form
within the pillar. Most of the new stars cannot be seen in the visible-light
image (left) because dense gas clouds block their light. However, when
the pillar is viewed using the infrared portion of the spectrum (right), the
dense gas clouds practically disappear, revealing the baby stars behind
the column of gas and dust.
CARINA NEBULA
Visible Light
There are other sources of heat on the Earth’s surface, such as lava flows
and forest fires. The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard the Aqua and Terra satellites uses infrared data
to monitor smoke and pinpoint sources of forest fires. This information
can be essential to firefighting efforts when fire reconnaissance planes
are unable to fly through the thick smoke. Infrared data can also enable
scientists to distinguish flaming fires from still-smoldering burn scars.
FOREST FIRES IN
NORTHERN CALIFORNIA
Infrared
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Tour of the Electromagnetic Spectrum
REFLECTED
NEAR-INFRARED WAVES
NEAR-INFRARED RADIATION
INFRARED FILM
A portion of radiation that is just beyond the visible spectrum is referred
to as near-infrared. Rather than studying an object’s emission of infrared, scientists can study how objects reflect, transmit, and absorb the
Sun’s near-infrared radiation to observe health of vegetation and soil
composition.
Color Infrared film can record near-infrared energy and can help scientists study plant diseases where there is a change in pigment and
cell structure. These two images show the difference between a color
infrared photo and a natural color photo of trees in a park.
HEALTHY VEGETATION
Our eyes perceive a leaf as green because wavelengths in the green
region of the spectrum are reflected by pigments in the leaf, while the
other visible wavelengths are absorbed. In addition, the components in
plants reflect, transmit, and absorb different portions of the near-infrared
radiation that we cannot see.
Reflected near-infrared radiation can be sensed by satellites, allowing
scientists to study vegetation from space. Healthy vegetation absorbs
blue- and red-light energy to fuel photosynthesis and create chlorophyll.
A plant with more chlorophyll will reflect more near-infrared energy than
an unhealthy plant. Thus, analyzing a plant’s spectrum of both absorption and reflection in visible and in infrared wavelengths can provide
information about the plant’s health and productivity.
HEALTHY LEAF
Infrared Film
Color Film
SPECTRAL SIGNATURES OF VEGETATION
Data from scientific instruments can provide more precise measurements
than analog film. Scientists can graph the measurements, examine the
unique patterns of absorption and reflection of visible and infrared energy, and use this information to identify types of plants. The graph below
shows the differences among the spectral signatures of corn, soybeans,
and Tulip Poplar trees.
Near-Infrared Waves
Helping Farmers
Near-infrared data collected by the Landsat 7
satellite, such as this image of Minnesota, can help
farmers assess the health of their crops. Shades
of red in this image indicate good crop health, and
yellow colors reveal where crops are infested.
LANDSAT 7
ASSESSING VEGETATION FROM SPACE
Data and imagery from the U.S. Geological Survey (USGS) and NASA
Landsat series of satellites are used by the U.S. Department of Agriculture
to forecast agricultural productivity each growing season. Satellite data
can help farmers pinpoint where crops are infested, stressed, or healthy.
SOIL COMPOSITION
PLANETS IN NEAR-INFRARED
Near-infrared data can also help identify types of rock and soil. This image of the Saline Valley area in California was acquired by the Advanced
Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard NASA’s Terra satellite.
This false-color composite of Jupiter combines near-infrared and visiblelight data of sunlight reflected from Jupiter’s clouds. Since methane gas
in Jupiter’s atmosphere limits the penetration of sunlight, the amount of
reflected near-infrared energy varies depending on the clouds’ altitude.
The resulting composite image shows this altitude difference as different
colors. Yellow colors indicate high clouds; red colors are lower clouds;
and blue colors show even lower clouds in Jupiter’s atmosphere. The
Near Infrared Camera and Multi-Object Spectrometer (NICMOS) onboard
NASA’s Hubble Space Telescope captured this image at the time of a rare
alignment of three of Jupiter’s largest moons—Io, Ganymede, and Callisto—across the planet’s face.
Data from ASTER’s visible and near-infrared bands at 0.81 µm, 0.56 µm,
and .66 µm are composited in red, green, and blue creating the falsecolor image below. Vegetation appears red, snow and dry salt lakes are
white, and exposed rocks are brown, gray, yellow, and blue. Rock colors
mainly reflect the presence of iron minerals and variations in albedo
(solar energy reflected off the surface).
SALINE VALLEY, CALIFORNIA
JUPITER IN
NEAR IR
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Tour of the Electromagnetic Spectrum
VISIBLE LIGHT
WAVELENGTHS OF VISIBLE LIGHT
All electromagnetic radiation is light, but we can only see a small portion
of this radiation—the portion we call visible light. Cone-shaped cells in
our eyes act as receivers tuned to the wavelengths in this narrow band of
the spectrum. Other portions of the spectrum have wavelengths too large
or too small and energetic for the biological limitations of our perception.
As the full spectrum of visible light travels through a prism, the wavelengths separate into the colors of the rainbow because each color is
a different wavelength. Violet has the shortest wavelength, at around
380 nanometers, and red has the longest wavelength, at around 700
nanometers.
THE SUN’S CORONA
The Sun is the dominant source for visible-light waves our eyes receive.
The outer-most layer of the Sun’s atmosphere, the corona, can be seen in
visible light. But it is so faint it cannot be seen except during a total solar
eclipse because the bright photosphere overwhelms it. The photograph
below was taken during a total eclipse of the Sun where the photosphere
and chromosphere are almost completely blocked by the moon. The ta-
Isaac Newton’s experiment in 1665
showed that a prism bends visible
light and that each color refracts at
a slightly different angle depending
on the wavelength of the color.
pered patterns—coronal streamers—around the Sun are formed by the
outward flow of plasma that is shaped by magnetic field lines extending
millions of miles into space.
COLOR AND TEMPERATURE
As objects grow hotter, they radiate energy dominated by shorter wavelengths, changing color before our eyes. A flame on a blow torch shifts
from reddish to bluish in color as it is adjusted to burn hotter. In the same
way, the color of stars tells scientists about their temperature.
Our Sun produces more yellow light than any other color because its
surface temperature is 5,500°C. If the Sun’s surface were cooler—say
3,000°C—it would look reddish, like the star Betelgeuse. If the Sun were
hotter—say, 12,000°C—it would look blue, like the star Rigel.
TEMPERATURE OF STARS
TOTAL SOLAR ECLIPSE
Visible Light
Victoria Crater on Mars
The High Resolution Imaging Science Experiment
(HiRISE) camera onboard the Mars Reconnaissance
Orbiter (MRO) captured this spectacular visible light
image of Victoria Crater.
SPECTRA AND SPECTRAL SIGNATURES
Close examination of the visible-light spectrum from our Sun and other
stars reveals a pattern of dark lines—called absorption lines. These
patterns can provide important scientific clues that reveal hidden properties of objects throughout the universe. Certain elements in the Sun’s
atmosphere absorb certain colors of light. These patterns of lines within
spectra act like fingerprints for atoms and molecules. Looking at the
Sun’s spectrum, for example, the fingerprints for elements are clear to
those knowledgeable about those patterns.
Patterns are also evident in a graph of an object’s reflectance. Elements,
molecules, and even cell structures have unique signatures of reflectance. A graph of an object’s reflectance across a spectrum is called a
spectral signature. Spectral signatures of different Earth features within
the visible light spectrum are shown below.
SPECTRAL SIGNATURES OF
EARTH FEATURES
MARS
RECONNAISSANCE
ORBITER
ACTIVE REMOTE SENSING—ALTIMETRY
Laser altimetry is an example of active remote sensing using visible light.
NASA’s Geoscience Laser Altimeter System (GLAS) instrument onboard
the Ice, Cloud, and land Elevation Satellite (ICESat) enabled scientists to
calculate the elevation of Earth’s polar ice sheets using lasers and ancillary data. Changes in elevation over time help to estimate variations in
the amount of water stored as ice on our planet. The image below shows
elevation data over the West Antarctic Ice Streams.
Laser altimeters can also make unique measurements of the heights and
characteristics of clouds, as well as the top and structure of the vegetation canopy of forests. They can also sense the distribution of aerosols
from sources such as dust storms and forest fires.
ANTARCTIC ICE STREAMS
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Tour of the Electromagnetic Spectrum
ULTRAVIOLET WAVES
Johann Ritter’s experiment
was designed to expose
photographic paper to light
just beyond the visible spectrum and prove the existence
of light beyond violet—
ultraviolet light.
ULTRAVIOLET LIGHT FROM OUR SUN
Ultraviolet (UV) light has shorter wavelengths than visible light. Although
UV waves are invisible to the human eye, some insects, such as bumblebees, can see them. This is similar to how a dog can hear the sound of a
whistle just outside the hearing range of humans.
The Sun is a source of the full spectrum of ultraviolet radiation, which
is commonly subdivided into UV-A, UV-B, and UV-C. These are the classifications most often used in Earth sciences. UV-C rays are the most
harmful and are almost completely absorbed by our atmosphere. UV-B
rays are the harmful rays that cause sunburn. Exposure to UV-B rays
increases the risk of DNA and other cellular damage in living organisms.
Fortunately, about 95 percent of the UV-B rays are absorbed by ozone in
the Earth’s atmosphere.
DISCOVERY OF ULTRAVIOLET
Scientists studying astronomical objects commonly refer to different subdivisions of ultraviolet radiation: near ultraviolet (NUV), middle ultraviolet
(MUV), far ultraviolet (FUV), and extreme ultraviolet (EUV). NASA’s SDO
spacecraft captured the image below in multiple wavelengths of extreme
ultraviolet (EUV) radiation. The false-color composite reveals different
gas temperatures. Reds are relatively cool (about 60,000 Celsius) while
blues and greens are hotter (greater than one million Celsius).
Since the Earth’s atmosphere absorbs much of the high-energy ultraviolet radiation, scientists use data from satellites positioned above the
atmosphere, in orbit around the Earth, to sense UV radiation coming from
our Sun and other astronomical objects. Scientists can study the formation
of stars in ultraviolet since young stars shine most of their light at these
wavelengths. This image from NASA’s Galaxy Evolution Explorer (GALEX)
spacecraft reveals new young stars in the spiral arms of galaxy M81.
OUR SUN IN UV
In 1801, Johann Ritter conducted an experiment to investigate the existence of energy beyond the violet end of the visible spectrum. Knowing
that photographic paper would turn black more rapidly in blue light than
in red light, he exposed the paper to light beyond violet. Sure enough, the
paper turned black, proving the existence of ultraviolet light.
ULTRAVIOLET ASTRONOMY
GALAXY M81 IN UV
Ultraviolet Waves
SOLAR DYNAMICS
OBSERVATORY
Solar Prominence
NASA’s Solar Dynamics Observatory
(SDO) spacecraft captured this view of
a dense loop of plasma erupting on the
Sun’s surface—a solar prominence.
The plasma is seen flowing along a
magnetic field.
THE OZONE “HOLE”
Chemical processes in the upper atmosphere can affect the amount of
atmospheric ozone that shields life at the surface from most of the Sun’s
harmful UV radiation. Each year, a “hole” of thinning atmospheric ozone
expands over Antarctica, sometimes extending over populated areas of
South America and exposing them to increased levels of harmful UV rays.
The Dutch Ozone Monitoring Instrument (OMI) onboard NASA’s Aura satellite measures amounts of trace gases important to ozone chemistry
and air quality. The image above shows the amount of atmospheric ozone
in Dobson Units—the common unit for measuring ozone concentration.
These data enable scientists to estimate the amount of UV radiation
reaching the Earth’s surface and forecast high-UV-index days for public
health awareness.
ULTRAVIOLET LIGHT FROM STARS
The Lyman-Alpha Mapping Project (LAMP) onboard the Lunar Reconnaissance Orbiter can peer into permanently shaded craters on the moon by
sensing the faint reflections of UV light coming from distant stars.
MAPPING THE MOON IN UV
AURORAE
Aurorae are caused by high-energy waves that travel along a planet’s
magnetic poles, where they excite atmospheric gases and cause them
to glow. Photons in this high-energy radiation bump into atoms of gases
in the atmosphere causing electrons in the atoms to excite, or move to
the atom’s upper shells. When the electrons move back down to a lower
shell, the energy is released as light, and the atom returns to a relaxed
state. The color of this light can reveal what type of atom was excited.
Green light indicates oxygen at lower altitudes. Red light can be from
oxygen molecules at a higher altitude or from nitrogen. On Earth, aurorae
around the north pole are called the Northern Lights.
JUPITER’S AURORA
The Hubble Space Telescope captured this image of Jupiter’s aurora in
ultraviolet wrapping around Jupiter’s north pole like a lasso.
JUPITER’S AURORA IN UV
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Tour of the Electromagnetic Spectrum
X-RAYS
X-RAYS AND ENERGY
TEMPERATURE AND COMPOSITION
X-rays have much higher energy and much shorter wavelengths than
ultraviolet light, and scientists usually refer to x-rays in terms of their
energy rather than their wavelength. This is partially because x-rays
have very small wavelengths, between 0.03 and 3 nanometers, so small
that some x-rays have wavelengths no longer than the diameter of a
single atom.
The physical temperature of an object determines the wavelength of the
radiation it emits. The hotter the object, the shorter the wavelength of
peak emission. X-rays come from objects that are millions of degrees
Celsius—such as pulsars, galactic supernovae remnants, and the accretion disk of black holes.
DISCOVERY OF X-RAYS
X-rays were first observed and documented in 1895 by German scientist
Wilhelm Conrad Roentgen. He discovered that firing streams of x-rays
through arms and hands created detailed images of the bones inside.
When you get an x-ray taken, x-ray sensitive film is put on one side of
your body, and x-rays are shot through you. Because bones are dense
and absorb more x-rays than skin does, shadows of the bones are left on
the x-ray film while the skin appears transparent.
Our Sun’s radiation peaks in the visual range, but the Sun’s corona is much
hotter and radiates mostly x-rays. To study the corona, scientists use data
collected by x-ray detectors on satellites in orbit around the Earth. Japan’s
Hinode spacecraft produced these x-ray images of the Sun that allow
scientists to see and record the energy flows within the corona.
OUR SUN IN X-RAY
From space, x-ray telescopes collect photons from a given region of the
sky. The photons are directed onto the detector, where they are absorbed
and the energy, time, and direction of individual photons are recorded.
Such measurements can provide clues about the composition, temperature, and density of distant celestial environments. Due to the high energy
and penetrating nature of x-rays, x-rays would not be reflected if they hit
the mirror head on (much the same way that bullets slam into a wall).
X-ray telescopes focus x-rays onto a detector using grazing incidence
mirrors (just as bullets ricochet when they hit a wall at a grazing angle).
NASA’s Mars Exploration Rover, Spirit, used x-rays to detect the spectral
signatures of zinc and nickel in Martian rocks. The Alpha Proton X-Ray
Spectrometer (APXS) uses two techniques, one to determine structure
and another to determine composition. Both of these techniques work
best for heavier elements such as metals.
X-Rays
CHANDRA
Galatic Center & the Solar Cycle
This background mosaic of several Chandra X-ray
Observatory images of the central region of our
Milky Way galaxy reveals hundreds of white dwarf
stars, neutron stars, and black holes. Separately,
the Solar and Heliophysics Observatory (SOHO)
captured these images of the Sun representing
an entire solar cycle from 1996 through 2006.
SUPERNOVA
Since Earth’s atmosphere blocks x-ray radiation, telescopes with x-ray
detectors must be positioned above Earth’s absorbing atmosphere. The
supernova remnant Cassiopeia A (Cas A) was imaged by three of NASA’s
great observatories, and data from all three observatories were used to
create the image shown below. Infrared data from the Spitzer Space Telescope are colored red, optical data from the Hubble Space Telescope are
yellow, and x-ray data from the Chandra X-ray Observatory are green
and blue.
The x-ray data reveal hot gases at about ten million degrees Celsius that
were created when ejected material from the supernova smashed into
surrounding gas and dust at speeds of about ten million miles per hour.
By comparing infrared and x-ray images, astronomers are learning more
about how relatively cool dust grains can coexist within the super-hot,
x-ray producing gas.
SUPERNOVA CAS A
EARTH’S AURORA IN X-RAYS
Solar storms eject clouds of energetic particles toward Earth. These
high-energy particles can be swept up by Earth’s magnetosphere,
creating geomagnetic storms that sometimes result in an aurora. The
energetic charged particles from the Sun that cause an aurora also energize electrons in the Earth’s magnetosphere. These electrons move along
the Earth’s magnetic field and eventually strike the Earth’s ionosphere,
causing x-ray emissions. These x-rays are not dangerous to people on
the Earth because they are absorbed by lower parts of the Earth’s atmosphere. Below is an image of an x-ray aurora by the Polar Ionospheric
X-ray Imaging Experiment (PIXIE) instrument aboard the Polar satellite.
EARTH’S X-RAY AURORA
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Tour of the Electromagnetic Spectrum
GAMMA RAYS
SOURCES OF GAMMA RAYS
GAMMA RAY BURSTS
Gamma rays have the smallest wavelengths and the most energy of any
wave in the electromagnetic spectrum. They are produced by the hottest
and most energetic objects in the universe, such as neutron stars and
pulsars, supernova explosions, and regions around black holes. On Earth,
gamma waves are generated by nuclear explosions, lightning, and the less
dramatic activity of radioactive decay.
Gamma-ray bursts are the most energetic and luminous electromagnetic
events since the Big Bang and can release more energy in 10 seconds
than our Sun will emit in its entire 10-billion-year expected lifetime! Gamma-ray astronomy presents unique opportunities to explore these exotic
objects. By exploring the universe at these high energies, scientists can
search for new physics, testing theories and performing experiments that
are not possible in Earth-bound laboratories.
DETECTING GAMMA RAYS
Unlike optical light and x-rays, gamma rays cannot be captured and
reflected by mirrors. Gamma-ray wavelengths are so short that they can
pass through the space within the atoms of a detector. Gamma-ray detectors typically contain densely packed crystal blocks. As gamma rays
pass through, they collide with electrons in the crystal. This process is
called Compton scattering, wherein a gamma ray strikes an electron and
loses energy, similar to what happens when a cue ball strikes an eight
ball. These collisions create charged particles that can be detected by
the sensor.
COMPTON SCATTERING
If we could see gamma rays, the night sky would look strange and unfamiliar. The familiar view of constantly shining constellations would be
replaced by ever-changing bursts of high-energy gamma radiation that
last fractions of a second to minutes, popping like cosmic flashbulbs,
momentarily dominating the gamma-ray sky and then fading.
NASA’s Swift satellite recorded the gamma-ray blast caused by a black
hole being born 12.8 billion light years away (below). This object is among
the most distant objects ever detected.
GAMMA RAY BURST
Gamma Ray
Visible and UV
Gamma Rays
Brighter colors in the
Cygnus region indicate
greater numbers of gamma
rays detected by the Fermi
gamma-ray space telescope.
FERMI
COMPOSITION OF PLANETS
GAMMA RAY SKY
Scientists can use gamma rays to determine the elements on other
planets. The Mercury Surface, Space Environment, Geochemistry, and
Ranging (MESSENGER) Gamma-Ray Spectrometer (GRS) can measure
gamma rays emitted by the nuclei of atoms on planet Mercury’s surface
that are struck by cosmic rays. When struck by cosmic rays, chemical
elements in soils and rocks emit uniquely identifiable signatures of energy in the form of gamma rays. These data can help scientists look for
geologically important elements such as hydrogen, magnesium, silicon,
oxygen, iron, titanium, sodium, and calcium.
Gamma rays also stream from stars, supernovas, pulsars, and black hole
accretion disks to wash our sky with gamma-ray light. These gamma-ray
streams were imaged using NASA’s Fermi gamma-ray space telescope to
map out the Milky Way galaxy by creating a full 360-degree view of the
galaxy from our perspective here on Earth.
The gamma-ray spectrometer on NASA’s Mars Odyssey Orbiter detects
and maps these signatures, such as this map (below) showing hydrogen
concentrations of Martian surface soils.
HYDROGEN ON MARS
A FULL-SPECTRUM IMAGE
The composite image below of the Cas A supernova remnant shows the
full spectrum in one image. Gamma rays from Fermi are shown in magenta; x-rays from the Chandra Observatory are blue and green. The visible
light data captured by the Hubble Space Telescope are displayed in yellow. Infrared data from the Spitzer space telescope are shown in red; and
radio data from the Very Large Array are displayed in orange.
SUPERNOVA
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Tour of the Electromagnetic Spectrum
THE EARTH’S
RADIATION BUDGET
The energy entering, reflected, absorbed, and emitted by the Earth system are the components of the Earth’s radiation budget. Based on the physics
principle of conservation of energy, this radiation budget represents the accounting of the balance between incoming radiation, which is almost entirely solar radiation, and outgoing radiation, which is partly reflected solar radiation and partly radiation emitted from the Earth system, including the
atmosphere. A budget that’s out of balance can cause the temperature of the atmosphere to increase or decrease and eventually affect our climate.
The units of energy employed in measuring this incoming and outgoing radiation are watts per square meter (W/m2).
Reflected Shortwave
Radiation
Incoming Shortwave
Radiation
INCOMING SOLAR
RADIATION
Reflected by
Atmosphere
Reflected by
Surface
Incoming ultraviolet, visible, and a limited amount of infrared energy (together
sometimes called “shortwave radiation”)
from the Sun drive the Earth’s climate
system. Some of this incoming radiation is
reflected off clouds, some is absorbed by
the atmosphere, and some passes through
to the Earth’s surface. Larger aerosol parAbsorbed by ticles in the atmosphere interact with and
Atmosphere absorb some of the radiation, causing the
atmosphere to warm. The heat generated
by this absorption is emitted as longwave
infrared radiation, some of which radiates
out into space.
ABSORBED ENERGY
The solar radiation that passes through
Earth’s atmosphere is either reflected off
snow, ice, or other surfaces or is absorbed
by the Earth’s surface.
Absorbed Energy
The Earth’s Radiation Budget
Emitted Longwave
Radiation
TERRA
RADIATION AND THE CLIMATE SYSTEM
For scientists to understand climate change, they must also determine
what drives the changes within the Earth’s radiation budget. The Clouds
and the Earth’s Radiant Energy System (CERES) instrument aboard
NASA’s Aqua and Terra satellites measures the shortwave radiation reflected and longwave radiation emitted into space accurately enough
for scientists to use in determining the Earth’s total radiation budget.
Other NASA instruments monitor changes in other aspects of the Earth’s
climate system—such as clouds, aerosol particles, and surface reflectivity—and scientists are examining their many interactions with the
radiation budget.
Atmospheric
Window
Emitted by the
Atmosphere
GREENHOUSE EFFECT
Greenhouse gases in the atmosphere (such as water vapor and carbon
dioxide) absorb most of the Earth’s emitted longwave infrared radiation,
which heats the lower atmosphere. In turn, the warmed atmosphere
emits longwave radiation, some of which radiates toward the Earth’s
surface, keeping our planet warm and generally comfortable. Increasing
concentrations of greenhouse gases such as carbon dioxide and methane increase the temperature of the lower atmosphere by restricting the
outward passage of emitted radiation, resulting in “global warming,” or,
more broadly, global climate change.
EMITTED LONGWAVE RADIATION
Heat resulting from the absorption of incoming shortwave radiation is
emitted as longwave radiation. Radiation from the warmed atmosphere,
along with a small amount from the Earth’s surface, radiates out to space.
Most of the emitted longwave radiation warms the lower atmosphere,
which in turn warms our planet’s surface.
Emitted by Lower
Atmosphere
Emitted by the
Surface
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Tour of the Electromagnetic Spectrum
ACTIVITY
EXPLORING REMOTE SENSING
This lesson simulates the process of remote sensing using surface materials of different colors to represent different ground
coverings on Earth. Light meters are used as an analog for satellite instruments to record data from surfaces representing the different
ground coverings. The lesson will help students understand the role of satellites in remote sensing. Instructors can introduce the
concept of albedo, which is the percentage of the Sun’s radiation that reflects from different surfaces on Earth. Albedo is an important
component of Earth’s radiation budget (see pp. 26–27).
Level: Grades 5–9
CONNECTIONS TO THE NEXT GENERATION
SCIENCE STANDARDS
• Light meters (or an iOS/Android device with a lux meter app).
Disciplinary Core Idea PS4.B: Electromagnetic Radiation. When light
• Copies of this booklet printed for students, loaded onto a mobile
shines on an object, it is reflected, absorbed, or transmitted through the object,
depending on the object’s material and the frequency (color) of the light.
MATERIALS
• Paper or fabric of different colors (about 6–10) to simulate ground
coverings on Earth, including at least one each of a light-tone/white
surface, a dark-tone/black surface, and a medium-tone/gray surface.
Any patterns should be small and even across the surface, such as a
calico print with small flowers.
• Meter sticks.
device, or projected in the classroom. A PDF is available at http://
science.nasa.gov/ems.
• Access to an outdoor area with several types of ground cover (e.g.,
asphalt, grass, bare dirt) (optional).
SET UP
• Place the surface materials in locations around the room. (If outdoors,
identify a space that has several types of ground cover.)
• Divide the students into groups and provide each group with a light
meter and a meter stick.
A MASSIVE WINTER STORM SYSTEM dropped 20 to 30 inches (50 to 70 centimeters) of snow from Tennessee and Georgia to Massachusetts from January
22 to 24, 2016. The Moderate Resolution Imaging Spectroradiometer (MODIS)
on NASA’s Aqua satellite captured a broad view of the eastern United States at
1:30 p.m. EST on January 24, 2016. Image from http://earthobservatory.nasa.
gov/IOTD/view.php?id=87395
Activity: Exploring Remote Sensing
This is a Landsat 8 image of a portion of the Southern
Ocean and the northern Antarctic Peninsula. The
dark open ocean (left) and exposed rock absorb a
high percentage of the Sun’s energy and have a low
albedo. The flowing glaciers and other ice cover
(bright and smooth areas) have high albedos, and the
Larson B embayment (right) is covered with sea ice
(mottled dull gray tone/texture), which has a slightly
lower albedo than the adjacent ice shelf.
LANDSAT 8
EVALUATE
ENGAGE
Show students the satellite image of the eastern United States after a
snowstorm. Ask them what they observe on the image (e.g., cloud cover,
coastlines) and record their answers. Ask what can be inferred (e.g., lack
of clouds over an area suggests a sunny sky there) or what they aren’t
sure of regarding what the image shows (e.g., whether white-colored areas
are clouds or snow). Have students record their answers. Invite students
to select one or two satellite images from this booklet and ask the same
questions. Ask students to share their answers and discuss what kinds of
information we get from these remotely sensed images.
EXPLORE
Demonstrate to students how to use the light meter with the meter stick as
a guide for height. Have students design a method for collecting, analyzing, and communicating their data. Have them determine the parameters
to include in their science journal entries (e.g., headings, data, methods,
predictions, conclusions). They can include predictions on the reflectance of
various materials and compare those to measurements.
EXPLAIN
Ask students to communicate group results. Did they notice any patterns?
How did the values differ between surfaces? What happened to the light as
it interacted with different surfaces? Can they explain any differences in the
light measurements? How did they decide on the height at which they held
the light meter to make measurements? This process will help make student
thinking discernible so both they and the teacher can assess understanding.
Discuss how these measurements are like those of passive remote sensing
instruments on satellites (e.g., the light meter collects light that reflects off
the surface while some light is absorbed—see pp. 12–13). Discuss how
light meters are unlike satellite instruments. For example, light meters used
in this activity measure light in the entire visible range of the electromagnetic spectrum (see pp. 2–3), while most satellites collect data at specific
regions—sometimes called bands—of the visible spectrum as well as parts
of the spectrum beyond visible light (see the back cover).
A simple rubric could be created from the steps above. Did students collect
and record all the parameters that would influence their data (e.g., light
source, height of measurement)? Did they recognize patterns? Did they collect enough data?
Gaining insight into students’ thinking is a good way to scaffold student
learning and monitor their progress. Have each student draw and label
a diagram (visual model) of how satellites and/or the light meters detect
electromagnetic energy. Encourage students to include on their diagrams
features such as the radiation source, the interaction between the radiation
and the surface (i.e., whether the radiation is reflected, absorbed, or scattered), and the detector (e.g., the light meter or a satellite instrument). Have
students share their diagrams with others in order to refine their thinking.
EXTEND
The measurements in this activity correspond to the amount of visible light
being reflected from the surface and detected by the meter. The percentage
of how much of the Sun’s radiation (light) that hits a surface is reflected
without being absorbed is called albedo. Albedo is an important component
of Earth’s radiation budget (see pp. 26–27). Snow, for example, has a high
albedo, meaning that it reflects a lot of the radiation that strikes it.
Observe the sea ice image on the top of page 13. In their science journals, ask students which has a higher albedo: ice or open ocean? (Ice.) As
sea ice melts, what happens to the albedo of the Arctic? Will it increase or
decrease? (Decrease.) What happens when the Sun’s energy is absorbed by
a surface? (It heats up.) What happens as sea ice melts? (The newly exposed
water reflects less and absorbs more of the Sun’s energy. This causes the
water to warm and melt more ice.) This phenomenon is called the ice-albedo
feedback effect. As the surface ice and the sea ice melt, the overall surface
albedo lowers, causing more energy to be absorbed and continuing in a
cycle, thus creating a positive feedback loop.
ADDITIONAL RESOURCES
“Ice Albedo: Bright White Reflects Light” is a short animation (~30 seconds) that illustrates the albedo concept: http://go.usa.gov/cShKA
“Daisy World” is a short video (~4 minutes) that demonstrates the albedo
feedback loop using black and white daisies: http://go.usa.gov/cShKm
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Tour of the Electromagnetic Spectrum
CREDITS
BOOK CREDITS
Author: Ginger Butcher
Graphic Design and Layout: Jenny Mottar
Key Science Advisors and Editors: Dr. Claire L. Parkinson, Dr. Edward J. Wollack
Copyediting: C. Claire Smith
Reviewers: Jeannette E. Allen, Max Bernstein, Dr. Marcianna P. Delaney, Britt Griswold,
Dr. Hashima Hasan, Dr. J. E. Hayes, Dr. Paul Hertz, Dr. Lisa Wainio, and Greg Williams
Special thanks to NASA Science Mission Directorate: Kristen Erickson
and Ming-Ying Wei
Additional thanks to: Dr. Eric Brown de Colstoun, Scott Gries, Dr. David Lindley,
Dr. Christopher A. Shuman, Todd E. Toth, and George Varros
First edition created under the HITSS contract to NASA Headquarters by InDyne, Inc.
and V! Studios, Inc.
IMAGE CREDITS
Inside Cover: Waves, Flavio Takemoto; Page 2–3: Communication Tower, Mihai Andoni; Radio, Peter Huys; Microwave Oven, Kriss Szkurlatowski; Remote Control, Bartek Ambrozik;
Eye, Flavio Takemoto; Page 4: Waves black background, Jana Kollarova; Waterdrop, iStock Photo; Page 6: Topography of the Moon, NASA/Goddard; Atlanta in Infrared, NASA images
by Marit Jentoft-Nilsen, based on Landsat-7 data; Ice background, Elisabeth Sophia Fuchs; Page 7: Spectrograph of Galaxy 3C 326, Troy Benesch; Volcanic Ash Distribution, NASA/
GSFC/LaRC/JPL, MISR Team; Page 8: Balloon Photo, iStock Photo; Saturn Visible Light, NASA and The Hubble Heritage Team (STScI/AURA) Acknowledgment: R.G. French (Wellesley
College), J. Cuzzi (NASA/Ames), L. Dones (SwRI), and J. Lissauer (NASA/Ames); Saturn False Color, NASA/JPL/STScI; Page 9: Messier 101 Galaxy, NASA, ESA, CXC, JPL, Caltech and
STScI; Sea Surface Salinity, NASA/Goddard Space Flight Center Scientific Visualization Studio; Chlorophyll, NASA/GSFC; Page 10: Karl Jansky’s Radio Telescope, Image courtesy of
NRAO/AUI; Solar Radio Bursts, NASA/GSFC Wind/Wave, Michael L. Kaiser; Parkes Radio Telescope, Ian Sutton; Page 11: Radio Emission Near Black Hole, VLA & NRAO, Farhad YusefZedeh et al. Northwestern; Quasar in Radio & Infrared, NASA/JPL-Caltech/A. Martinez-Sansigre (Oxford University); Page 12: Soil Moisture, NASA/JPL-Caltech/GSFC; Doppler Radar,
NOAA; Sea Surface Height, NASA/JPL Ocean Surface Topography Team; Page 13: Arctic Sea Ice from AMSR-E, NASA/Goddard Space Flight Center Scientific Visualization Studio;
East Coast U.S. Snowstorm, NASA’s Scientific Visualization Studio. Data provided by the joint NASA/JAXA GPM mission; WMAP Microwave Background, NASA/WMAP Science Team;
Page 14: Thermal Imaging, Courtesy NASA/JPL-Caltech; Hershel’s Experiment, Troy Benesch; Saturn’s Aurora in IR, Cassini VIMS Team, JPL, ESA, NASA; Page 15: Spitzer image of
Orion in Infrared & James Webb Telescope, Thomas Megeath (Univ. Toledo) et al., JPL, Caltech, NASA; Carina Nebula, NASA, ESA, and the Hubble SM4 ERO Team; Forest Fires in
Northern California, NASA image by Jeff Schmaltz, MODIS Rapid Response Team; Page 16: E. coli, Rocky Mountain Laboratories, NIAID, NIH; Healthy Leaf, Jeff Carns; Infrared and
Natural Color Film photos, Ginger Butcher; Page 17: Minnesota Crops, NASA image created by Jesse Allen, using Landsat data provided by the United States Geological Survey;
Saline Valley California, NASA, GSFC, MITI, ERSDAC, JAROS, and the U.S./Japan ASTER Science Team; Jupiter in Near Infrared, NASA and E. Karkoschka (University of Arizona);
Page 18: Soap bubble, iStock; Sun’s Corona, Courtesy of Miloslav Druckmüller, Martin Dietzel, Peter Aniol, Vojtech Rušin; Sun Image, Courtesy of SOHO/[instrument] consortium.
SOHO is a project of international cooperation between ESA and NASA; Prism Image, Troy Benesch; Page 19: Victoria Crater on Mars, NASA/JPL/University of Arizona; Antarctic Ice
Streams, NASA/Goddard Space Flight Center; Page 20: Rhinovirus, iStock; Ultraviolet waves, NASA/SDO/AIA; Our Sun in UV, NASA/Goddard/SDO AIA Team; Galaxy M81 in UV, NASA/
JPL-Caltech; Ritter’s Experiment, Troy Benesch; Page 21: Solar Prominence, NASA image and animation from the Goddard Space Flight Center Scientific Visualization Studio and
the Solar Dynamics Observatory; Mapping the Moon in UV, Kurt Retherford, LRO LAMP; Ozone Hole, NASA; Jupiter’s Aurora in UV, John Clarke (University of Michigan) and NASA;
Page 22: Our Sun in X-Ray, Hinode JAXA/NASA/PPARC; Mars Rover, Jeff Carns; Page 23: Galactic Center, NASA/UMass/D.Wang et al.; Sun images from SOHO—EIT Consortium:
NASA/ESA; Supernova, NASA/CXC/SAO; Optical: NASA/STScI; Infrared: NASA/JPL-Caltech/Steward/O.Krause et al.; Earth’s X-Ray Aurora, POLAR, PIXIE, NASA; Page 24: Gamma Ray
Burst, NASA/Swift/Stefan Immler, et al.; Page 25: Fermi Gamma Ray Sky and Fermi spacecraft, NASA/DOE/International LAT Team; Hydrogen on Mars, NASA/Goddard Space Flight
Center Scientific Visualization Studio; Supernova, NASA/DOE/Fermi LAT Collaboration, CXC/SAO/JPL-Caltech/Steward/O. Krause et al., and NRAO/AUI; Page 28: Northern Antarctica
Peninsula Landsat image, Dr. Christopher A. Shuman; Snowstorm, NASA image by Jeff Schmaltz, LANCE/EOSDIS Rapid Response; Page 29: LANDSAT 8, NASA/Goddard Space Flight
Center Conceptual Image Lab; Back Cover: Waves, Flavio Takemoto
ACTIVITY: EXPLORING REMOTE SENSING
This lesson was developed by Ed Robeck, Director of the Center for Geoscience
and Society at the American Geosciences Institute, with generous editorial support from Ginger Butcher at Science Systems and Applications, Inc. (SSAI), and
Cassie Soeffing at the Institute for Global Environmental Strategies (IGES). The
activity is based on a laboratory exercise originally developed by Drs. Mara Chen
and Daniel Harris at Salisbury University, and on
a manual of activities developed by Dr. Alexandria
Guth at Michigan Technological University, which
is available on AGI’s Earth Science Week Web site
at http://www.earthsciweek.org/visualizations.
ELECTROMAGNETIC SPECTRUM
COMPANION VIDEOS
Eight videos covering the spectrum plus an introduction to electromagnetic
waves are available at http://science.nasa.gov/ems.
Videos produced under the HITSS contract to NASA Headquarters by InDyne,
Inc., and V! Studios, Inc., by Troy Benesch, Mike Brody, Ginger Butcher, Jeff
Carns, Jack Elias, Kendall Haven, and Ron Mochinski, with NASA science
advisors and editors Dr. Claire Parkinson and Dr. Edward J. Wollack.
Credits
UNIT CONVERSION SCALE
As noted on page 5, electromagnetic waves can be described by their frequency, wavelength, or energy. Radio and microwaves are usually described
in terms of frequency (Hertz), infrared and visible light in terms of wavelength (meters), and x-rays and gamma rays in terms of energy (electron volts).
This is a scientific convention that allows the use of the units that are the most convenient with numbers not too large or too small. For comparison, the
various wavelengths described in this booklet are all expressed in meters in this table.
Discipline Units
Alternate Unit
Length (meters)
Sci Notation (meters)
10 kHz
30 kilometer
30000
3.0E+04
100 kHz
3.0 kilometer
3000
3.0E+03
1 MHz
0.3 kilometer
300
3.0E+02
1 GHz
30 centimeter
0.3
3.0E-01
1.4 GHz
21 centimeter
0.21
2.1E-01
1.0 millimeter
300 GHz
0.001
1.0E-03
100 microns
100 micrometer
0.0001
1.0E-04
50 microns
50 micrometer
0.00005
5.0E-05
20 microns
20 micrometer
0.00002
2.0E-05
1000 nanometers
1.0 micrometer
0.000001
1.0E-06
5000 Angstrom
500 nanometer
0.0000005
5.0E-07
1000 Angstrom
100 nanometer
0.0000001
1.0E-07
500 Angstrom
50 nanometer
0.00000005
5.0E-08
100 Angstrom
10 nanometer
0.00000001
1.0E-08
1 kev
12 Angstrom
0.0000000012
1.2E-09
10 kev
1.2 Angstrom
0.00000000012
1.2E-10
100 kev
0.12 Angstrom
0.000000000012
1.2E-11
1 Mev
1200 femtometer
0.0000000000012
1.2E-12
1 Gev
1.2 femtometer
0.0000000000000012
1.2E-15
Size Comparison
Height of the Statue
of Liberty
Size of a baseball
Diameter of a
human hair
Thickness of a soap
bubble membrane
Diameter of an atom
Diameter/nucleus
FRONT COVER
Cover image shows the Chandra Spacecraft, the Ozone hole image by Aura’s OMI instrument, the Blue Marble image of Earth from Terra’s MODIS
instrument, and pictured left to right Arno Penzias, Wilhelm Roentgen and Issac Newton.
BACK COVER
Missions and instruments mentioned in the text are displayed in this chart.
31
SELECTED NASA MISSIONS & THE ELECTROMAGNETIC SPECTRUM
ISBN 978-0-9967780-2-2
NP-2016-05-2159-HQ
9 780996 778022
90000
