Teaching the Electromagnetic Spectrum Using the Sun
Students will explore multi-wavelength movies of the Sun and relate
the wavelengths observed to the physical phenomena.
Main Lesson Concept:
Multiple colors of light allow more complete exploration of complex physical
phenomena such as the active regions of the Sun.
Scientific Question:
Why do astronomers use many filters and telescopes to study the same object?
Pre-Requisite Concepts:
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Visible light consists of the colors red, orange, yellow, green, blue, violet in order from
longest to shortest wavelength.
Frequency is inversely proportional to wavelength and the proportionality constant for light
c
is the speed of light. f =
l
Human eyes cannot detect all colors of light.
False color images are created to represent light emission that is not visible to the eye (such
as X-ray or infrared light) in a way that shows the relative intensity of the light. (Digital
Earth Watch software packages introduce this concept in the context of Landsat imaging and
studying vegetation. http://www.globalsystemsscience.org/software)
Electrons bound in atoms can emit light at certain colors as they transition from a high
energy “orbital” to a low energy “orbital.” The pattern of light observed is unique to that
atom and is called an emission line spectrum. The emitted colors of light are single
wavelengths.
Warm objects emit a continuous spectrum in which all colors of light are produced without
gaps.
Concepts Introduced in This Lesson:
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The energy of one photon of light varies proportionally with frequency.
The electromagnetic spectrum is a continuous sequence from radio waves to gamma rays.
The Sun emits light at many wavelengths.
Different colors of light can be used to explore different physical conditions.
Georgians Experience Astronomy Research in Schools (GEARS) is funded by NASA Office of Education Grant NNX09AH83A and
supported by the Georgia Department of Education, Columbus State University, and Georgia Southern University.
Standards Addressed:
NSES Content Standard D (9-12): Electromagnetic waves include radio waves (the
longest wavelength), microwaves, infrared radiation (radiant heat), visible light, ultraviolet
radiation, x-rays, and gamma rays. The energy of electromagnetic waves is carried in packets
whose magnitude is inversely proportional to the wavelength.
Each kind of atom or molecule can gain or lose energy only in particular discrete amounts and
thus can absorb and emit light only at wavelengths corresponding to these amounts. These
wavelengths can be used to identify the substance.
Required Materials:
JHelioviewer and internet access
Electromagnetic spectrum video from NASA
Engage:
The ‘engage’ part of the lesson should make connections between past and present learning
activities. Teachers are encouraged to highlight a recent solar flare event and ask students
to recall what they heard about the event in the media.
Show students videos of sunspots from March 6-7 2012 X5 flare event in continuous
light and in UV light (JHelioviewer live or exported previously).
Lead in question – which color seems to represent more energetic phenomena?
Explore:
The ‘explore’ part of the lesson provides students with a common base of experiences.
Students gain experience with the JHelioviewer software and begin to focus on the
meanings of the images rather than simply the process of making movies.
Have students explore JHelioviewer and answer the following questions:
1) How many colors are available to include in layers?
2) Which colors seem to represent features closer to the surface of the Sun?
3) What is the naming system for the various colors?
4) Which colors seem to represent more energetic processes?
Explain:
The ‘explain’ part of the lesson should allow students to begin to explain what they are
learning in their own words. In this portion of the lesson, teachers are encouraged to
intersperse introduction of new concepts with opportunities for students to apply these
concepts.
The structure of the exterior of the Sun includes the photosphere, or what we consider the edge
of the Sun which is observable in visible (or white) light. The atmosphere of the Sun extends
well beyond the photosphere as illustrated in this diagram. The atmosphere of the Sun includes
the corona.
Georgians Experience Astronomy Research in Schools (GEARS) is funded by NASA Office of Education Grant NNX09AH83A and
supported by the Georgia Department of Education, Columbus State University, and Georgia Southern University.
Figure from http://www.swpc.noaa.gov/Curric_7-12/ Chapter 2.
We use different parts of the electromagnetic spectrum to explore the atmosphere of the Sun.
 Show video introducing electromagnetic spectrum.
(http://missionscience.nasa.gov/nasascience/ems_full_video.html)
 Relate names of spectrum parts to wavelength.
(http://www.colorado.edu/physics/2000/waves_particles/index.html)
Ask Students To Explain: Which ‘layers’ available in JHelioviewer show the
photosphere? Which show the sunspots? Which show the corona?
Temperature and density conditions in different parts of the Sun’s atmosphere allow
electrons in different elements to become excited and produce emission spectra. The unique
electronic structures of atoms permit identification of individual elements by matching the
specific wavelengths of light observed to the known properties of the elements. Using a filter
which selects a small range of wavelengths allows targeted observations of a region
characterized by a certain temperature since the narrow range of wavelengths are produced only
by atoms with electrons in the appropriate energy levels. Narrowing in on one element is the way
we can explore where a certain temperature region is in the atmosphere. The filters don’t just
select for a color of light; they select for a certain range of physical properties. The filters used
by the Solar Dynamics Observatory that are available in JHelioviewer are targeted at different
parts of the Sun’s atmosphere. See Table 1.
Georgians Experience Astronomy Research in Schools (GEARS) is funded by NASA Office of Education Grant NNX09AH83A and
supported by the Georgia Department of Education, Columbus State University, and Georgia Southern University.
Hydrogen is the simplest element, with only one electron. The structure of the Hydrogen
atom allows electrons to absorb or emit photons of visible light that have energies and
wavelengths as shown in this diagram. (More information about spectral lines:
http://www.colorado.edu/physics/2000/quantumzone/index.html)
(Figure from http://montessorimuddle.org/tag/atoms/)
Some of the allowed changes in energy are represented in the next diagram (for Hydrogen).
(Figure from http://www.physast.uga.edu/~rls/astro1020/ch4/ovhd.html)
Ask Students to Explain: Can electrons in hydrogen atoms emit every color in the
rainbow?
Georgians Experience Astronomy Research in Schools (GEARS) is funded by NASA Office of Education Grant NNX09AH83A and
supported by the Georgia Department of Education, Columbus State University, and Georgia Southern University.
Photons
We think of light as a continuous wave, but light is actually ‘quantized’ into packets or units of a
certain minimum energy that can’t get smaller. The individual packet of light is called a photon.
Each photon has an energy that is inversely proportional to the wavelength or color of the light
hc
(directly proportional to the frequency) E = hf =
where the proportionality constant is
l
Planck’s constant, h = 6.626 x 10-34 J/Hz. Introducing light as a particle can be somewhat
confusing for students as light has been described as a wave. The longer the wavelength of light,
the lower the energy of one photon of that light. This idea of the energy of one photon
depending on the color of light is also confusing as students have equated the ‘brightness’ of
light with the energy of the light source. The power (Watts) produced by a light source is related
to the total number of photons produced over many wavelengths in one second. Each single
photon of light may carry more energy (e.g. ultraviolet light) or less energy (e.g. microwave
light) depending on the color. So light is a particle and wave simultaneously and the measure of
energy of light is related to the total ‘brightness’ and the color of the light.
Photons are related to the observed emission spectrum since in order for the electron to transition
from one energy level to another, it must absorb or emit a photon with exactly the energy of the
difference of the two energy levels. The energy differences between allowed electron energy
states vary from atom to atom which is why the colors of light observed in the spectrum of an
atom are unique to that atom.
Ask Students To Explain: Why the wavelengths of light emitted by the hydrogen atom
electrons as they lose energy are not all the same? Or, why can we see some violet,
green, red, and ultraviolet light from Hydrogen?
Colors of the Sun
The study of the Sun’s atmosphere relies on observations of electron transitions of specific
elements that trace certain density and temperature conditions. The different ‘layers’ available in
JHelioviewer correspond to different wavebands or different colors. The filters (also referred to
as channels) allow only a small range of wavelengths through to the digital camera in a single
snapshot. The filters available on the Solar Dynamics Observatory Telescope are listed below
and the table includes the characteristic temperature traced by the filter or channel. Taking
pictures of the Sun using different filters allows us to study the layers at different temperatures
more clearly.
The notation used by astronomers to designate ionized states is in the 2nd column. The
corresponding chemistry designation is in the 3rd column. The units for wavelength are given in
Angstroms (Å); 1000 Angstroms is 100 nanometers or 1 x 10-7 m. Nearly all the channels listed
here are in the ultraviolet wavelength range (normally considered to be between 100 Å and 4000
Å). The photosphere is what we generally consider the surface of the Sun and observations of the
photosphere are made over a continuous range of wavelengths. You can see from the fifth
column that the temperature in the corona is quite high.
Georgians Experience Astronomy Research in Schools (GEARS) is funded by NASA Office of Education Grant NNX09AH83A and
supported by the Georgia Department of Education, Columbus State University, and Georgia Southern University.
Ask Students to Explain: Why do we use iron instead of nitrogen or hydrogen to study
the high temperature coronal regions in the atmosphere of the Sun? [Iron has 26
electrons when neutral but has many electrons removed in these high temperature
regions. An element such as iron is necessary to probe these high temperature regions
as it is not fully ionized and has electrons bound to the nucleus that still have
identifiable spectral lines. ]
This table is based on the table at http://aia.lmsal.com/public/instrument.htm
Table 1: AIA wavelength bands. (see additional information at end)
Temperature
(K)
Channel name Primary ion(s) Primary ion(s)
Region of atmosphere
white light
continuum
Continuum
Photosphere
5000
1700Å
continuum
Continuum
temperature minimum,
photosphere
5000
304Å
He II
He+1
chromosphere, transition
region
50,000
1600Å
C IV+cont.
C+3+cont.
transition region + upper
photosphere
100,000
171Å
Fe IX
Fe+8
quiet corona, upper
transition region
630,000
193Å
Fe XII, XXIV Fe+11, Fe+23
corona and hot flare
plasma
1,256,000
20,000,000
211Å
Fe XIV
Fe+13
active-region corona
2,000,000
335Å
Fe XVI
Fe+15
active-region corona
2,510,000
94Å
Fe XVIII
Fe+17
flaring regions
6,310,000
131Å
Fe VIII, XX,
Fe+7, Fe +9, Fe +12 flaring regions
XXIII
400,000
10,000,000
16,000,000
Extension: You may choose to explore filters as class activity or teacher demonstration. See
Activity 5 from the NOAA Solar Physics and Terrestrial Effects
(http://www.swpc.noaa.gov/Curric_7-12/Activity_5.pdf).
Elaborate:
The ‘elaborate’ part of the lesson should allow students to extend their conceptual
understanding and to practice using the new concepts and skills. In this portion of the
lesson, students will compare and contrast the quiet and active Sun.
Although the Solar Dynamics Observatory (SDO) is relatively new, the JHelioviewer software
allows access to Solar and Heliospheric Observatory (SOHO) data going back many years. The
Sun is entering a period of maximum activity now. Students can compare the appearance and
features of the Sun recently to images of the Sun from 3 to 5 years ago using SOHO data.
Encourage students to brainstorm the types of comparisons they can make prior to allowing them
to download data. Some types of comparisons might include: number of sunspots visible in a
month, number of prominences in a month, height of prominences, and size of corona.
Georgians Experience Astronomy Research in Schools (GEARS) is funded by NASA Office of Education Grant NNX09AH83A and
supported by the Georgia Department of Education, Columbus State University, and Georgia Southern University.
Evaluate:
The ‘evaluate’ portion of the lesson showcases to both the student and teacher how much a
student has learned and can apply. Some examples of evaluation exercises are provided.
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Create an ordered collage of images that are in order by per photon energy. (File: Save
Screenshot)
Use the AIA wavelength bands table in conjunction with the per photon energy scales to
decide whether the higher temperature regions are being imaged by the highest energy
photon light.
Create a short movie that incorporates two to three layers that represent two to three
different regions of the atmosphere and write a few sentences about which color in their
own image represents the lower temperature and higher temperature regions. (e.g. for the
solar flare video at 131 and 171 Angstroms, the yellow color represents the flaring
region, the green represents where both the 131 and 171 filters detect emission, and the
bluer regions represent the quieter regions without as much flare activity.)
Find X-ray and microwave images of the Sun and compare features observed at these
wavelengths with those observable in ultraviolet. Nobeyama Radio Observatory
maintains a radioheliograph which observes the Sun at 17 GHz and 34 GHz (1.8 cm and
8.8 mm, http://solar.nro.nao.ac.jp/) regularly. A daily image of the Sun at X-ray
wavelengths from the Hinode X-ray Telescope is available on the Current Solar Images
page (http://umbra.nascom.nasa.gov/images/).
Interpret a multi-wavelength image such as the Multiwavelength Milky Way
(http://mwmw.gsfc.nasa.gov/images/mwmw_11a.pdf) and identify regions in the galaxy
where more energetic photons originate.
Georgians Experience Astronomy Research in Schools (GEARS) is funded by NASA Office of Education Grant NNX09AH83A and
supported by the Georgia Department of Education, Columbus State University, and Georgia Southern University.
Additional Information
Solar Dynamics Observatory: http://sdo.gsfc.nasa.gov/
Solar and Heliospheric Observatory: http://sohowww.nascom.nasa.gov/
Solar Terrestrial Relations Observatory: http://stereo.gsfc.nasa.gov/
“The Atmospheric Imaging Assembly (AIA) for the Solar Dynamics Observatory (SDO) is designed to
provide an unprecedented view of the solar corona, taking images that span at least 1.3 solar diameters
in multiple wavelengths nearly simultaneously, at a resolution of about 1 arcsec and at a cadence of 10
seconds or better. The primary goal of the AIA Science Investigation is to use these data, together with
data from other SDO instruments and from other observatories, to significantly improve our understanding
of the physics behind the activity displayed by the Sun's atmosphere, which drives space weather in the
heliosphere and in planetary environments. The AIA will produce data required for quantitative studies of
the evolving coronal magnetic field, and the plasma that it holds, both in quiescent phases and during
flares and eruptions.”
http://aia.lmsal.com/
SOHO: “The Extreme ultraviolet Imaging Telescope (EIT) is an instrument on the SOHO spacecraft
used to obtain high-resolution images of the solar corona in the ultraviolet range. The EIT instrument is
sensitive to light of four different wavelengths: 17.1, 19.5, 28.4, and 30.4 nm, corresponding to light
produced by highly ionized iron (XI)/(X), (XII), (XV), and helium (II), respectively.”
http://en.wikipedia.org/wiki/Extreme_ultraviolet_Imaging_Telescope
Software download: JHelioviewer http://jhelioviewer.org/
Online only interface for solar image viewing: Helioviewer http://www.helioviewer.org/
Sources for images of the Sun
http://sdowww.lmsal.com/
http://umbra.nascom.nasa.gov/images/
http://www.swpc.noaa.gov/today.html
Space Physics and Terrestrial Effects: http://www.swpc.noaa.gov/Curric_7-12/ includes Activity for
building a spectroscope, measuring the luminosity of the Sun and more.
Three Little Pig(ments): Color and Light Science Project. (Filters in the classroom.)
http://www.exploratorium.edu/snacks/cymk/index.html
Acetates can be purchased online. Search on colored acetates for suggested vendors.
Lists of Lines for elements and ionized elements: NIST Atomic Spectra Database – Line Holdings.
http://physics.nist.gov/cgi-bin/ASD/lines_pt.pl
Visible spectral lines for neutral atoms in clickable periodic table:
http://www.colorado.edu/physics/2000/applets/a2.html
Questions or comments about this lesson or GEARS, please contact Zo Webster at
zwebster@alumnae.mtholyoke.edu
GEARS: http://cheller.phy.georgiasouthern.edu/gears
Georgians Experience Astronomy Research in Schools (GEARS) is funded by NASA Office of Education Grant NNX09AH83A and
supported by the Georgia Department of Education, Columbus State University, and Georgia Southern University.