NOVA scienceNOW: Space Storms
Make a concept map of the aurora-formation process. The northern lights, or auroras, are the end result of a set of complex interactions between the sun and Earth. To familiarize students with terminology and the cause-and-effect relationships involved with aurora formation, have them construct a concept map. Before beginning the exercise, make a handout, one for each pair of students, of the following terms.
- Auroral zone
- Coronal mass ejections
- Earth's ionosphere
- Earth's magnetosphere
- Geomagnetic storms
- Magnetic field lines
- Magnetic reconnection
- Northern lights
- Solar activity
- Solar flares
- Solar wind
- Space weather
- Tell the class that these 12 terms, plus Earth and sun, are part of the process that produces the northern lights.
- Have students find definitions on the Web.
- Ask the pairs to consider the relationships among the terms and connect related terms with arrows.
- Next, as a class, make a concept map.
- Draw a sun and an Earth on opposite sides of the board.
- Have student pairs call out their terms connections and draw connecting arrows.
- Have students then decide which verbs or phrases should connect terms to one another.
- Save the finished concept map and revisit it after viewing the segment.
Below is one example of how the terms could be connected in a concept map:
Model Earth's magnetosphere with a bar magnet and iron filings.
Earth's magnetic field acts similarly to that of an ordinary bar magnet. However, rather than having the symmetric dipole shape produced by a bar magnet, Earth's magnetic field is asymmetric due to interactions with the solar wind, which is composed of high-energy charged particles (mostly electrons and protons) ejected from the sun. This wind streams through space at velocities between 300 and 700 km/s, carrying with it the sun's magnetic field. The solar wind compresses Earth's magnetic field lines on the day side (facing the sun) and elongates field lines on the night side (away from the sun) into a teardrop-shaped tail. The size and shape of Earth's magnetosphere fluctuates with changes in the solar wind. Earth's magnetic field shields the planet's surface from most of the charged particles of the solar wind. However, some high-energy particles leak into the magnetosphere and eventually collide with gases in the atmosphere to produce the northern lights.
|Safety Warning: Wear goggles, and have students wear goggles, when performing the activities and handling the materials below.
Have students make a simple model of Earth's magnetic field using ordinary bar magnets and iron filings. Divide the class into small groups. Supply each student with safety goggles and the following materials and instructions (or wear goggles yourself and perform the steps as a demonstration):
- 2 bar magnets with N (north) and S (south) labels
- plastic wrap
- masking tape
- iron filings (in a shaker similar to a salt shaker)
- shoebox lid or thin plastic tray
- overhead transparency (if necessary, cut to fit inside lid or tray)
Put on the safety goggles. Wrap each bar magnet in a layer of plastic wrap to prevent iron filings from sticking to them. Lay one of the magnets on a table noting the position of the north and south labels. This magnet represents Earth. Place the shoebox lid or tray, with its flat side down, on top of the magnet. A little at a time, sprinkle the iron filings generously and evenly over the surface of the shoebox lid or tray. Carefully wipe any extra filings from your hands. Have students sketch how the iron filings arrange themselves in the magnetic field.
Carefully place an overhead transparency on top of the iron filings. Pick up the second magnet (away from the box lid) so as not to disturb the filings. Hold it about an inch above, and parallel to, the first magnet (Earth's magnetic field), but with the opposite orientation of north and south. This magnet represents the solar wind. Slowly sweep the "solar wind" over the shoebox lid from one side to the other. Have students make a new sketch that shows how the iron filings arrange themselves due to the magnetic fields of both bar magnets. Have students describe what happened to the iron filings? (Explain that the solar wind magnet distorts the shape created by the iron filings similar to the way the real solar wind distorts Earth's magnetic field–the day side will be slightly compressed and the night side slightly elongated. Results will vary depending on the strength of the magnets and the speed at which the "solar wind" streams past "Earth.")
Point out that the bar-magnet model is two dimensional, while Earth's magnetic field is three dimensional. Consider using a globe to reinforce this point by indicating how the magnetic lines of force surround Earth. On the board, sketch the symmetric magnetic field of a bar magnet and the asymmetric magnetic field of Earth. Use the images at image.gsfc.nasa.gov/poetry/educator/litho7.jpg as a guide.
Observe the spectral lines of different gases. The beautiful colored lights of the aurora arise from electrically excited atoms and molecules in Earth's ionosphere. Every type of gas has a unique set of spectral-emission lines. The colors of the aurora are determined by the colors emitted by gases in Earth's atmosphere that collide with the solar wind's electrons, affecting magnetic field lines. This effect is similar to a neon light–electrons pass through a gas in a glass tube, causing them to light up.
- Have students look at photographs of auroras. Go to the NOVA aurora image gallery (www.pbs.org/wgbh/nova/magnetic/aurora.html) or the THEMIS aurora image gallery (ds9.ssl.berkeley.edu/themis/gallery_auroras.html) and project the images for the whole class. Ask students to take note of the colors they see and to hypothesize about what is responsible for auroral colors.
- Next, have students view various light sources through a diffraction grating or handheld spectroscope to compare the patterns of emitted light. Also have photos of sample spectra available for students to observe. Arrange various light sources around the room (see examples below). Make the room as dark as possible for optimum viewing.
- incandescent light bulb (students should see a continuous spectrum due to heating of the metal filament)
- gas discharge tubes such as neon, nitrogen, oxygen, or air, (students should see emission-line spectra similar to auroral light)
- fluorescent light bulb (students should see emission-line spectra similar to auroral light)
NOTE: If using diffraction gratings, make sure students hold them by the cardboard edges to avoid smudging the gratings. When viewing light sources through a grating, students should hold the grating several inches in front of their eyes.
- Have students sketch what they see with colored pencils, crayons, or markers and compare how the overall color of the discharge tubes compares with the colors of the individual spectral lines (the overall color is a combination of the spectral lines; for gases that have some very strong lines, the overall color may be dominated by these lines).
Explain to students that what they observe in the discharge tubes and fluorescent light bulbs is similar to the process that produces northern lights. About 200 miles above Earth's surface, solar wind electrons colliding with oxygen atoms produce all-red auroras. At lower altitudes (around 60 miles), oxygen atoms emit yellow-green light. Nitrogen ions, hydrogen, and helium are responsible for the often hard-to-see blue and violet light. Neutral nitrogen produces red and pink colors at lower altitudes. The "dancing" motion of the northern lights is caused by the dynamic interaction between the solar wind and Earth's magnetic field.
Consider impacts of space weather. Space weather is the term used to describe the changing environmental conditions in space caused by activity on the sun. Changing conditions in space weather are responsible for the majestic lights of the aurora and some damaging events on Earth and in space. The geomagnetic storms (disturbances in Earth's magnetic field caused by solar wind gusts) produce the northern lights and trigger potentially harmful effects on humans, animals, and technological systems. During severe space weather events the following can happen:
- people traveling in aircraft (including commercial airliners, the space shuttle, or the International Space Station) can receive high levels of radiation exposure
- telecommunications and GPS satellites are subject to interference, damage, or destruction
- radio communications can be disrupted or blacked out
- disruptions in power grids can cause power outages on the ground
- currents induced in gas and oil pipelines can lead to corrosion or leaks
- migrating animals that use Earth's magnetic field for navigation can be thrown off course
Our society's dependence on technology makes understanding space weather vitally important. The National Oceanographic and Atmospheric Administration (NOAA) has produced three scales to measure and predict space weather conditions and their potential effects on humans and technological systems. Each scale is numbered, much like the scales used to describe the severity of hurricanes, tornadoes, and earthquakes. The Kp index used to characterize geomagnetic storms tells us, on a 9-point scale, how much the solar wind disrupts Earth's magnetic field. The higher the index number, the greater the magnetic activity, with 1 indicating calm weather and 5 or more indicating a geomagnetic storm. Each scale also lists potential impacts associated with levels of storm severity and how often events are likely to happen within an 11-year solar cycle.
Obtain the NOAA Space Weather Scale for Geomagnetic Storms at www.swpc.noaa.gov/NOAAscales/#GeomagneticStorms. Project the table or print and distribute it to each student. As a class, discuss the table, paying attention to the average frequency of severe space weather events per solar cycle. Based on this information, have students discuss the importance of space weather forecasting and why increasing the number of space weather detection instruments (both on the ground and in space) could help protect us from the harmful effects of space weather.
Determine the likelihood of seeing auroras in your area. Using the tables below, have students first determine their approximate magnetic latitude and then the value of the Kp index required for auroras to be visible at their magnetic latitude. Magnetic latitude differs from geographic latitude because it is measured relative to the orientation of Earth's magnetic axis rather than Earth's rotational axis.
||Aurora visible at magnetic latitude
Based on the NOAA scales students examined in Before Viewing question 4 (the scales indicate the level of solar storm activity), have them predict how long it might be before they see an aurora near home. To check current measurements of the Kp index, have students follow this link to the Space Weather Prediction Center's FTP server for Kp plots and choose the most current plot: www.swpc.noaa.gov/ftpmenu/plots/kp.html. Students can also visit the NOAA Space Weather Prediction Centers: "Space Weather Now" page (www.swpc.noaa.gov/SWN/) to see the latest image of the sun, the current NOAA scales activity, current solar wind conditions, and the most current auroral map.
Research auroral events of historical significance. People have observed auroras for thousands of years. Major solar and geomagnetic storms have produced spectacular auroral events worthy of extensive news coverage. Have students choose an auroral event of historical significance to research. An archive of aurora-related news stories can be found at: www.solarstorms.org/Scommun.html. From their findings, students should prepare a short report or presentation containing the following information (as available):
- Date of event
- Location(s) of aurora sightings
- Impacts on humans and/or animals
- Images of the aurora
- Space weather information and the instrument(s) that reported measurements
Investigate auroras on other planets. Auroras are not unique to Earth. Any planet or moon with an atmosphere and a significant magnetic field may produce auroras. Over the years, different satellites have taken images of extraterrestrial auroras. Have students find images of auroras on other planets and compare them to satellite images of auroras on Earth. To determine what auroras might look like from the surfaces of other planets, have students research the composition of these planets' atmospheres. Good links for getting started include:
Compare atmospheric weather and space weather.
To some extent, space weather and atmospheric Earth weather are similar. Have students compile lists of similarities and differences, at least three examples for each, between space weather and weather here on Earth. Each list entry should be accompanied by an explanation of how the phenomena are similar and different. The table below describes some major similarities and differences.
- Occurs close to Earth's surface (i.e., the troposphere)
- Describes the specific environmental conditions (e.g., temperature, wind speed, precipitation, etc.) of Earth's atmosphere at a particular place and time
- Wind involves movement of air particles
- Heat from the sun is the primary driver of atmospheric weather
- Occurs far above Earth's surface (i.e., the ionosphere)
- Describes the specific environmental conditions (e.g., solar wind speed, magnetic field direction, etc.) in space caused by activity on the sun
- Solar wind involves movement of charged particles
- Solar (magnetic) activity is the primary driver of space weather
- Both types of weather vary from place to place over time
- Wind/Solar wind speeds vary from light breezes to strong gusts
- Strong wind gusts/storms can cause damage
- Atmospheric and space weather patterns both vary daily, monthly, yearly, over decades, and even longer.
Offers resources related to northern lights, including additional activities, streamed video, and reports by experts.
Teachers' Domain—Gallery of Auroras
Offers an interactive slideshow of auroral images and information about how and where auroras are formed.
Discusses how Earth's magnetic field works and the impact of magnetic fluctuations on animal navigation, and has a timeline of magnetic reversals, a gallery of images.
NCAR High Altitude Observatory and the Comet © Program–Physics of the Aurora: Earth Systems
Explains physical systems and processes in Earth's upper atmosphere and magnetosphere that produce auroras. Information is presented through readings, images, and animations.
THEMIS Education and Public Outreach Site
Presents information for students and the general public about the THEMIS (Time History of Events and Macroscale Interactions During Substorms) mission and the science of exploring auroras.
NASA IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) Activity–A Soda Bottle Magnetometer
Describes how to build and operate a simple magnetometer made from a soda bottle and a bar magnet to monitor changes in Earth's magnetic field.
Ask the Space Scientist About Earth–Magnetic Field
Lists frequently asked questions about Earth's magnetic field, including questions about magnetic field reversal and its effect on humans.
Northern Lights: The Science, Myth, and Wonder of Aurora Borealis
by George Bryson, Calvin Hall, and Daryl Pederson.
Sasquatch Books, 2001.
Discusses legends, myths, and science of the aurora borealis alongside nearly a hundred photographs shot from remote locations in Alaska.
An Introduction to Space Weather
by Mark Moldwin.
Cambridge University Press, 2008.
Explains sun-Earth connections and the impacts of space weather on our technological society.
Storms in Space
by John W. Freeman.
Cambridge University Press, 2001.
Discusses hazards of space weather, the state of the art in space weather forecasting, and models used to predict space weather and how such models might be improved.
Secrets of the Aurora Borealis (Alaska Geographic)
by Syun-Ichi Akasofu. Alaska Geographic Society, 2003.
Presents basic facts about the aurora borealis and how it has been perceived throughout history.
Erin Bardar is a curriculum developer in Cambridge, MA. She has a bachelor's degree in Physics from Brown University and a doctorate in Astronomy from Boston University. In addition to writing physics, astronomy, and Earth science curriculum for a number of projects, Erin also created the Light and Spectroscopy Concept Inventory for evaluating college astronomy students' understanding of light and spectroscopy, and she has a U.S. patent for a binocular spectrometer.