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 This
newsletter is a joint project of SIRS Publishing,
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SEPTEMBER 1993 — VOLUME 1, NO. 1
ARTICLES
It's no wonder ancient peoples (and some modern ones) have worshiped the sun. Without It's life-giving warmth, the earth's creatures would die. Our daily moods and activities are also tied to sunshine and the seasons. But how much do we really know about our backyard star? Test your knowledge with this short True/False quiz. You may be surprised by the facts about the sun.
1. The sun is about 50 times bigger than the earth.
2. The distance between the sun and the earth is constant.
3. The sun's invisible outer atmosphere is cooler than its surface.
4. The surface of the sun is much hotter than a lightning bolt.
5. Sunspots are cooler than the rest of the solar surface.
6. The sun's equator rotates faster than its poles.
7. The sun is about halfway through its predicted life span.
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1. False: The diameter of the sun is 1,393,000 kilometers
(865,000 miles). That's long enough to fit 109 earths straight across the middle
of the sun.
2. False: The sun is actually about 3 million miles closer
to the earth in January than it is in July. The average distance from the center
of the sun to the center of the earth is 93 million miles.
3. and 4. False: The core of the sun is about 27 million degrees
Fahrenheit. The temperature decreases steadily outward until at the surface
it is only about 10,000 degrees F. In the corona, or outer atmosphere, which
is usually invisible and extends millions of miles into space, the atoms become
so active that the temperature jumps again to about a million degrees. The center
of the earth is estimated to be about the same temperature as the solar surface,
while a lightning bolt the width of your thumb is five times hotter.
5. True: Sunspots are darker and cooler than the rest of the
solar surface. Scientists were surprised, however, to find out that the sun
gives off the most light when there are the most sunspots. This extra light
comes from extremely bright regions surrounding the spots.
6. True: The equator of the sun rotates about once every 27
days, but the poles take 9 days longer for each rotation. This is possible because
the sun is gaseous, not solid, like earth.
7. False: Scientists estimate that our sun is about five billion
years old and has a life span of another ten billion years or so.
The sun we see warms us on a chilly day, tans well-oiled tourists aid of a natural eclipse. On sandy beaches, gives us the light of day, and appears unchanging to the naked eye as it hovers in the sky like a glowing orb. But this seemingly unchanging star which acts as a life-giving catalyst for earth is a variable sun. The surface seethes and boils at a temperature of 10,000 degrees Fahrenheit. Gas streamers burst from the sun's surface, arching gracefully outward to the superheated atmosphere, only to be pulled back by powerful magnetic forces. Violent solar flares erupt near dark sunspots, sending out invisible streamers of solar particles called the solar wind.
Even though solar reactions occur more than 90 million miles away from earth, their energy affects us. The solar winds that stream outward shower earth's protective magnetic field. This rain of charged particles disrupts radio communications, satellite transmissions, and sends satellites into decaying orbits, causing some to burn up in the atmosphere earlier than intended by the people who launched them. The magnetic interaction also generates brilliant light shows near the magnetic poles. These are known as the aurora borealis (northern lights) and aurora australis (southern lights). Solar explosions of immense proportions also generate high-energy cosmic ray particles that penetrate earth's atmosphere and cause chemical reactions. Dark spots called sunspots mar the surface of the glowing disk, indicating magnetic fluctuations on the sun's surface. These effects and the reactions that cause them fascinate observers and have led to extensive research of our sun's variability and how its changes affect our atmosphere and climate.
The High Altitude Observatory (HAO) was founded high atop the Continental Divide in Climax, Colorado, to study the fluctuating moods of our backyard star. Later HAO became part of the National Center for Atmospheric Research in Boulder, Colorado. The goal of HAO scientists is to understand the sun and its impacts on the earth system by studying the physical processes that govern it. Through such understanding, scientists hope to predict solar activity. Their research poses questions and seeks answers about three areas of solar variability: what causes changes in the light we see, what factors increase or decrease cosmic ray bombardment, and what processes affect levels of ultraviolet radiation. By observing the solar corona, the sun's interior, and solar interactions with earth's atmosphere, scientists try to determine the causes of such variability.
The corona, a halo of gases superheated to more than one million degrees Fahrenheit, extends irregularly outward millions of miles from the sun's surface. Despite its size and high temperature, the corona appears a million times fainter than the sun's surface, or photosphere. This faintness makes it difficult to see without special technology or the aid of a natural eclipse.
A solar eclipse occurs when the moon passes between the earth and the sun. Even though the moon is much smaller than the sun, the distance is so great between them that their sizes appear to be the same. Because natural eclipses do not occur often enough for scientists to fully study the corona, scientists create their own eclipse with a coronagraph.
The coronagraph is a telescope fitted with a dark disk which covers the image of the sun. As the disk dims the sun's brilliance, the corona appears. The first person to use the coronagraph in the Western Hemisphere was HAO founder Walter Orr Roberts, who photographed the corona in the l940s. His discovery that strong flares were followed by radio fadeouts several days later aided Allied forces during World War II who depended on reliable radio communication.
By 1960 Roberts began to forge links between solar studies and atmospheric science. With a consortium of universities he founded the National Center for Atmospheric Research; HAO is just one of four scientific divisions at NCAR that studies some aspect of the earth's atmosphere. Dr. Roberts once said: "No field of science offers a greater potential for the good of all mankind. The sky is quite literally the limit."
Today, the satellites that study the sun approach that lofty limit, flown to their orbits by the space shuttle or rockets and outfitted with special cameras. Photographs and data collected from space are not obscured by the earth's atmosphere, and thus offer scientists a clear view of the sun. The Spartan Mission launched in April 1993 is now training its telescopic eye on the corona. Another effort now orbiting earth on the Upper Atmosphere Research Satellite is the SOLSTICE (Solar Stellar Irradiance Comparison Experiment) device, which compares the energy output of our sun with other observable stars in the universe.
The Solar Maximum Mission launched in the early 1980s captured 250,000 images of the sun's corona during its nine-year orbit, but fell to earth early, a victim of the solar phenomenon it was designed to observe. The satellite fell earthward because as solar activity increases, so does the sun's output of ultraviolet radiation, which causes heat. As earth's atmosphere heats up, the atmosphere expands, creating resistance for objects flying through it. As Solar Max slowed from increasing resistance, it fell. Despite its early demise, scientists extended their knowledge of the sun's gaseous halo.
The corona's common features are illustrated in the above photograph of the solar eclipse in Bolivia. The brightest parts of the corona occur in mounds with a thin spike extending outward above them called coronal helmet streamers. The dimmest parts are referred to as coronal holes. The pattern of coronal helmet streamers and holes changes systematically through the 11- year solar activity cycle. At times of high activity, when many sunspots are visible, streamers and holes appear almost randomly in the corona. At times of low activity, when fewer sunspots are visible, there are large holes in the polar regions of the sun and bright helmet streamers near the equator. Intense heat forces the corona to expand outward with increasing speed to form the solar wind, which fills all of interplanetary space with the corona's ionized gas and magnetic field. The wind expands outward at a speed of about one million miles per hour. Scientists theorize that the solar wind flows well beyond our own solar system, but that its speed drops significantly as it moves outward.
But what engine drives the sun? Although the sun contains every element found on earth, hydrogen and helium gases are the primary elements. Deep beneath the sun's surface tremendous pressure and heat cause nuclear fusion to occur. The nuclei of hydrogen atoms, which comprise most of the sun's makeup, smash into each other so hard that they join together, or fuse, creating helium. This transformation generates huge amounts of energy because four hydrogen atoms have more mass than one helium atom. Albert Einstein determined that such leftover mass multiplied by the speed of light squared equals the amount of energy generated (E=mc2). The energy travels from the sun's 27million-degree core to a radiation zone of dense gases and then to a convection zone of rising circular currents. After a journey that can span thousands of human lifetimes, the energy is released as light in the photosphere, which arrives at earth eight minutes later. Some of that energy generates the layer called the chromosphere and then shoots outward into the corona.
Scientists studying these internal workings of the sun discovered that our star resonates, creating acoustic waves as it seethes. Our gaseous star pulsates, expanding and contracting like a breathing giant. These pulses, which occur unevenly across the surface, start waves moving through the sun's interior. Millions of waves can be moving through the sphere at any one time. Scientists observe these waves by examining Doppler shifts of atomic absorption lines which are displaced towards the red or blue colors of the spectrum. Red shifts indicate motion inward, or away from the instrument, while blue shifts arise from motion outward, or toward the instrument. The Doppler effect is easily illustrated with sound: Stand on the side of a road and listen to the difference between a car moving toward you, and the same one moving away. The pitch will change from high to low as the car moves by you. Instruments that measure the Doppler effect on the sun detect the uneven expansions and contractions produced by the acoustic waves By examining acoustic waves, scientists hope to learn more about the sun's interior. Seismologists study similar waves on earth during and after earthquakes. When sections of the earth move, they generate pressure waves, or acoustic waves, that travel through the planet. By recording the time it takes for a wave to leave an earthquake's epicenter, or origin point, to an established test site, scientists determine the physical workings of the planet's interior. Similarly, helioseismologists examine solar waves to determine what lies below the boiling surface of the sun. Scientists hope that when they discover the sun's interior processes, they will understand what causes variability.
As researchers study this vast engine, they learn more about how the earth's upper atmosphere relays solar changes down to the planet surface. Researchers want to understand how these changes affect our climate. Such has been HAO's goal from its earliest days when Walt Roberts was its lone scientist, high atop the mountains of Colorado. He said, "It's wonderful to have the opportunity given us by society to do basic research, but in return, we have a very important moral responsibility to apply that research to benefiting humanity."
Caroline Hanson
Stuart Reller of Indianapolis, Indiana:
As a youngster, I knew that Uncle Walter was an important scientist, particularly
after we purchased a set of encyclopedias and found his picture included in
the section on astronomy. Certainly anyone with his picture in the encyclopedia
filled me with an instant respect, as well as something for fourth grade show-and-tell.
Despite a certain amount of trepidation, I wrote to Uncle Walter in the hopes that he could provide an explanation of what happened to meteorites as they entered the Earth's atmosphere. I received a letter back from him, I believe in less than a week, and was relieved to find that there were no long equations, complicated diagrams, or tedious scientific explanations that would make my school project even more difficult to complete.
I do not remember his exact words, but I remember how clear and straightforward his explanation was for a ten-year-old. He said a (falling) meteorite is like (a person) trying to run through a swimming pool-the faster you go, the harder it gets, and pretty soon the hard meteorite rock simply melts, with the air being like water and the rock like an ice cube.
I am sure that this is only one of, shall we say, billions and billions of wonderfully straightforward observations and explanations that Uncle Walter made over his lifetime of the phenomena that comprise our universe.
Excerpted from the book Remembering Walt Roberts published by UCAR.
ACTIVITY
To observe marly of the sun's surface changes requires special equipment housed in observatories or launched on satellites, but you and your students can observe the movement of sunspots across the surface of the sun with a minimum of equipment. You will need some packing boxes or appliance boxes, large paper, pencils/pens, a thumbtack or pin, an index card, a small mirror, and some steady hands and observant eyes.
Teachers, please stress to your students the importance of not looking directly at the sun. Any direct viewing can cause permanent, irreversible eye damage. Be sure to monitor student use of the equipment to provide a safe and educational experience. You should also take some time and practice the following activity before presenting it to students.
Procedure: Take students outdoors to an area where the sun is visible. This activity will work best if students work in groups of 3-4 individuals. Have students poke a hole into their index cards using a pin or tack. They should keep the hole as small as possible. One student should stand with his back to the sun and hold up the card so that an image of the star shines through the pinhole onto the ground or someone's hand. At that point another student should use the mirror to reflect the image into a horizontal direction. A third student should then open up one end of the team's box and tape a piece of white paper to the bottom. Holding the box horizontally, the team needs to adjust their position until an image of the sun gets reflected from the mirror onto the paper inside the box. (Fixing the mirror in place works best.) An image of the sun about the size of an adult hand will be projected onto the paper. Sunspots are the darker shadows within the outline of the sun as it shows up on the paper. The darker the interior of the box and the brighter the white paper, the more visible the spots.
Project the image over several weeks and mark the progression of the spots. Because the sun is made of gas, it does not rotate uniformly like earth. Some spots will move more quickly than others depending on their location on the solar sphere. The sun rotates completely about every 27 days. On earth, a single rotation takes approximately 24 hours.
Students who want to track sunspots by drawing them can take a pen or pencil and trace the outline of the sun and the spots. They can change the paper each time they look, or leave the same paper in the box and chart the changes.
You can have your students research sunspots and determine what point of the 11-year sunspot cycle they are viewing.
Note: Student use of mirrors should be monitored at all times to prevent mishaps.
Do You Want to Learn More?
The National Center For Atmospheric Research wants to enrich your classroom resources by offering material on the following:
* What it's like to be a solar physicist
* How you can measure the circumference of the earth using the sun
* How you can observe a magnetic field
* How you can demonstrate sound waves and the effect they can have on a surface
Just send your name, address and indicate which activities you want to know more about to Caroline Hanson, Project LEARN, NCAR, P.O. Box 3000, Boulder, CO 80307.
RESOURCES
National Center for Atmospheric Research 1993 Audiovisuals Catalog,
NCAR Education and Outreach, P.O. Box 3000, Boulder, CO, 80307. Slides, videos,
and photographs of solar phenomenon. Fact sheets and current articles about
solar and atmospheric research are also available.
Exploring the Solar System. National Geographic Society, 1989, Washington, D.C. A good general introduction to the solar system for middle school and younger children.
Sun and Earth, Herbert Friedman, Scientific American Books, 1986, New York. An excellent resource book about the sun-earth system and solar physics.
Information on this subject and others can be found in SIRS Science, a series of volumes on five major topics -- Earth, Physical, Life, Applied and Medical. Each volume contains 70 articles reproduced in their entirety and indexed.
All articles are also included in full-text on SIRS Researcher CD-ROM, which contains thousands of articles related to social issues, science, global events and issues of a historic, economic or political note.
For information write to SIRS, P.O. Box 2348, Boca Raton, FL 33427, or call SIRS Customer Service at 1-800-232-SIRS, or via e-mail at custserve@sirs.com.
Science
Now
is jointly published by the Walter
Orr Roberts Institute at the University
Corporation for Atmospheric Research
and SIRS Publishing, Inc.
(Social Issues Resources Series.) Science
Now is published three times during the
school year and is distributed to SIRS subscribers.
Comments and questions should be directed
to Joyce Gellhorn via Internet at jgellhorn@sprynet.com.
You can also contact your SIRS representative
or write to:
SIRS Publishing, Inc.
P.O. Box 272348
Boca Raton, FL 33427-2348
http://www.sirs.com
Editor:
Caroline Hanson
Scientific
Editor:
Pat Kennedy
Contributors:
NCAR Outreach and Information Staff;
Tom Holzer, Director of High Altitude Observatory,
Tom Bogdan, Dan Gablehouse, HAO scientists
UCAR is a consortium of over 60 universities in the U.S. and Canada with doctoral programs in atmospheric and related sciences. UCAR manages and operates the National Center for Atmospheric Research under the sponsorship of the National Science Foundation. Any opinions, findings and conclusions or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. Anyone who undertakes any of the activities described herein shall do so at their own risk; UCAR and SIRS Publishing, Inc. assume no liability, whatsoever, for any injury or harm, which may result therefrom.
© COPYRIGHT 1993 UNIVERSITY CORPORATION FOR ATMOSPHERIC RESEARCH. ALL RIGHTS RESERVED.
Note to Teachers: Permission is hereby granted to copy all or any portion of this publication for distribution to third parties provided such copying and distribution occur for the benefit of research, scientific and educational purposes and for no other purposes including, but not limited to, commercial exploitation purposes. In the event copying occurs or derivative works, as defined under U.S. Copyright Laws, are created, all notices and/or credits recited herein must remain intact on any copies made or derivative works created.