SOLAR OBSERVATIONS IN THE SECONDARY CLASSROOM
ERIC CONWAY
SYKESVILLE MIDDLE SCHOOL
7301 Springfield Ave
Sykesville, Maryland 21784
econway@umd5.umd.edu
[Jacob Burkhart observes the sun with a 4.5 inch Newtonian Reflector and
a .003% transmitting solar filter at Sykesville Middle School in Sykesville,
Maryland]
©1992 E. Conway. This paper was written as a course requirement
for the Maryland Spacegrant Consortium's Space Science Internship Program.
It may be used for educational purposes and may be distributed providing
this message and the author's name remains. It may not be duplicated or
reproduced by any means for commercial use.
******Special thanks to Jacob and Linda Burkhart for providing
the pictures used in this page!
CONTENTS
RELATED LINKS
INTRODUCTION
With fewer students choosing scientific careers and today being a time in
which scientific literacy in our country has diminished, it is increasingly
important to present science to our students as a rewarding process of exploration,
observation, and discovery. To do this, we must model the true nature of
science for our students and involve them in real, relevant scientific investigations
based on the work of actual scientists. Astronomy is a topic that, if taught
well, can model this aspect of science and motivate students to participate
in scientific adventures on their own. Students have an inherent interest
in the cosmos and they often discover that a direct observation of a heavenly
body is a fascinating endeavor which can lead to an increased interest in
and awareness of the world around them.
The problem that exists with teaching astronomy as an observational process
is obvious; during the school day most typical observations are impossible
and nighttime observation is often very difficult to organize. There is,
however, one object that can be observed and studied on a regular basis.
This of course is our own star, the sun. A detailed program of solar observations
is easy to organize and it will provide the students with a direct experience
with a real scientific investigation while the students learn scientific
principles.
Contents
BASIC SOLAR PHYSICS
Our sun is very similar to most of the stars that exist in the universe.
The one quality that sets it apart from other stars is its proximity to
earth, making it easy to observe and study on a regular basis. From this
study, we can learn a great deal about other stars in the universe as well
as determine how our star influences and drives the processes that exist
on earth. Although scientists have been systematically studying the sun
for the past century, very little is actually known about the sun and how
it works. One area of solar study that is fairly well understood, however,
is the surface activity that occurs on the sun.
Through mechanisms not yet fully understood, the sun generates intense magnetic
fields deep in its interior. Hot streams of electrically charged particles
move upward to the solar surface as cooler gasses move inward to fuel the
sun's nuclear fires in the core. It also known that the sun is a rotating
ball of gasses and at the equatorial regions the rotation is faster, with
a period of about 25 days, while at the poles one rotation can take as long
as 36 days (1). This difference in rotation is thought to cause the sun's
magnetic lines to become kinked and warped. These turbulent conditions are
thought to somehow create the sun's magnetic fields, although there is no
consensus as to how these mechanisms actually are carried out (2).
These magnetic regions tend to erupt through the surface layer of the sun,
known as the photosphere, and create areas characterized by regions of intense
and concentrated magnetic activity. Known as active regions, these areas
are known to be associated with a variety of solar phenomena. Sunspots are
the most widely recognized features associated with active regions. As an
active region grows in size, sunspots begin to appear individually or in
groups. Sunspots appear darker than their surrounding areas because the
intense magnetic field that passes through a sunspot prevents heat from
traveling through that part of the photospheric gasses. Because of this,
sunspots are cooler regions in relation to the rest of the sun's surface.
A sunspot is usually around 4000 C compared to its surrounding area which
is 6000 C (3).
[Closeup of a sunspot group]
Also associated with active regions are coronal loops and arches. Coronal
loops are found above the photosphere and they connect regions of opposite
magnetic polarity while coronal arches are much larger and they are usually
found connecting two different active regions. These features appear bright
because energy flowing along the magnetic lines heats gasses in the sun's
atmosphere, causing them to glow (4).
A solar prominence is a small, short-lived spray of gasses that forms at
the junction between different polarities in an active region. Prominences
are usually found in strong, young active regions that have large sunspots
in them. These features can rise a considerable distance above the sun's
surface and release quite a bit of energy into the sun's outer corona (5).
When this occurs, coronal streamers often appear. Usually visible only during
a solar eclipse, the visible portion of a coronal streamer extends several
times the sun's radius out from the photosphere. The footpoints of the streamer
are in the regions of opposite magnetic polarity, thus the streamer straddles
the prominence. The lower portion of a streamer consists of a magnetic field
that loops from one polarity to the other, however, higher up, the magnetic
field is drawn out into interplanetary space. Gasses and particles flowing
out along these open magnetic fields help create the solar wind (6). The
solar wind is an outflowing of charged particles that travels at a speed
of over 1 million miles an hour. The solar wind caries with it magnetic
fields from the corona, exposing the Earth and anything else in its path
to the influence of the sun's magnetic fields (7).
Occasionally an active region explodes with an intense release of magnetic
energy called a solar flare. This causes sudden large increases of radiation,
especially in the x-ray spectrum, and expells huge quantities of energetic,
high speed particles into space (8). As these x-rays and high speed particles
are ejected from the sun, they travel towards earth. As they reach earth,
the particles from a flare slam into the Earth's magnetic field, squeezing
and strengthening it while accelerating immense numbers of electrons toward
the poles. As these electrons descend into the Earth's upper atmosphere,
they collide with nitrogen and oxygen molecules, exciting them and causing
them to glow. This effect produces brilliant auroral displays, also known
as the northern and southern lights (9). The resulting geomagnetic storms
can also disrupt communication systems on earth, damage sensitive satellites,
cause geomagnetic surveying equipment to go haywire, and induce destructive
current surges in transformers and transmission lines causing power failures
over large areas (10).
Contents
THE SOLAR CYCLE AND ITS EFFECTS ON EARTH
Galileo is usually given credit for being the "discoverer" of
sunspots when he turned his telescope toward the sun in 1610 and observed
sunspots through the haze of a cloudy day (11). Although it was not known
what caused sunspots, it became known that the activity on the surface of
the sun was not constant and that at different times different amounts of
solar activity could be directly observed. A couple hundred years later,
in 1843, a German amateur astronomer named Heinrich Schwabe determined that
the number of sunspots rose and fell in a regular cycle (12). By continuing
Schwabe's observations, and researching historical records, astronomers
have charted the sunspot cycle through 21 repetitions and it has been found
that the sunspot cycle is not as regular as it first appeared and that its
period varies between 9 and 13 years between maximum, with an average period
of 11.2 years (13). The solar cycle also appears to operate on longer term
cycle, with the length of the cycle fluctuating on a cycle that seems to
follow an 80 or 90 year period (14).
During years of maximum or near maximum solar activity, the number of sunspots
increases, solar flares increase in number, and the solar wind intensifies.
Large numbers of sunspots appear at the equatorial region of the sun during
the maximum and they migrate toward the poles as the cycle moves toward
its minimum (15). The magnetic polarity of the sun also reverses about the
same time as a solar maximum occurs, which has led many scientists to describe
a 22 year solar cycle based on the shifting polarity of the sun (16). For
most purposes, though, the 11 year cycle is used to describe solar activity.
At the solar minimum the sun is much less active, fewer sunspots appear,
and solar wind and flares are not as prominent.
[graph of the solar cycle]
Almost as soon as it was discovered that there was a cycle of solar activity
that followed a regular pattern, researchers tried to find relationships
between terrestrial phenomena on earth and the solar cycle. It is well known
that aurora activity increases with increases in solar activity due to increased
solar flares, but little else has been successfully linked with the solar
cycle. The sunspot cycle has been linked to all sorts of terrestrial effects
including soil temperatures, monsoon patterns, salmon catches, influenza
outbreaks, and admissions to psychiatric hospitals (17). All of these correlations,
however, have broken down when faced with the test of time.
Perhaps the most sought-after relationship between the sunspot cycle and
Earth is the possibility of a sunspot-weather correlation. Scientists have
tried to match the sunspot cycle to long range weather conditions on Earth,
however they have had little success. A long line of proposed theories has
appeared and none of them has survived the test of time. It does appear,
however, that a correlation exists between droughts and minimum solar activity.
Several major droughts in the late 1800's and early 1900's have occurred
during years of sunspot minimum activity, however, there is no explanation
for why this occurs or if there is a direct link to sunspot activity and
drought (18). In 1989, a theory that has some promise surfaced that linked
sunspot activity with upper atmospheric winds in the polar regions. These
polar stratospheric winds shift direction with a period of shifting that
is between 1 and 1.5 years. This study found that in years during which
polar winds blow from the west, the polar temperatures rise and fall with
the sunspot cycle. When winds in the polar atmosphere blow from the east,
polar temperatures do the opposite of what the sun is doing. The theory
then states that the fluctuations in the upper atmosphere in the polar regions
has a direct influence on global weather systems. The mechanism behind this
correlation is unknown and further study is necessary to determine if this
is a true relationship or a coincidence (19). A second theory, proposed
in 1989, states that changes in climate follow the 22 year solar magnetic
cycle. These researchers found that air temperatures taken at night above
the oceans fluctuate with a 21.8 year cycle that correlates in step with
the 22 year magnetic cycle. They found that alternate peaks in the 11 year
sunspot cycle match with alternate upward or downward changes in these air
temperatures. The temperature fluctuations are only a couple of tenths of
a degree celsius, however this small change could effect global weather
in discreet ways (20). In the most recent theory, proposed in 1991, researchers
found that the length of the solar cycle in related to average temperatures
on earth. It was found that when the sunspot cycle is longer that usual,
the sun is least active and temperatures on earth drop. Their correlation
holds steady from the mid-1800's to the present, thus adding to the reliability
of the correlation (21).
If a true sunspot-weather link could be found, the benefits for long range
weather forecasting would be immense. Predictions could be made that could
help people prepare well in advance for storms, droughts, or fluctuating
temperatures. The problem that exists with these theories is a lack of reliable
data over a long time period, a lack of understanding of the true mechanisms
that control solar activity and our atmospheric processes, and the altering
of our atmosphere caused by man. It is possible that any solar-terrestrial
climate relationships will be covered up by man-made changes in our atmosphere,
leaving scientists only guessing about this relationship.
Contents
CLASSROOM OBSERVATION OF THE SUN
Whenever discussing solar observations with students, it is imperative that
all people involved, including teachers and students, understand that looking
directly at the sun, especially through any type of magnification device
or improper filter, will result in serious eye damage. Even if the observation
is only a second or two, an improper look at the sun will result in damaged
eyesight or even blindness. Measures can be taken, however, that allow observers
to view the sun and discover features of the sun that can prove to be fascinating
to study.
Solar images can be collected in a variety of ways. The two easiest and
most common methods of solar observation are direct observation using solar
filters and image projection onto a screen using a variety of light gathering
instruments such as binoculars or telescopes (22). Expensive equipment is
not necessary, a pair of 7x35 binoculars or a small 10x finder telescope
will provide your students with great projected solar images.
Solar observations also will be best during the morning hours before the
ground has had a chance to heat up and produce turbulence that will ruin
your viewing (23).
Direct observations using filters
The observations that will reveal the most detail of the surface of the
sun are those that utilize solar filters and allow for direct observation
of the sun. Two types of solar filters exist, filters that are placed on
the eyepiece of a telescope and filters that are placed on the aperture
(opening) of a telescope. Eyepiece filters are not recommended since they
can be extremely dangerous. These filters are not designed for different
sized telescopes and they do not offer protection with any telescope larger
than a 2 inch refractor. Even with a 2 inch refractor they are only safe
when used for short 30 second observations (24).
[aperture type solar filter]
Filters that are used on the aperture end of the telescope are the safest
type to use since they reflect or absorb most of the solar radiation before
it enters the scope. This also protects the telescope from excessive heating
which will ruin both your viewing and, possibly, your telescope (25). No
substitutions should be used. Often observers will substitute fogged film
or developed photographic film as a solar filter, but neither of these techniques
is safe since these makeshift filters still allow ultraviolet and infrared
radiation to pass through (26).
Direct viewing can offer the observer an excellent view of the surface of
the sun and its sunspots. A telescope with an aperture of 6 inches with
a proper filter will allow a student to observe the granulation of the photosphere
in some detail along with other surface characteristics of the sun (27).
This size telescope is often hard to come by since larger telescopes are
expensive and fragile, however, a smaller telescope will offer a decent
view of the sun's surface. Another problem with this type of observation
is that it is difficult to get an entire class to observe the sun at one
time with this method. This is why solar image projection may be the better
alternative for solar studies in the classroom.
Image projection
Image projecting is the easiest method of solar observation when in a classroom
situation since it allows many people to view the image at the same time
(28). It is also the easiest and most accurate way to observe and record
the position of sunspots on the sun. The equipment needed for this activity
is a telescope of any size or a pair of good binoculars. The best telescope
set-up would be a refractor on an equitorial mount tripod. Reflectors will
work, however the heating effects of a reflector can ruin the "seeing"
of the telescope (29).
The projection apparatus can be set up in a variety of ways depending on
the equipment you are using, but most projection systems require a fixed
projection screen behind the eyepiece of the telescope, the telescope, and
a shade card to prevent unwanted sunlight from washing out the solar image
(30). If using binoculars, block or cover one of the lenses and set up the
apparatus in the same manner as you would a telescope.
[Herman Hyne of Baltimore, Maryland demonstrates solar projection with a
telescope]
To project a solar image, the telescope is aimed at the sun. Adjust the
position of the telescope so that its shadow is as small as it can possibly
get. At this point, finely adjust the telescope's position until a solar
image is projected onto the projection screen. Use the telescope's focus
knob to sharpen the image as much as possible.
Drawing sunspot images
As the image is projected on the projection screen, sunspots appear as dark
spots on the solar disk. Often it is desirable to record the position of
various sunspots and sunspot groups. A piece of clean white paper with a
6 inch circle crossed with a fine grid can be attached to your board (the
circle's size will depend on the size of your telescope, 6 inches corresponds
to a 3 inch refractor with a 3/4 inch eyepiece). The circle and the grid
are placed on the projection screen and the solar image is projected over
the grid (31).
This grid can be used to identify and record the position of sunspots, but
first the grid must be oriented. Before making a drawing, leave the telescope
stationary for a minute or two and let the image drift across the screen,
twisting the grid until a sunspot trails along one of the East-West lines
on your grid. The image will move from right to left due to the Earth's
rotation, with the west limb of the sun preceding (leading) and the east
limb of the sun following (32). Once oriented, a drawing of the sunspot
positions can be made and saved for future use. Sunspot groups should be
recorded as groups and individual spots should be identified as individuals.
[data sheet for solar observing]
If your image is sharp enough, a fuzzy, lighter area around each sunspot
may be visible (direct filtered viewing of the sun will usually allow this).
This is the penumbra of the sunspot while the umbra is the darker, sharper
part of the spot. If the penumbra and umbra are visible, it is possible
to have your students classify each sunspot based on the McIntosh system
of sunspot group classification. This system classifies sunspots based on
the presence of penumbra, the symmetry of the largest spot's penumbra, and
the sunspot distribution within a group (33). The students can identify
each sunspot or group of sunspots and label this on their drawings.
Counting sunspots
Scientists keep track of the daily number of sunspots to keep track of solar
activity over time. The daily sunspot number, known as R, is calculated
daily using observations taken from around the would using the observed
number of sunspot groups, g, and the total number of individual spots, s,
with the equation:
R = 10g + s. (33)
Using this equation, the number of groups is weighted ten times heavier
than that of individual spots to account for the greater magnetic field
present in a sunspot group, thus R is actually a measure of the total magnetic
field present in the sunspots each day (34). Using this technique, students
can calculate R and compare their values with the actual values. Their value
of R can also be recorded on the student's sunspot drawings.
Using historical records, a simple line graph of the yearly average of R
versus time will illustrate the sunspot cycle and the average length of
each cycle can be calculated with this data.
Contents
CONCLUSIONS
Using the techniques of solar observation mentioned in this paper, it is
possible to set up a daily program of solar observation that could last
for several weeks, if not the entire year. Once the students are used to
making their observations, it will only take a couple minutes each class
period to record their solar observations. Students could become expert
solar observers and actually submit their information to any groups that
monitor solar activity on a daily basis. These activities could be further
extended with research activities, science fair projects, computer programs,
newsletters, and student peer teaching activities. Throughout this activity,
the students will be participating in a scientific investigation that has
a real purpose and is exciting. From this, the students will learn that
science is not just books and tests, instead it is a challenging, rewarding,
and fun process in which new things are constantly being discovered.
Contents
FOOTNOTES
1. Bartusiak, Marcia (1989). "The sunspot syndrome." Discover,
10: pg. 50.
2. Bartusiak, pg. 47.
3. Bruning, David (1992). "One day on the sun." Astronomy, 20:
pg. 51.
4. Bruning, pg. 50.
5. Bruning, pg. 50.
6. Bruning, pg. 51.
7. NASA, Solar Physics in the Space Age, pg. 22.
8. Bruning, pg. 51.
9. Bartusiak, pg. 46.
10. Bartusiak, pg. 46.
11. Hromoco, J. (1989). Weather or Not. National Air and Space Museum, Smithsonian
Institute, Washington, DC, pg. 7.
12. Muriden, J. (1983). Amateur Astronomer's Handbook: A Guide to Exploring
the Heavens. Harper and Row, New York, pg. 125.
13. Newall, N. (1989). "Climate follows double sunspot cycle."
New Scientist, 123: pg.27.
14. Gribbin, J. (1991). "Climate change - the solar connection."
New Scientist, 132: pg. 22.
15. Bartusiak, pg. 49.
16. Bruning, pg. 51.
17. Bartusiak, pg. 48.
18. Hromoco, pg. 7.
19. Loon, H.V. and Labitzke, K. (1988). "When the wind blows."
New Scientist, 119: pg. 58.
20. Newall, pg. 27.
21. Gribbin, pg. 22.
22. Muirden, pg. 122.
23. Muirden, pg. 123.
24. Muirden, pg. 122.
25. Levy, D.H. (1991). The Sky: A User's Guide. Cambridge University Press,
New York, pg. 89.
26. Levy, pg. 89.
27. Levy, pg. 90.
28. Tattersfield, D. (1979). Projects and Demonstrations in Astronomy. John
Wiley and Sons, New York, pg 100.
29. Mims, F.M. (1990). "The amateur scientist: Sunspots and how to
observe them safely." Scientific American, 262: pg. 130.
30. Mims, pg. 130.
31. Muirden, pg. 124.
32. Muirden, pg. 125.
33. Levy, pg. 91.
34. Levy, pg. 91.
Contents
LITERATURE CITED
Bartusiak, M. (1989) "The sunspot syndrome." Discover, 10:45-52.
Bruning, D. (1992) One day on the sun." Astronomy, 20:49-54.
Gribben, J. (1991) "Climate change- the solar connection." New
Scientist, 123:22.
Hromoco, J. (1989) Weather or Not? National Air and Space Museum, Smithsonian
Institute, Washington DC.
Levy, D.H. (1991) The Sky: A Users Guide. Cambridge University Press, New
York, pp. 87-96.
Loon, H.V. & Labitzke, K. (1988) "When the wind blows." New
Scientist, 119:58-60.
Mims, F.M. (1991) "The amateur scientist: Sunspots and how to observe
them safely." Scientific American, 262:130-133.
Muirden, J. (1983) Amateur Astronomer's Handbook: A Guide to Exploring the
Heavens. Harper and Row, New York, pp 121-137.
NASA Publication (NP-106): Solar Physics in the Space Age. pp.22,45-46.
Newall, N. (1989) "Climate follows double sunspot cycle." New
Scientist, 123:27.
Tattersfield, D. (1979) Projects and Demonstrations in Astronomy. John Wiley
and Sons, New York, pp. 99-104.
Contents
Copies of this document can be found at the Maryland Spacegrant
Consortium - Space Science Internship Program Home Page
http://msx4.pha.jhu.edu
This Page was created June 22, 1996 for the Maryland Space
Grant Consortium/Space Science Internship Program. If you have any questions/comments
specifically about this page you may contact the author at econway@umd5.umd.edu.
Please direct any questions regarding the program to the Maryland Spacegrant
Consortium office. Thank You.