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4A The Universe #3
Increasingly sophisticated technology is used to learn about the universe....
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Sunspots 2: Correlating Sunspots to Active Regions
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Purpose
Students will understand how the development of new technology has increased our knowledge of how the sun works.
Context
Ultimately, the sun is the source of all life on earth, providing
light and warmth to the organisms that inhabit our planet. As a result,
the sun has fascinated humans throughout history-it has been worshipped
as a god, observed as it appears to move across our skies, and studied
for its composition and behavior. Many cultures have built observatories
to monitor the sun and its observable properties. As technology becomes
increasingly sophisticated, we have been able to gather more and more
information about the sun and use this data to infer things about the
star's behavior.
This activity is part of a three-part series of lessons aimed at showing
students how our knowledge of the universe must be inferred through the
use of scientific tools. Specifically, students study sunspots in these
lessons through the use of solar imaging from satellite instruments currently
circling the sun (Yohkoh and SOHO satellites).
In the first lesson of this three-part series, students were introduced
to sunspots and the types of technology and solar imaging used to visualize
them on the sun's surface. This second lesson allows students to see how
sophisticated technology can be used to learn about the sun. In this activity,
students apply the use of two types of solar imaging to determine a correlation
between sunspots and active regions on the sun. The sunspots are visualized
through the use of visible light solar imaging whereas the active regions
are visualized utilizing x-ray energy. Students compare the two images
and determine the area of sunspots and active regions using a Java applet.
The information gathered is used to determine the existence of a correlation
between the two types of solar features.
Planning Ahead
Materials:
- Graph paper
- The Exploratorium site contains many images that may require significant
time to view depending on the type of connection available. The approximate
load times for images on this site are listed below for each corresponding
connection type:
|
Connect Rate
|
Connect Time
|
| 14.4K |
44.41 sec. |
| 28.8K |
24.60 sec. |
| 56K |
16.63 sec. |
| ISDN 128K |
6.12 sec. |
| T1 1.44bps |
1.81 sec. |
- In the activity, students compare visible light images to x-ray
images of the sun using a Java applet. To successfully launch the
applet, students will need to use a Java-enabled browser such as Netscape
4.0 and higher or Internet Explorer 5.0 or higher. Downloads to upgrade
browsers can be found at:
Motivation
Ask students:
- What is a correlation? (The degree to which two things
are related to one another and change together.)
- Describe examples where two events are correlated to one another.
(Have students brainstorm events that are correlated to one another
and describe how they are correlated. For example, risk of lung cancer
and smoking are correlated in that the more an individual smokes over
time, the greater his/her risk will be for developing lung cancer.)
- How can we determine whether active regions in the corona and
sunspots are correlated to one another? (This is a brainstorm
question. Students should be given time to review, if necessary, what
sunspots, active regions, and the corona are. Students should also
review that sunspots were seen in visible light images of the sun,
whereas active regions were visualized through x-ray images of the
sun. Students may suggest that to determine a correlation, one should
be able to determine if a sunspot is always in the same place as an
active region. They may also suggest counting the number of sunspots
and active regions and determining a correlation that way.)
Development
Tell students they will compare images taken of the
sun using visible light and X rays. They will graphically determine whether
sunspots seen on the sun using visible light are related to the active
regions seen at the sun's corona using x-ray energy. The images they will
use were taken by the Yohkoh satellite in January of 1992. There are 26
pairs of images, one pair (one visible and one x-ray image) for each day
of January from the 5th to the 30th of the month.
Because there are 26 pairs of images, it is best if the class is divided
into pairs, where each pair does a subset of images. Another option is
to split the class and have each half of the class collect data on all
26 pairs of images. This will allow the class to collect two sets of data,
which can be graphed, analyzed, and compared to one another. Assign images
to students and bring the class to a computer lab.
Tell students that they will use an interactive Java applet to visualize
their assigned images. The applet will allow students to circle the area
around each sunspot and active region using the cursor. The applet will
record the area (in pixels) of the sunspot and active regions outlined
by students. These areas should then be recorded in a table made independently
by the students. The class will then pool together its data and graph
the area of the active regions (x-ray) against the area of sunspots (visible
light) to determine whether or not there is a correlation.
Allow
students time to read page 2 of the online activity at the Exploratorium's
Sunspots
site to introduce them to the activity and the use of the Java applet.
Students should also become familiar with identifying the dark sunspots
in visible light images and the bright, intense active region emissions
that are visible in the x-ray images.
Encourage students to make their own data tables for recording areas of
sunspots and active regions. Their data tables should be long enough to
include information on all 26 dates for the month of January. Data tables
should include the following information:
- Date
- Area of sunspots (pixels)
- Area of active regions (pixels)
- Ratio of x-ray area/sunspot area (There are no units because pixels
cancel each other out.)
Have students collect information for their assigned subset of images
using the Java applet. After all students have collected the information,
pool together data so that each student has areas of sunspots and active
regions for all 26 pairs of images of the sun. If the class was able to
gather two sets of data, have students make another data table for the
second set of data. Have students calculate the ratio of x-ray area to
sunspot area for each pair of images and record the results in their data
tables.
Ask students:
- The ratio of x-ray area/sunspot area measures the correlation
between the two. Do the ratios indicate a correlation between the
two? (This will depend on the students' data. However, students
should note that looking at so many numbers makes it difficult to
ascertain whether or not there is some correlation. Some students
may thus suggest that a visual representation, or graphing, will make
any correlations easier to see and determine.)
- How can we graph the data to determine whether or not there is
a correlation between sunspot area and active region area? (Students
should suggest making line graphs of the x-ray area and the sunspot
area.)
Distribute graph paper to students. Tell students that they will make
three graphs:
- Sunspot area vs. Time
- Active region area vs. Time
- X-ray area vs. Sunspot Area
It is best to have students make these graphs and discuss them in this
specific order. Students will have an easier time understanding the area
vs. time graphs since those graphs will tell them how sunspot or active
region area changed over time. The last graph (x-ray area vs. sunspot
area) does not factor in time and simply examines whether or not there
is a linear correlation between the two. Correlations do not depend on
the passage of time. The absence of a time axis may disorient students
who have not done much graphing. Thus, if your students need to approach
the goal of the research activity more slowly (the existence of a correlation
between sunspot and active region areas), start with plotting the areas
measured on the images against time.
Each graph should have the following features:
- Title
- Clearly labeled axes with units
- Clearly labeled points
Tell students that by making the first two graphs, they will study the
change in sunspot area and active region area over time. For each graph,
the area (sunspot or active region) will be on the vertical or y-axis.
The date (days) will be on the horizontal or x-axis.
The time graphs will have some shape, not necessarily linear or smoothly
curved-they may have sudden jumps as spots and x-ray areas appear and
disappear because of the sun's rotation, or as active areas become brighter
and dimmer. Both the evolution of the sunspots or active regions and the
rotation of the sun (once per 28 days) affect each day's data. For sunspots,
the effect of rotation will likely dominate, as the sunspots evolve on
a time-scale of several weeks or months. X-ray regions may vary on much
shorter time scales.
After students have made their graphs (sunspot area vs. time and active
region area vs. time), ask them:
- How did sunspot area change over time in January 1992? (Have
students analyze their graphs.)
- How did active region area change over time in January 1992?
(Have students analyze their graphs.)
- Does comparison of the two time graphs show any noticeable trends?
Describe. (If the two graphs show a similar overall shape,
comparing them may help students discover the correlation themselves.
The more the shapes are alike, the closer the correlation graph would
be to a straight line. Remember that the vertical scales of the two
time graphs are different, so that a similarity indicates the x-ray
and sunspot areas are proportional, not identical. Encourage students
to make guesses about what the x-ray vs. sunspot graph will look like.)
After making the first two graphs (sunspot area vs. time and active region
area vs. time), have students make a graph of sunspot area vs. active
region area. Sunspot area (pixels) will be on the horizontal or x-axis
and active region area (pixels) will on the vertical or y-axis. Students
should match each day's sunspot area from the visible light image with
the corresponding day's active region area from the x-ray image. The points
will not be ordered in time because time is not one of the axes on the
graph.
Sample graphs for sunspot area vs. time and active region area vs. time
can be found at the Science
Education Gateway site in the Graphing Sheets section.
Students' data should yield a linear relationship between area of sunspots
and area of active regions. If the data do yield a linear relationship,
have students calculate the slope of the line (ratio of x-ray area/sunspot
area). However, if a straight line cannot be achieved, students should
reach some consensus about whether there is a correlation between the
two quantities. If students were able to collect two sets of data, have
them compare the two graphs.
Have students look at the Example of values and a plot from the
Background
Material: Research Activity page of the Science Education Gateway
Sunspots lesson. The plot indicates a roughly linear correlation. Each
point in the plot shows visible light sunspot area vs. areas of intense
x-ray activity. Although the scatter of the points looks bi- or even tri-modal
(three different slopes), the plot has a consistent average slope, with
about the same number of points falling above and below a central line.
Since the scale of the x-ray axis is an order of magnitude (x10) greater
than the sunspot axis, the degree of vertical scatter is not too surprising.
The sample data can be shown to students; however, students should not
be concerned with their data looking just like the sample. Every researcher's
measurements will be a little different.
Have students discuss whether or not they see a correlation between the
two values. As they discuss, remind students that even now scientists
have not determined the existence of a definite correlation.
If the class was able to generate two sets of data, and therefore, two
graphs, have students compare and contrast the two. Ask students to discuss
possible reasons why the two graphs differ from each other.
Possible reasons
include:
- Different colors were included in the x-ray areas
- The visible light sunspot areas have far fewer pixels, and so
are much more sensitive to small differences-one pixel more or less
may be quite significant.
- The exact scale of the x-ray image color scheme in counts/pixel
is unknown.
- Compare the depth of the x-ray corona, which extends far out into
space, with the small, finite thickness of the photosphere where
sunspots are located. The x-ray disturbances seen in the images
may have shapes and sizes that vary rapidly, especially near the
edge of the solar disk.
- Pixel size may not be a convenient unit of measurement.
Ask students:
- How do we know if the differences between the points are due
to scatter in the data or error on our parts? (This is a thought
question. Students should spend time considering how scientists minimize
error in measurement. Students should suggest that there were probably
inconsistencies in the way different groups measured area.)
- Describe some difficulties you encountered when measuring sunspot
and active region areas on the images. (Students will give
varying answers depending on the types of difficulties they faced.
Students will probably note that delineating the exact area of a sunspot
and particularly an active region was difficult with the mouse. Also,
because a pixel is an exact unit with a definite size, it may have
been difficult only covering the areas of the sunspots and active
regions.)
Assessment
Students should be able to answer the following questions
using the knowledge and skills learned through this activity as well as
the first lesson in this sunspots series.
Ask students:
- How is technology important in gathering information about the
sun? (Students should mention telescopes, satellites, and various
imaging techniques that gather information about various aspects of
the sun.)
- How do you think technology has allowed us to better understand
the relationship between sunspots and active regions on the sun?
(Sunspots are visualized through visible light imaging whereas
active regions are visualized through x-ray imaging. The use of these
two technologies allows us to capture two different types of images
of the sun at the same time. These images can then be analyzed to
determine a correlation between sunspots and active regions.)
- Scientists continue to debate whether or not there is a correlation
between sunspots and active regions. What types of technology do you
think are needed to confirm whether or not there is a correlation?
(Students should brainstorm various ideas. The aim of this question
is to have students consider how new technologies must be invented
to answer certain questions about the world. For example, the telescope
was invented to better visualize solar bodies. Similarly, in studying
the sun and determining the type of relationship between active regions
and solar bodies, new technologies must be invented which will gather
specific information about size, shape, location, and other important
details.)
Extensions
Follow this activity with the third lesson in the Science
NetLinks series, Tracking the Movement
of Sunspots.
Another lesson in which students measure the area of sunspots can be found
at the Yohkoh Public Outreach Project site. The lesson, Using
the Computer to Measure Sunspots, has students use image processing
software to view and magnify images taken by the Yohkoh satellite. Students
download specific images from the website and learn to convert the images
from GIF to TIFF format.
SpaceWeather.com has listed history's biggest sunspots in tabular form
from 1874 to the present. The data includes the date the sunspot was observed
and its area. Students can graph this data and determine in what years
the largest sunspots were observed. Graphing the data will also allow
students to determine trends in the size of sunspots over time. The data
can be found at History's
Biggest Sunspots.
Created :01/28/2002
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