Lab 7: Sunspots

Credit/Permission: For text, © William Amsberry, David Jeffery. For figures etc., as specified with the figure etc. / Only for reading and use by the instructors and students of the UNLV astronomy laboratory course.

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Favorite Report: Y / N

Task Master:

All the Tasks are linked here so that you can find them in the context of the lab exercise---which should be useful when completing your Report Form.

Task 1: Definitions.
Task 2: Sun Images.
Task 3: Sunspot Size.
Task 4: Measuring the Sunspot Positions.
Task 5: Calculation of the Synodic Period of Rotation.
Task 6: Sidereal Rotation Period. Optional at the discretion of the instructor.
Task 7: Sunspot Counting.

End of Task

Task 1: Definitions:

Define briefly in your own words:
1. Sunspots:

2. Photosphere:

3. Rotation vs. Revolution:

4. Solar Cycle:

5. Sidereal Rotation Period:

6. Synodic Rotation Period:

End of Task
Task 2: Sun Images:
We will measure how long it takes a sunspot to complete one rotation of the Sun's surface. This will help us establish the synodic rotation rate of the Sun. With that information, we will then be able to calculate the sidereal rotation period.
The easiest way to determine the period of rotation of the Sun would be to find a sunspot and just watch it until it comes back around the Sun to the same place in the images. However, due to the nature of the life of sunspots, there is no guarantee that the sunspots you choose will survive an entire rotation.
Sub Tasks
1. Run the CLEA program on the desktop on the lab computers by clicking on the Solar Rotation icon (red icon).
2. Choose File/Log in.
3. Type your names and table number.
4. Choose File/Run and the main data windows will appear
5. Choose File/Image Database/Image Directory/load . A Load Image Directory window will appear.
6. Click on the a2list.txt , then click Open to load the database. The times for available images of the Sun will appear in the Image Database Directory window. Scroll down the window to see what dates are available.
7. Select 12 images by double clicking the left mouse button. It is recommended you start after 5/15/2002 and end no later than 6/30/2002. Choose ONLY ONE image PER DAY and make sure you choose the same time each day. If the time you originally chose is NOT available for a day, then pick the next closest time. Do NOT skip a day. The dates and images will appear in the Loaded Image List window. An image display window will also open showing you the last image you loaded. If you select them out of order, on the loaded image list panel, you may mouse right click → Sort Image List.
8. Go to the top of the list and click on each image in turn to see how the sunspots change from day to day. Also, you can animate the images by choosing Images/Animation/Start on this image display window. You can stop the animation by choosing Animation/Stop from the same menu.
9. Questions:
  1. Watch the sunspots. In which direction (Left/Right) does the Sun rotate on these images? __________
  2. Which side of the image is North (Top/Bottom/Left/Right)? ___________
  3. Which side is Westward (Top/Bottom/Left/Right)? ___________
End of Task
Task 3: Sunspot Size:
We will measure the sunspots and compare them to the size of the Earth to get some perspective of these objects.
Sub Tasks:
1. Pick an image that has a large sunspot somewhere near the midpoint in its rotation. To start measuring:
2. In the window that displays the image, point the cursor to the sunspot you want to measure and click. A small window appears with digits to indicate the position of the cursor in pixels. You will see a magnification window that shows the area around the cursor.
3. Using the sliders (click dragging does NOT work), fine tune the cursor as close as possible to the left side of the darkest part of the sunspot. Record the X-value in the table below.
4. Using the slider, move the cursor to the right edge of the sunspot and record the X-value in the table below.
5. We will now measure the Sun using the same technique. Click on the left edge of the sun near the vertical pink line. Using the magnified image and the sliders, move the cursor to the pink line. Record the X-value in the table below.
6. Now get the measurement for the right side of the Sun and record the measurement.
7. The Sun has a diameter of __________ km and the Earth has a diameter of __________ km.
8. Fill in the table below using the formulas given below the table.
```
          Left Pixel X-Value   Right Pixel X-Value   Size in Pixels   Size in km

 Sunspot											

 Sun
```
NOTE 1: The diameter of the Sun in pixels is GREATER than the diameter of the sunspot in pixels.
NOTE 2: The Sun will have both negative and positive pixel values. Use the absolute value of both and add them to get the diameter in pixels.
MATH:
Sunspot diameter in kilometers (km) = [(pixel diameter of sunspot)/(pixel diameter of the Sun)]*(diameter of the Sun in km)
Divide the Sunspots in kilometers by the diameter of the Earth in kilometers (km) to get the relative size of the sunspots in Earth diameters (i.e., (Sunspots in km)/(diameter of the Earth in km).
The sunspot is __________ times the size of the Earth.
End of Task
Task 4: Measuring the Sunspots Positions:
Sub Tasks:
1. To start measuring sunspot positions, follow the same procedure for measuring the sunspots above. Use the magnified image to center the cursor on the sunspot. When measuring sunspot positions, there will be a small screen labeled Sunspot Measurement Data.
2. Using the Loaded Image List, scroll to the first image and find a sunspot somewhere near the equator on the leftmost (West) side. Call it sunspot A. In the Sunspot Measurement data screen, fill in the bod Spot ID with an "A". Then press Record. DO NOT PRESS FINISHED.
3. The Record button will save the Sunspot ID, the image date and time, and the sunspot position. It will also leave a green box around the sunspot and label it "A".
4. Follow the same procedures with two other sunspots and label them B and C. DO NOT PRESS FINISHED.
5. Measure the position of the sunspots A, B, and C, on each day until it either fades away or rotates off the right edge of the sun.
6. When you have recorded the last sunspot on the l;ast image, Press FINISHED. If you do NOT press FINISHED after the last recording, ou will NOT be able to proceed. The Calculation steps will be greyed out.
7. Finally, print the recorded information. Choose File/Measurement Data/View . The Sunspot Positions Measurement window will appear.
8. Choose List/Print.
End of Task
Task 5: Calculation of the Synodic Period of Rotation:
Sub Tasks:
1. To plot and analyze the sunspots, from the main menu choose Analysis/Plot Fit Data.
2. The solar Rotation Analysis window will appear. Choose File/Dataset/Load/Longitude Values for Spot A. The data plots will appear on the grid. The x-axis is the time and the y-axis is the longitude. A straight line will show you the longitude per time unit, or in other words, the degrees of rotation per day.
3. The line that appears will assist you to find the best fit. Use the sliders to get the line to go through all of the points as best as possible. The Fit (RMS Degs) should be less than 0.5. One slider will rotate the line and the other will move it up and down. Use the Coarse function to move it quickly and the Fine function to move it slowly.
4. Record your data by choosing on the Analysis window menu bar: File/Record results.
5. Do the same steps for the B and C sunspots.
6. When complete, print the graphs by choosing File/Print Window.
7. Go back to the main window and choose Analysis/Results List and then choose File/Print.
End of Task
Task 6: Sidereal Rotation Period:
In Task 5: Calculation of the Synodic Period of Rotation, you measured the observed (synodic) rotation period. Remember that as the sunspots are going around the Sun, we are orbiting the Sun in the same direction. Therefore, the time in which we see the sunspots cross the surface is greater than what it really is. We must correct for the motion of the Earth in order to determine the sidereal period: i.e., the rotation period relative to the observable universe which can be justly called absolute rotation.
Sub Tasks:
1. To determine these two periods, we first need the observed rate of motion of the sunspot. The slope of the sunspot longitude versus the time line is that rate of motion in degrees per day. Use your graphs from Task 5: Calculation of the Synodic Period of Rotation to calculate the slopes for your "observed" sunspots and then enter them and the sunspot latitudes below in Table: Sunspot Synodic and Sidereal Periods.
2. The exact calculation of the sidereal period requires the rotation period (relative to the observable universe) of the Earth around the Sun: i.e., the sidereal year = 365.256363004 days (J2000). However, as a simplification use Julian year (Jyr) = 365.25 days exactly by definition which is an adequate approximation for the correction.
3. The formulae for synodic period and sidereal period are, respectively,
```
  SYN(days)=(360°)/[Rate(°/day)] and  SID(days)=(SYN*365.25)/(SYN+365.25) . 
```
  Using these formulae calculate the synodic periods and sidereal periods for the sunspots you "observed" and enter the values below in Table: Sunspot Synodic and Sidereal Periods.
```
_______________________________________________________________________________________
Table:  Sunspot Synodic and Sidereal Periods
_______________________________________________________________________________________
Sunspot ID   Latitude        Rate       Synodic Period  Sidereal Period
             (degrees)   (degrees/day)      (days)           (days)
_______________________________________________________________________________________
	
  A
	
  B

  C

                                                         Average Sidereal Period

_______________________________________________________________________________________ 
```
4. Animate the images. Which of the sunspots have the longest lives? The large or the small ones? _______________
5. Pick the largest sunspot about to disappear off the East edge. Knowing the Synodic period, how many days later should you expect it to reappear on the West side (if it survives)? _______________
6. Does latitude of the sunspot change? Do they go North and South or just West to East? ______________
End of Task
Task 7: Sunspot Counting:
Sub Tasks:
1. Choose an image that has a good number of sunspots on it. You will now estimate the number of sunspots using the statistical grouping and number method.
2. Count the groups of sunspots. A group can be anywhere from one single sunspot to a cluster of several sunspot. To count as a group they all need to be close together. G = _____________
3. Count the individual sunspots. N = _____________
4. For statistical purposes, solar researchers have devised the Sunspot Number, R, Calculated as follows: R=(10*G)+N
5. What is your R? _____________
6. Does the number of sunspot vary from year to year? _____________
7. Is the variation of the number of sunspots periodic? _____________
8. If so, what is the variation period? _____________
9. What is the reference value for the number of sunspots on the date you chose? (Hint: Google "Sunspot count for [month] [year])." _____________
10. Does the number R you computed above agree with the number of sunspots from references of the same date? _____________
11. The sidereal period of a point on the Sun near latitude 75° is about 33 days. How this compare to what you computed? (longer/shorter) _____________
12. Does this mean the Sun rotates like a solid body or like a fluid body? _____________
13. Explain your answer. ________________________________________________________________
End of Task