Sun and sunspots | Physics homework help

Materials Required

Time Required: approximately 2-3 hours

Part I. Structure of the Sun

We’ll start by looking at the solar interior more closely. Study the materials you’ll find at the Solar Interior

If you enlarge the image (by clicking on it), it shows you the various layers of the Sun. You can use this image along with your textbook to draw and label your diagram with both the inner and outer layers of the Sun.

  1. Hand draw a diagram of the Sun on the Structure of the Sun Diagram, and label each of the layers (which should include: core, radiation zone, convection zone, photosphere, chromosphere, corona). Take an image of this to insert it into your lab report.

Now use the website to read about what is occurring in each layer, and how we know this information.

  1. In your lab report below your inserted drawing, type a brief (1 or 2 sentences) description in your own words of what’s happening in each layer. Be sure to include all of the layers included in the interior and atmosphere of the Sun.

Part 2. Using Sunspots to Measure Solar Rotation

In 1611 Galileo first looked at the Sun with his telescope and was surprised to view several dark blemishes on its surface which came to be known as “Sunspots.” Upon additional observations Galileo was able to determine that these sunspots were moving across the Sun’s surface indicating that the Sun, like the Earth, was rotating on its axis. The rate that sunspots move across the Sun’s surface can be used to determine the velocity of the Sun’s rotation.  

On the Sunspot Tracking Images sheet are solar images for six consecutive days of several sunspot groups moving across the surface of the Sun taken by a NASA solar satellite known as SOHO, Solar and Heliospheric Observatory. You will be tracking three of these groups with this part of the activity. Sunspot group 1731 (near the equatorial area to the far left of the April 25th image), Sunspot group 1728 (above and to the right of Group 1731), & Sunspot Group 1730 (below and to the right of group 1731).  

Important:   In your typed lab report, clearly label all of your answers to the following questions. For any calculations below, be sure to show all of you work and not just the end answer. Make sure your worded answers are in full sentences. Any data in tables should be typed.

Identify and mark the same sunspot groups on each image (for the larger sunspot groups draw a circle around the whole group and mark a dot at the center of the circle as a reference point for your measurements). For reference, the North Pole of the Sun is the top of each image with the South Pole at the bottom. East is to the left of each image and West is to the right of each image.

  1. Which direction do the sunspots move from one day to the next? ___________

For each sunspot group, use a ruler to draw a horizontal line from the left edge of the Sun’s image through the sunspot group and end the line at the right edge.  

For each day measure the distance (in millimeters) from the Sun’s left edge to the center of each sunspot group. Create or copy the below table into your lab report. Record your data in the table.

Sun and Sunspot Groups

Date of Solar Image

Distance (in millimeters) from left edge of Sun

Group 1728

Group 1730

Group 1731







The distance that each sunspot group has traveled is the difference between the first distance entered in the table and the last distance entered in the table.  

  1. Distance travelled:  Sunspot Group 1728 ____________ mm

      Sunspot Group 1730 ____________ mm

      Sunspot Group 1731 ____________ mm

  1. Look up the Sun’s actual diameter in kilometers: ____________ km radius in kilometers: __________ km (provide your source)

From one of the solar images measure the diameter, the greatest distance across the disk, of the Sun in millimeters.   

  1. Diameter of the Sun: ____________ mm

The Scale factor for the images is simply the ratio of the diameter in kilometers (from step 3) divided by the diameter in millimeters (step 4).

  1. Scale factor: ________________km/mm

Use this scale factor to calculate the actual distance the sunspot traveled. The actual distance = the distance the sunspots traveled in millimeters (step 2) × the scale factor (step 5).

  1. Sunspot group 1728  traveled: ___________ km.

Sunspot group 1730 traveled: ___________ km.

Sunspot group 1731 traveled: ___________ km.

  1. Calculate the average distance traveled by the three sunspot groups: ____________ km.
  2. The time it took the sunspots to travel that distance was ________ days (subtract the first date from the last). 

Determine how fast the sunspots are moving across the surface of the Sun. The distance the spot traveled was calculated above. We know how long it took the spot to move this far, since we know the date of each photograph. The velocity is the distance the spots traveled divided by the time it took the spots to go that distance.

  1. The average speed of the Sun’s rotation was measured to be __________ km/day.

Each sunspot must travel a distance equal to the Sun’s circumference in order to make a full rotation around the Sun. As observed from Earth, the rotation period, or the time it takes a sunspot to go around the Sun once, is given by the Sun’s circumference divided by the rotation speed.

  1. Sun’s circumference = 2 π × radius of the Sun = _________________ km. (Remember, pi = π{“version”:”1.1″,”math”:”<math xmlns=””><mi>&#x3C0;</mi></math>”} = 3.14)
  2. Rotational period = circumference / rotational speed = ________________ days.

To know if your analysis makes sense, we should compare the measured value with the known value. The sunspots we have chosen for analysis are very close to the Sun’s equator.

  1. Look up the following in your textbook: the rotational period of the Sun at its equator is ________ days.
  2. Calculate the percent difference between your measured value and the known value of rotation period of equator:

[(measured value – known value) / known value] × 100% = ___________

You may have noticed in your calculations that the three groups of sunspots do not move across the surface of the Sun at the same velocity.  Unlike the Earth, the Sun is not a solid ball on its surface but is a state of matter known as “plasma”.   This allows to Sun to experience differential rotation of its surface.  

  1. What is differential rotation for the Sun and how does it affect the motion of sunspots on its surface?
  2. How well does your calculations match to the actual rotation rate of the Sun?  Based on your answer to Question 14, what do you believe are the sources of any errors that make your calculations inaccurate?

Part 3. The Energy of Stars.

The Sun is the energy source of all life here on Earth but it was unknown for a very long time what is the energy source of the Sun itself. Some suggestions included gravitational potential energy, energy created as the Sun gravitationally collapses in on itself, and chemical combustion, or “burning” as we would understand the term.  

But both were quickly proven to be an inadequate energy source since, even with the humongous size of the Sun, they would not be able to maintain the energy output over billions of years needed for life to evolve here on Earth. Scientists had ample evidence to prove the age of the Earth at billions of years old and it would make no sense for the Earth to be older than the Sun.

The Sun creates its energy by nuclear fusion processes in its core through what is known as the Proton-Proton Chain. In this process lighter elements are fused into heavier elements releasing energy which powers the Sun (the amount of energy released is equal to Einstein’s famous equation E =mc2{“version”:”1.1″,”math”:”<math xmlns=””><mi>m</mi><msup><mi>c</mi><mn>2</mn></msup></math>”}).  

For this part of the activity you will be viewing a Proton-Proton Chain simulation created by the University of Nebraska-Lincoln. Follow this weblink for the animation.

Astronomy Education at the University of Nebraska-Lincoln. Astronomy Simulations and Animations. Proton-Proton simulation.

There are three basic steps involved in the proton-proton chain, first the formation of 2H, second the formation of 3He, and lastly the formation of 4He, Helium, the final product of hydrogen fusion. View the animation to answer the following questions (using complete sentences).

  1. List all of the “players” involved in the proton-proton chain.
  2. Explain the first step of the proton-proton chain, the formation of 2H.
  3. Explain the second step of the proton-proton chain, the formation of 3He.
  4. Explain the last step of the proton-proton chain, the formation of 4He.
  5. These fusion reactions do not occur throughout the Sun but only deep within the Sun in its core. What conditions must be overcome for fusion reactions to occur and are they able to happen only in the core of the sun?  you will need to consult other sources for this answer)

Higher mass stars however use a different method of energy production known as the CNO cycle. For this part of the activity you will be viewing a CNO Cycle simulation created by the University of Nebraska-Lincoln. Follow this weblink for the simulation.

Astronomy Education at the University of Nebraska-Lincoln. Astronomy Simulations and Animations. CNO Cycle Animation. (Make sure to answer in your own words an din complete sentences.)

  1. List all of the “players” involved in the CNO cycle.  What players are different in the CNO cycle than in the proton-proton chain?   
  2. The CNO cycle is more complex than the proton-proton-chain but is some ways they are very similar.  In what ways are they similar? (Hint: It’s in the protons)
  3. In the CNO cycle 12C is a catalyst in the overall fusion reaction.  Describe the role that 12C has in this fusion reaction.
  4. In a paragraph (minimum of 50 words) summarize what you have learned from this laboratory activity.  

NOTE: You must provide a reference list showing the source(s) that you used, including our own textbook, in proper APA citation format.

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