This applet has been designed as an interactive tool for students to explore solar rotation. Students observe and track sunspots on the solar surface over a period of days. The applet consists of 4 separate activities. As a whole, these activities will help reinforce the concept of solar rotation and will give students an opportunity to both perform scientific calcualtions and to reflect on those calculations.
In this activity, students simply observe the movement of sunspots across the solar surface. The animation shows solar images over a period of 35 consecutive days. Students can also identify the varying sizes and shapes of sunspots.
In this activity, students begin by clicking on the "Calculate linear rotation" button. This will open a window in which students will input information. Students will then select one of the drag markers (2) and drag it to the surface of the Sun, positioning it directly overtop of one of the sunspots. It is best to position the marker on a sunspot at the far left-hand side of the sun. At this time, students should input the start date and time (3) into the information window. Students will then use the fast-forward button (4) to advance the animation one frame at a time. Once the marked sunspot nears the far right-hand side of the Sun, they should position a new drag marker (2) overtop of the sunspot and input the new date and time (5) into the window. Students will then click on the "Show/hide ruler" button (1) to display the ruler. Students are to measure the distance between the sunspot markers and also the overall width (diameter) of the sun. The results should then be inputted into the information window (6 & 7) and students can click the "calculate" button (8) to perform the calculation. The solar rotation rate will be displayed based on the calculations for the given sunspot.
Students should write down the rotation rate and attempt the calculation a second and perhaps third time, selecting different sunspots to track each time.
Students should find that the rotation rate depends on the vertical location of the sunspot. This phenomena is called "differential rotation," and is due to the fact that the Sun a huge ball of gas and does not have a solid surface.
This activity is similar to activity 1 in that students are to again observe sunspots and determine a rotation rate. However, in this activity, students will use an angular calculation. Students begin by clicking on the "Calculate angular rotation" button. Students will then select and mark (3) a sunspot and input the date and time into the information window. The animation can then be advanced as before (4). Students will then position a new marker (3) to mark the new location for the sunspot and input the new date and time (5). Students can then click on the "Show grid button" (1), which will display a spherical angular grid over the surface of the Sun. Knowing that each grid line represents 15 degrees, students will then calculate the angular distance that the sunspot moved and input the result into the information window (6). Students will then click the "Calculate" button to display the solar rotation rate based on the calculations for that given sunspot.
Students should write down the rotation rate and repeat the process for at least one more sunspot. Again, differential rotation will be detected.
Students also should be asked to think about the difference between their results from the linear approximation and the angular calculations. The differences stem from the fact that the solar surface is spherical, not flat, remembering a complete sphere has 360 degrees.
The last activity that can be done using the applet is a calculation of the size of the sunspot. Students begin by clicking on the "Calculate sunspot size" and "Show/hide ruler" buttons. Students can then measure the diameter of the Sun (2) and the size of one of the sunspots (3) . After inputting the information, students can click the "Calculate" button (4) to display the actual sunspot size in kms.
Students should then be asked to repeat the calculations to determine the size of the umbra (the dark center spot) and penumbra (the larger grey outlining) of the sunspot.
Students could then be asked to reflect on these sizes in comparison to the size of Earth.