Practical exercise 1: LET’S TRACK THE SUNSPOTS

Aim

Students will work with real images of the Sun which proffesional astronomers all over the world work on. They can follow the changes of sunspots even for a short time and can determine the speed at which they move on its surface.

Necessary materials

At the Appendix you will find images of the Sun during 5 days obtained by the solar observatory SOHO, also a chart of the Sun on which the coordinates – length and latitude are marked.

Instructions for the teacher

Divide the class in temas with two students. Have each team to track one or more of the spots groups marked on the solar images.

Detailed instructions for students

1. Each of the teams must trace the change on the surface of the Sun of one or more of the three groups of spots - A, B or C.

2. For each day one of the team should mark the position of the sunspots group. The other team member should write in the table one of the coordinates (the longitude) of the sunspots group for the day. For example spots A are located at latitude -75 degrees on 28.03. The images have been taken every day at one and the same time with the exception of 31.03 which will give a small error for this day.

3. Exercise result:

1. At the end you should have tables as follows:

Sunspots groups

4. The next task is to determine how many degrees in length the spots move in 1 day. To determine this we need to see the initial and final length of the spots - on the first day (28.03) and on the last day (1.04). Then divide the difference in length by 5 (five days). For this purpose we must use the map where we have marked their positions. As a result, we have the speed in degrees at which the spots move on the surface of the Sun. Do all teams agree with the set speed? Is there a difference between the different groups of spots? [Answer: Within a certain error from the measurements of the individual teams, the result should be the same: the average speed at which the spots move is about 12 degrees per day.] Question: Do the spots change shape and size? [Answer: Yes, because they are active formations.]

5. The final question in this exercise is: How long does the Sun make a 360 degree orbit? Can we determine this with the spot data we received? We must keep in mind that the Earth also moves around the Sun in the same direction at a speed of about 1 degree per day. So for our calculations we have to add 1 degree per day to the visible movement of the Sun (apparently it seems that the Sun is moving slower than it actually is). [Answer: The result of the calculations shows that the Sun rotates every 27 days around its equator, where the spots are observed.] It should be noted that the Sun does not rotate like a solid body, so its speed of rotation at the equator and at the poles is not the same.