Some Examples of Strategies for the Rotation Activity

Below are a couple of methods students might come up with. It is important to note that we do not intend for this list to be comprehensive, and in fact we hope that the students will come up with ideas that escaped us!

1. Students track the movement of a particular sunspot over the course of a few days days. They then measure the distance the sunspot moves across the image of the sun in a day and divide this number into the observed circumference of the sun at the sunspot's latitude. ("Observed circumference . . ." refers to the number arrived at by multiplying the width of the sun's image at the given latitude times Pi). This should yield the sun's approximate rotational period.
   
   
2. Just like the above method, except that the spot's movement over the course of, say, five days is measured. This quantity is then divided into the observed circumference of the sun, and the result is multiplied by the number of days, five in this instance.
   
   
3. This method might occur to kids who are a bit less trusting of math. It is essentially the same as method 1, but is less analytical (as such, a discussion comparing the two methods can be very helpful to those kids who need to work on their level of comfort with math). Basically, a string is used to measure the circumference of the Sun, and a ruler measures the distance d a spot travels in a day. At this point, there are a few variations, but the basic idea is that they count how many times d will fit into the measured circumference. Of course, this counting is a way of doing division, and it is important that the kids see this.
   
   
4. Students could count the number of days it takes for a sunspot to get from the center of the sun's image to the very edge. This corresponds to a fourth of a complete rotation, so four times this number of days should be the approximate rotational period. This is clearly the simpler idea to understand, but it may be difficult to implement with much precision, since it can be surprisingly hard to see when a spot gets to "the very edge."