Day Lab Part 2: Measuring the Rotational Period of the Sun

The second experiment we conducted was intended to determine the rotational period of the sun by tracking the movement of sun spots along the surface of the Sun. We initially attempted to conduct the experiment using the naked eye and equipment in the lab. However, the conditions were not conducive to collecting adequate data so we settled on using prerecorded images of the Sun's rotation. We were able to track the movement of sunspots by placing a gridded plastic sheet over the computer screen and marking the time it took for a sun spot to travel from one line of longitude to the next.

Archival Data, Courtesy: Steven Johnson

The Gridded Plastic Sheet, Courtesy: Steven Johnson

James Hillenbrand and I teamed up to track the movement of the sunspots. We decided to track sunspots at three unique solar latitudes over 30 degrees. These are the average times that we recorded for such a movement:

Trial 1(+\(40^{\circ}\) latitude): 48.1165 hours
Trial 2(\(-10^{\circ}\) latitude): 56.8166 hours
Trial 3(\(+5^{\circ}\) latitude): 54.05 hours

The average time out of these three trials for a sunspot to move 30 degrees was 52.99 hours. However, this is only a fraction of the total rotational period of the Sun. In order to calculate the full period, we set up the following proportion where X is the total period:
\[\frac{30^{\circ}}{360^{\circ}}\:=\:\frac{52.99\: hrs}{X}\]
\[X\:=\:12\:\times\:52.99 hrs\]
\[X\:=\:635.93 hrs\:\approx\:26.5\:days\:\approx\:2289357.6\:seconds\]

After completing this calculation, we knew that the rotational period of the Sun was about 26.5 days.