Name ________________________
The Sun and Sunspots
I. Introduction
Sunspots were first regularly studied by Galileo. He was able to prove that Sunspots were features on the
face of the Sun itself and not objects which passed somewhere between the Earth and the Sun. We now
know that Sunspots are manifestations of magnetic fields below the surface of the Sun. These magnetic
fields interfere with the convection of material close to the surface, causing localized stagnations. This
material then cools more than the surround regions and thus appears darker. Sunspots have temperatures
around 3500 Kelvin while the average temperature of the Sun's surface is 5700 Kelvin.
Knowing that the Sunspots were on the Sun itself allowed Galileo to determine the rotation rate of the Sun
by observing the motion of Sunspots as the Sun rotates on its axis. Using the included observations, you
will do the same.
II. The Observations
Earlier this year you observed the Sun with the Sunspotter over a period of several days - this will be your
data for this lab.
Determine the Synodic rotation period of the Sun:
1. Choose a sunspot that is visible in several images. The longer the time the spot is visible, the
better. Your observations were placed on a orthographic plate, determine the Solar Longitude for your
spot group for the first and last days it is visible. You may need to redraw your diagrams. Record your
data in Table 1 below. Repeat this procedure for a second and third sunspot.
Table 1. Sunspot Data
Spot 1
Date
Longitude of Sunspot
Date
Longitude of Sunspot
Date
Longitude of Sunspot
First Observation
Last Observation
Difference
Spot 2
First Observation
Last Observation
Difference
Spot 3
First Observation
Last Observation
Difference
3. Determine the time difference between observations in days and record in Table 1 and average
them here.
4. Determine the difference in longitude between the observations in Table 1 and enter it in Table
1 and average them here.
5. Determine the synodic rotation period of the Sun as follows:
Synodic rotation rate = Average Difference in Sunspot Longitude from above
Average Time difference between observations
Synodic rotation rate =
Synodic rotation rate = ______________degrees/day
Synodic period = ______360 degrees__________
Synodic rotation rate
Synodic period =
Synodic period = ________________________ days
C. Since the Earth revolves around the Sun as the Sun rotates on its axis, to determine the true (sidereal)
rotational period of the Sun, we must correct for the Earth's motion over the course of the observations.
Determine the Sidereal rotation period for the Sun:
1. ________1________ = _________1________
Sidereal Period
Synodic Period
in days
in days
Where the Earth's orbital period in days is 365.26.
________1________ =
Sidereal Period
in days
Sidereal Period
of the Sun
= __________________ days
+
________1_________
Earth's orbital period
in days
IV. Questions
1. Do Sunspots keep a constant latitude as the Sun rotates?
2. What do you notice about the shapes of the spots as they rotate into view?
3. Propose a logically convincing argument to prove that the spots are on the sun itself.
(Hint: think about question #2)