observing and analyzing sunspots

The magnetic North pole is the point to which the needle of a compass points. The magnetic North pole is not in the same place as the 'real' North pole, the point where the (imaginary) rotational axis of the earth sticks into the ice. The magnetic pole wanders all around the northern wastes, and it is in a different place from year to year.
Here is a map of where the magnetic pole has been since 1831, and another map that goes from 1600 to 2000.
The difference between magnetic and true north differs from place to place. To find what it is where you live, check out this interactive site, or call a nearby airport.

  How to set up the sunspotter:
The first thing to do is to align the sunspotter with true North. There is a small compass on a string. On the base there is a line, which points to the local magnetic north. Put the compass over the line, and rotate the whole sunspotter until the line is aligned with the compass' North-South direction. The base of the sunspotter now points to true North.

Next use the three adjustable feet to level the base. There is a bubble level glued to the base for this purpose. After leveling, re-check the compass to make sure the thing hasn't moved off North during leveling.

  How to point the scope at the sun:

Loosen the knob for gross adjustment of the rotation. Hold the scope while you do this so it does not slam down. Rotate the scope so it roughly points at the sun, and tighten the knob again.

Loosen the big knob for gross up-down adjustment. Hold the scope while you do this, so it does not slam down. Move the scope up or down to roughly point at the sun. Tighten the knob again.

Use the big wheel for fine-adjustment of the rotation. This allows you to smoothly follow the sun's movenment in the 'horizontal' direction,

And use the knob under the front end of the scope to fine-adjust image of the sun onto the card holder in the vertical direction. If you are leveled and pointed to true North, this will not be necessary very often.

After following the sun for a while, the piece that moves the disk has rotated clockwise to the end of it's range, and you won't be able to follow the sun any more. Crank it all the way back again, and use the gross-adjust knob to point the scope at the sun again.

The same can happen in the vertical direction.

  How to take data:

Slip an index card into the card holder, all the way down. This card should have a circle drawn on it that exactly matches the image of the sun. (Make a bunch of cards like that, making sure that the circles you draw are in precisely the same place on each card.) Use the fine adjusts to get the image of the sun to coincide with the circle.

  How to analyze the sunspot data:

Take your index cards and see if there is one particular sunspot that you can follow over several days. Use the pantograph to enlarge the sun's image, and to copy all locations of the spot onto one sheet of paper. By each dot, copy the date.

Find the middle of the sun's outline, and with a compass draw a nice circle over the outline you traced with the pantograph.

Draw a line that roughly goes through all the points, and then draw a line perpendicular to the first one, and also goes through the middle of the sun.

Off to the right, draw a circle with the center on the last line, and with a radius equal to the sun's outline you drew in step 2. This is the sun as if you are looking down at it from the top.
Now draw a line parallel to the last one, and that goes through the point where the the sunspots would disappear around the side of the sun (by the arrow)
Draw a smaller circle that just touches this line. This smaller circle is the path that the sunspots would follow if we were looking down on the top of the sun.

Now draw a line parallel to the main axis, from the first sunspot to where you just cross the small circle. Repeat for all other sunspots.

Here I have shown the right-hand side of the sheet, and rotated it such that the last lines that you drew are shown coming from the top. Where those lines intersect the small circle is where the sunspots would be if you were looking at the sun from the top.
Draw a line through the center of the circle. The orientation does not matter much. Then draw lines from the center to each of the intersection points.

Now get out your protractor and measure the angle between the big horizontal line and each of the lines you drew from the center to the sunspots. Make a table of this angle and the date and time when you observed this sunspot. Make a third column showing how much the angle changed since the previous day.
date and time angle in degrees difference from the previous day
12 March 98 11:30 260 -
13 March 98 11:40 470 210
14 March 98 11:25 660 190
15 Match 98 11:32 860 200

STEP 8a:
For the final step, there are a few options. This paragraph is for those grades where the kids are supposed to be able to plot graphs. In this version, we will plot the angle (column 2) versus the date/time (column 1). Then we'll read off the rotational period from the graph.

STEP 8b:
For the final step, there are a few options. This paragraph is for those grades where the kids can't make the graph like we did in 8a. Instead we will calculate how many degrees the sun moves per day, on average, and get to the rotational period from there. We'll use the numbers in column 3 for this.

Last update 2 April 2004 --