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How to set up the sunspotter:
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TRUE AND MAGNETIC NORTH
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 great interactive site, or call a nearby airport.
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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.
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How to point the scope at the sun
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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.
Loosen the big knob for gross up-down adjustment. Hols 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, and the knob
under the front end of the scope to get the image of the sun onto the
card holder.
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How to analyze the sunspot data:
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STEP 1:
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.
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STEP 2:
Find the middle of the sun's outline, and with a compass draw a nice
circle over the outline you traced with the pantograph.
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STEP 3:
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.
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STEP 4:
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.
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STEP 5:
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.
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STEP 6:
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.
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STEP 7:
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.
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| 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 |
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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.
(...more..)
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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.
(...more...)
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