How Big is a Sunspot?


Sunspots look like little splotches or specks of dirt, but they are actually magnetic storms on the Sun which can be many times larger than Earth.  These solar storms shoot dangerous particles out into space.  The particles can damage satellites, disrupt communications networks, and even cause power outages on Earth.  Analyzing the size and location of sunspots helps scientists predict and prepare for the effect of the solar winds on Earth.

Investigation One:  Estimate the size of sunspots

In March, 2001 the largest sunspot in over ten years was observed.   You can use a picture of this large sunspot to compare its size to Earth.   The Sun is 1,000 times larger than Earth. The diameter of Earth is about 8,000 miles.

    * March 29, 2001 solar image
    * metric ruler
    * compass
    * pencil

1. Print/copy the March 29, 2001 solar image taken at the National Solar Observatory on Kitt Peak.  Print image
    of the sun.
2. Measure the size of the solar image to make sure it is about seventeen centimeters across.  The scale of a solar image this size is
    1 millimeter = 4,670 miles.  (Calculate the scale for a different size image.)
3. Draw a circle 1.7 millimeters in diameter on the sun's surface and label it EARTH.
4. Measure each of the sunspots in the image and compare them to the size of Earth.

* Do you think that sunspots are big or small events on the Sun?
* Do all sunspots affect the Earth?
* How does the location of sunspots affect the earth?

    * To get an idea of just how big our sun is draw a circle nineteen millimeters in diameter and label it JUPITER.
    * Draw a line about five centimeters from the earth across the surface of the sun.  This line represents the distance from the Earth
        to the Moon: 240,000 miles, which is the farthest distance into space that humans have traveled.

Learn more about the size of the sun.

Investigation Two:  Calculate the size of sunspots

You can calculate the size of sunspots in any picture of the sun by using the formulas below.

    * March 29, 2001 solar image
    * metric ruler
    * calculator
    * pencil

1. Measure the diameter of the solar image (DS) in millimeters:
        DS = ____mm.

2. Divide the actual diameter of the sun (864,000 miles) by DS to establish the scale of the image:
     864,000 ÷ DS = ____miles per millimeter.

3. Measure the size of the sunspot (SS) in millimeters.  Multiply by the scale to find its size in miles:
     SS x miles per millimeter = ____miles.

4. Find the size of the Earth by dividing the diameter of the Earth (8000 miles) by the scale:
     8000 ÷ miles per millimeter = ____millimeters for the size of the Earth.

5. Find the size of Jupiter by multiplying the size of Earth in millimeters by 11.19:
     Earth size  x 11.19 = ____millimeters for the size of Jupiter.

6. Find the distance to the moon by dividing 240,000 miles by the scale:
     240,000 miles ÷ scale = ____millimeters for the distance to moon.

* How does knowing the relative sizes of Earth, Jupiter and the distance from Earth to the Moon help you understand the scale of the Solar System?
* Why do scientists track the size and locations of sunspots?

Look at more large sunspots.

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