PURPOSE

MATERIALS

1. Internet access via Web browser, e.g., Netscape Communicator or Microsoft Internet Explorer
2. Pencil, metric ruler, and hardcopy of near-real-time solar telescope imagery (showing sunspots)
3. Calculator

PROCEDURE

1. Use a Web browser to access The very latest SOHO images Web page. Download/print the latest MDI Continuum solar image.
2. In the following data table, record the image date and time. [Note Date/Time format: Date = yy/mm/dd; Time = UTC. Refer to a Time Conversion Chart to convert UTC to EST/EDT.]
3. Using a metric ruler and the hardcopy solar image, carefully measure the diameter of the Sun (mm) and the width (mm) of the largest sunspot (along major axis); record these data in the data table (below). Circle and label the largest sunspot (e.g., "largest").
4. Answer the Activity Questions.

DATA

ACTIVITY QUESTIONS

1. Use a proportion (two equivalent ratios) to solve for the actual size of the largest sunspot. Show your work (below); record your answer in the data table (above).

    s     S
   --- = ---
    d     D
   
   Where:
      s = Scale Model Size of Sunspot
      d = Scale Model Diameter of Sun
      S = Actual Size of Sunspot
      D = Actual Diameter of the Sun (1,400,000 km)
   
   Substitute, cross-multiply, do dimensional analysis, solve for "S":
   
    s (mm)        S (km)
   -------- = --------------
    d (mm)     1,400,000 km
   
             s (mm) x 1,400,000 km
   S (km) = -----------------------
                    d (mm)
   

   If the scale model size of the largest sunspot = 3mm, then its actual size would be approximately 24,706 km wide.

2. Compare/contrast the size of the largest sunspot with the diameter of the Earth (12,735 km). Approximately how many Earth diameters would fit inside the Sun's diameter? Show your work; circle your answer.

   If the scale model size of the largest sunspot = 3mm, then its actual size would be approximately 24,706 km -- nearly double the Earth's diameter! Approximately 110 Earth diameters would fit inside the Sun's diameter (1,400,000/12,735 = ~110).

3. The hardcopy MDI Continuum solar image is really a scale model of the Sun. Use the Sun's scale model diameter and actual diameter to determine the scale of the image (you may need to refer to a brief tutorial on determining fractional scale). Show your work; circle your answer. Use the image scale to estimate the size of two other sunspots; record the estimated size of these sunspots in the data table (above). Circle and label the two sunspots (e.g., "No. 2," "No. 3").

   The scale of the image = 1/8,240,000,000 (1,400,000,000,000 mm/170 mm = ~8,240,000,000). Features on the Sun are nearly 8.25 billion times larger than the image!

APPENDICES

1. The very latest SOHO images
   http://sohowww.nascom.nasa.gov/data/realtime-images.html
2. Time Conversion Chart
   http://www.wsanford.com/~wsanford/activities/timeconv.html
3. Determining the Fractional Scale of a Map or Scale Model
   http://www.wsanford.com/~wsanford/activities/scale.html
4. Converting Metric Units - Use the following list of metric units to count the number of units change, then move the decimal point (in the same direction in which you were counting) one place for each unit of change:

   (largest) km hm dam m dm cm mm (smallest)
                       2--1--0
                       <------      
   

   For example, convert 1,100 cm to m by moving the decimal point 2 places to the left: 1,100 cm = 11 m (approximately 36 feet).