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Activity: Determine Your Latitude

NGSS Crosscutting Concepts:

NGSS Disciplinary Core Ideas:


  • Protractor
  • Straw
  • Star map or stargazing software
  • Tape
  • String
  • Washer or bolt
  • Map or map software


Safety Note: Do not look directly at the sun, even while wearing sunglasses. Your sextant is not made to look at the sun because it does not have the appropriate filters.


  1. Construct your sextant (Fig. 8.21).
    1. Secure the straw to the straight edge of the protractor using tape.
    2. Tie a washer to one end of the string.
    3. Secure the second end of the string to the middle of the protractor. Push the end of the string through the small hole in the center of the protractor. Once the string is through the hole, tie a knot so that the string cannot be pulled back through the protractor. The string and washer should be a little longer than the radius of the protractor.

<p><strong>Fig. 8.21.</strong> Sextant</p><br />
<p><strong>Fig. 8.22.</strong> Determine angle theta above the horizon using your sextant.</p><br />

  1. Review the information about angles in Table 8.1.
Table 8.1. Information about the geometry of angles
A right triangle contains one interior angle equaling 90 degrees, indicated by a small square.
The sum of the remaining angles a and b equals 90 degrees.
  1. Develop a method to determine the angle theta (θ) in Fig. 8.22 using the angle that the sextant is showing, and use it to calculate angle theta in Fig. 8.22.
  2. Practice using your sextant in the classroom.
    1. Your instructor will choose an object in your classroom, such as a light fixture or picture on the wall.
    2. Predict the angle from your eye to the object. Record your prediction.
    3. Using the sextant with the straight side up, sight the object looking through the straw.
    4. Once the object has been sighted, have your lab partner look at the string and washer and record the angle measured on the protractor. Record this angle.
    5. Repeat steps c–d two more times.
    6. Calculate and record the average angle measurement.
    7. Compare your average calculated angle for the object in your classroom to the angle calculated by your classmates for the same object.
  3. Choose additional objects to practice using your sextant. Repeat steps 4 a–g for at least two additional objects.
  4. Use your sextant to measure latitude.
    1. Predict the latitude that your home or school is located at. Record your prediction.
    2. At night, locate the North Star (northern hemisphere) or Pole Star (southern hemisphere) using a star map. Repeat steps 4c–4f.
    3. Compare your observed latitude with that of your classmates.
    4. Using a map or map software, determine your exact latitude and record it.


Activity Questions: 
  1. What value of theta did you calculate in step 3? Describe the method you used to calculate angle theta using the geometry terms described in Table 8.1.
  2. What angle will your protractor read
    1. when the object in the classroom (step 4) is directly at eye level?
    2. when the object in the classroom (step 4) is directly above you?
  3. Was your measured angle to the objects in the classroom similar to the angle calculated by your classmates? Explain your answer in terms of
    1. accuracy.
    2. precision.
      (If you are not familiar with these terms, read Practices of Science: Precision vs. Accuracy.)
  4. How could you improve the accuracy and precision of your sextant?
  5. Compare your predicted and observed angles for
    1. the object in the classroom (step 4).
    2. your latitude measurement (step 6).
  6. Did your observed latitude measurements differ from that of your classmates? Explain why you think your measurements were similar or why they were different.
  7. Why do you think you calculated your latitude using the North Star (if in the northern hemisphere) or Pole Star (if in the southern hemisphere)?
  8. Explain what you think the following statement means: Holding the sextant at eye level above the ground affects the accuracy of the angle measurement to the object in the classroom.
  9. Do you think your sextant would be more accurate measuring large distances, such as latitude, or short distances, such as the angle between you and a picture in your classroom? Explain your answer.
  10. How would your sextant latitude measurement change if you moved to the
    1. north?
    2. south?
    3. east?
    4. west?
    5. opposite hemisphere?
Exploring Our Fluid Earth, a product of the Curriculum Research & Development Group (CRDG), College of Education. University of Hawaii, 2011. This document may be freely reproduced and distributed for non-profit educational purposes.