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    Navigation: Lost at Sea!

Overview : 

In 1641 the treasure-filled Spanish galleon Concepción set sail for Spain from Havana, Cuba.  Days later a hurricane ravaged the ship, and her pilots decided to sail to the nearest Spanish base, Puerto Rico, for repairs.  A month later the pilots thought they were north of Puerto Rico, so they sailed due south. They were actually north of what is now the Dominican Republic and a treacherous coral reef.  Soon the Concepción ground into the reef and sank, spilling the riches that would give the reef its name: Silver Bank. 

The Concepción was doomed because the ship’s pilots made a mistake in determining her location. Location can be expressed in a number of ways (with a street address or map coordinates, for example).  This lesson explores the concept of location and allows students to create their own tools to determine their location on the Earth’s surface. 

Connections to the Curriculum:

  • geography, mathematics, natural science, history, language arts 

Connections to the National Geography Standards: 

  • Standard 1: “How to use maps and other geographic representations, tools, and technologies to acquire, process, and report information from a spatial perspective”
  • Standard 17: “How to apply geography to interpret the past”
  • Standard 18: “How to apply geography to interpret the present and plan for the future”
Time:
  • One to two hours in the classroom plus a half an hour at home

Materials Required: 

  • globe or map with latitude and longitude lines
  • photocopies of a 6- to 8-inch quadrant with visible degree marks (you can download a quadrant image from the Event Inventor)
  • pieces of cardboard roughly the size of the quadrant
  • drinking straws 
  • 12-inch pieces of string
  • tape
  • paste
  • scissors
  • small metal weights that can be tied to the string (e.g., washers, keys, binder clips)
Objectives: 
    Students will learn about the historical use of quadrants for navigation, construct their own quadrants, measure their location, and report and compare their results. 
     
Suggested Procedure
 

Opening: 

Tell the story of the Concepción and explain its fate.  (You may want to copy the above map onto a transparency to illustrate the course of the Concepción on an overhead projector.)  Explain that the ship’s pilots miscalculated their location, and emphasize the role location played in the Concepción’s sinking. 

Development: 

  1. Review some ways of identifying location.  While street addresses are useful for some purposes, latitude and longitude coordinates are better for others, such as navigating a ship at sea.  Explain that latitude is the angle in degrees north or south of the Equator.  Longitude is the angle in degrees east or west of the Prime Meridian, the imaginary line that connects the poles and runs through Greenwich, England.  Illustrate how latitude and longitude coordinates are used to locate places on a globe or map.

  2. Distribute the supplies. 

  3. Instruct the students to make their own quadrants by following these steps: 
    • Paste the copy of the protractor onto the cardboard, and cut the cardboard along the edges of the protractor copy. 
    • Tie one end of the string around the middle of a drinking straw. 
    • Tie the other end of the string to a weight. 
    • Tape the straw along the straight edge of the cardboard protractor, making sure that the knot in the middle of the straw is at the center of the straight edge. 
    • Cut the ends of the straw even with the ends of the straight edge.
    • Tell them they have just made a quadrant and explain what one is.

  4. If you’re in the Northern Hemisphere, discuss the North Star (Polaris) with your students. What is it? Where is it? Let them know they can find the North Star in two ways:  First, using the Big Dipper as a guide, follow a straight line out from the two stars that make up the end of the “bowl” of the dipper. The first fairly bright star is Polaris. Second, locate the end star in the handle of the Little Dipper. This too is Polaris.

  5. As a homework assignment, ask students to go outside on a clear night. Have them hold the quadrant so that the straw is at the top and look through the straw (like a telescope) at the North Star. The angle between the weighted string and the 90 degree line on the quadrant is their latitude in degrees north of the Equator.

    If you’re in the Southern Hemisphere, your students can use the sun to calculate their latitude as explained by the USGS Learning Web.  The straw in your students’ quadrants plays the role of the pencil in this lesson plan. Your analemma corrections in step four of the USGS activity will be the reverse of those used in the Northern Hemisphere. (Remind your students never to look directly at the sun.) 

  6. In class have students compare their results. One way to show results visually is by creating a bar chart that plots the number of students who obtained various latitude readings.
Closing: 
Ask students to think about the accuracy of their data.  How widely do their results vary?  Discuss how easy or hard it might be to use a quadrant on a rocking ship.  How could students increase the accuracy of their measurements? Would a longer or a narrower straw help? 

Suggested Student Assessment: 

  • quadrant readings (homework check)
  • discussion participation

  •  
Extending the Lesson:  

Sailors could determine their latitude with quadrants, but to accurately determine their position, they had to know their longitude as well. Many of our modern seafaring terms come from the way sailors calculated their longitude. 

Open a discussion about nautical words and expressions by asking students to list as many of these words as they can. Write some of the words on the board and discuss their meanings and origins.  If the words “log” and knots are not part of the list, add them, and then ask students “ Why do we enter information into a ‘logbook’?  Why are nautical miles measured in knots?”  

Sailors used direction, time, and speed to determine their longitude. They used a compass to measure direction and a sandglass to measure time.  To measure speed, sailors tied a knotted piece of rope to a log. When the ship was moving, the crew tossed the log into the sea, and the knotted rope was pulled overboard. Using a sandglass, sailors kept track of the time it took the rope to unreel. As the rope passed through their hands, they counted the number of knots, which were spaced at even intervals. Because they knew the distance between knots, they could calculate the ship’s speed. 

Now that they know the origin of “knots,” can students figure out where the term “logbook” came from?  (The way a log was used on sailing ships gave rise to other expressions using the word, such as logging in and out and—perhaps most interesting for students—logging on and off a computer.) 

For another hands-on activity, check out Finding Your Longitude from the Event Inventor. 

Gail S. Ludwig of the University of Missouri in Columbia, Missouri, contributed classroom ideas for Silver Bank.  

 
 


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