Guided by the Stars

Research Question:

How can you use the North Star to find your latitude?

Before high-tech navigational devices, sailors used the North Star to figure out where they were located. You can build your own astrolabe, which works based on where the North Star is in the night sky, to find out what the latitude of your location is.

Materials:

• Ruler
• Protractor
• String
• Scissors
• Metal nut
• Pencil
• Map

Experimental Procedure

• Measure the radius of the protractor. In other words, measure the length from the middle of the flat side until the middle of the rounded side.
• Cut a piece of string that is twice the length of the protractor’s radius.
• Tie one end of the string to the center of the straight edge of the protractor.
• Tie the other end of the string to the metal nut.
• Cut two shorter piece of string, about four inches long.
• Bind the pencil to the straight edge of the protractor using the two pieces of string.
• Go outside on a clear night. Find the North Star.
• Put the back end of the pencil by your dominant eye and point the front end of it towards the North Star.
• Without moving the protractor, move your head around so that you can see the side of it. The string should be hanging down onto or near one of the numbers on the curved side of the protractor. That number should be the same as your latitude.
• Find the latitude of your city on a map. How accurate was your astrolabe?


Terms/Concepts: Latitude; Longitude; North Star; How did sailors use the North Star?

References:

• Experiments You Can Do in Your Backyard, edited by Joanna Callihan and Nathan Hemmelgarn. Pp 60-61.