Using an Astrolabe
This activity is designed to demonstrate latitude using an astrolabe.
What is an astrolabe?
"The Astrolabe is the most sophisticated of ancient scientific instruments. Designed circa 170 B.C., its use quickly spread in navigation, surveying, and astronomy."
Astrolabes have been used throughout time for astronomy and navigation. Especially during the Renaissance, the astrolabe (or mariner’s astolabe) was used to locate position as one traveled by ship. In fact, Columbus used an astrolabe on his voyage to discover the New World.
There were several different models over the years but the most important characteristic of all astrolabes is the use of degrees on a flat plate to identify latitude. As a reference point, the North Star is used. At night, one could point the astrolabe at the North Star and read the degree marking on the plate as it fell into place. To put this in perspective, if one was as the North Pole and pointed the astrolabe at the North Star, the plate should fall on 90°. Also, if one were able to see the North Star from the equator (at the horizon), the astrolabe should read 0°.
ACTIVITY: Students will, after being able to identify the North Star, use their own constructed astrolabe to estimate the latitude of where they live. Compare results.
1) Explain and discuss with students where the North Star can be found in the sky.
2) Construct an astrolabe.
Materials: a stiff sheet of paper (posterboard), a big round plate, scissors, protractor, a drinking staw, tape, string, metal washer
Directions:
- Put the plate on the piece of paper and trace a circle with the pencil.
- Use the scissors to cut out the circle.
- Fold the circle in half, then fold it in half again. You should end up with four pie pieces.
- Cut out one of the pie peices.
- Put the protractor point at the point of the pie piece and line up the 0 degree mark on the protractor with one of the straight edges of the paper.
- Use the pencil to mark off every 10 degrees with a line. Write the number of degrees next to the mark.
- Use the protractor as a ruler and make a line from the point of the paper through each of the degree marks. Make the lines all the way to the bottom curved edge of the paper.
- Tape the straw down one of the straight ends of the paper.
- Tape one end of the string to the point of the paper. Make sure you don’t block the end of the straw.
- Tie the washer to the free end of the string. Make sure the washer hangs somewhere below the curved edge of the paper.
Based on your knowledge of latitude, estimate the location of your home.
Estimation:______________________
Now, on a clear night, take your astrolabe outside and look through the straw at the North Star. Make sure you don’t move it until you check the string to see on which degree mark it aligns itself.
Measured latitude:____________________
Use the globe or a map to find a more exact measurement.
Exact latitude:_______________________
Questions:
1) Do you think one time is enough to measure and estimate your latitude? Why or why not?
2) How do you think measurements can be affected from day to day?
3) Do you think this instrument helped or hindered Columbus during his voyages?
(Optional: The students can also research and support their answers with evidence.)
*Note: I actually purchased a small plastic astrolabe through www.sciencestuff.com (phone #1-800-795-7315) for under $10. It certainly could be a useful model for the students as they construct their own astrolabes.
Top of page