Solar System

Make an Astrolabe

What it does

Early mapmakers used a tool called an astrolabe to measure latitude. This experiment lets you make an astrolabe of your own.

What you need

• Drinking straw
• Protractor
• Masking tape
• String
• Metal bolt or other small weight
• Ruler
• Another person to help

What to do

1. Cut a 12-inch piece of string.
2. Tie the metal weight to one end of the string.
3. Tie the other end of the string to the center of the protractor, on the straight edge.
4. Tape the straw along the straight edge of the protractor.
5. Hold the astrolabe so that the straw is at the top, and the string hangs down beneath.
6. Look through the straw at the tops of distant objects, and have your helper record the angle of the hanging string.

What it's all about

You have to tilt the astrolabe to look at the tops of distant objects, but the string continues to hang straight down to the ground because of gravity. As you tilt the protractor to different levels, the string hangs at different angles in relation to the straw.

Latitude is determined by measuring the angle from the horizon to the North Star. Early mapmakers used the astrolabe to do this. If you were at the North Pole, you would have to point your astrolabe straight up to see the North Star. If you were at the equator, your astrolabe would be parallel to the ground.

Remember, be sure you have a parent, teacher, or other adult help you!

Learn more about how maps are made!
Read about it.