Build your own astrolabe

In this activity students will understand that the Moon, Sun, and other stars appear to move relative to the Earth and that these movements correspond to the pattern of day and night and the seasons.

What you need:

• 30cm ruler or wooden stick
• protractor
• 10cm of string
• small fishing weight
• sticky tape.

What to do

• Fasten the protractor to the ruler using sticky tape.
• Tie the weight to the end of the string and stick the other end of the string to the centre base of the protractor.
• Look across the top of the ruler toward distant objects.

• The string on the protractor will indicate the angle of elevation of the object.

Background knowledge

You can use the astrolabe to measure the angle of the Moon above the horizon at different times of the day or night. You can also measure the angle of different stars above the horizon and see how this changes from month to month. Astronomy websites, books, and the media will tell you where to look for events in the night sky like comets and stars.

Early navigators used similar instruments to navigate across land and sea. They used star sightings each day to check they were travelling in the right direction. One instrument they used is called a sextant. These days we have very accurate navigational tools such as GPS (Global Positioning System) satellite readings. These are accurate up to 22 metres.

Focus questions

• Why would you want to know the angle of the Moon or stars above the horizon? What does this information tell you?
• Who would use this instrument or other equipment like it?