THIS IS HOW YOU MEASURE THE SIZE OF THE EARTH

by Knut Jørgen Røed Ødegaard

Cooperate with a school far away and measure the size of our planet! The method is the same as that used in Egypt almost 2500 years ago (read article).

EQUIPMENT:

• A long tube of cardboard, plastic or metal. It should have a length of 1 - 2 meters and be stiff (it must not bend). A longer pipe may give more accurate answers, but are bothersome. The pipe should not have a large diameter.
• A spirit level
• A square that is easy to read accurately for the angle
• A watch (since you need to do the measurement at a precise time)
• Paper and pencils

Measuring the altitude of the Sun. Illustration: astronomy.no

HOW TO MEASURE: OUTDOOR ACTIVITY (can also be done indoor if the Sun is shining into a class room)

1. Find an even area where you can see the Sun. Use the spirit level to check that the area is absolutely in level.
2. Put one end of the pipe on the ground and lift the other end towards the Sun. Avoid looking at the Sun! You will see a shadow on the ground cast by the pipe. Try to make the shadow as small as possible. When it is completely gone, the sunlight penetrates the pipe.
3. When the sunlight reaches the ground through the pipe, you must keep the pipe absolutely steady. Use the square to measure the angle between the pipe and the ground. When the Sun is exactly in the south (the time for this you or your teacher has already found), you read the angle and make a record of it. Be as accurate as possible!!

You have now measured the altitude of the Sun and may move indoors again!

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