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CSIRO's Double Helix Science Club "Is the World Flat?" Activity

The "Is the world flat?" activity was carried out Australia-wide by CSIRO's Double Helix Science Club members as a lead-up to the 1999 Queensland Astronomy Education Conference. The instructions was provided in the February 1999 issue of the The Helix magazine.

A rough draft (pre-publication) of the article is provided below.

Ever wondered how the ancients worked out that the world is round? After all, try looking out the window, the Earth looks pretty flat! The answer came when a Greek guy named Eratosthenes noticed that in his home town Alexandria, at midday at a certain time of the year the Sun’s rays cast a shadow, while at Syene several hundred kilometers to the South, it didn’t. This meant that the Sun appeared at a different altitude (or height above the horizon) at each location. Eratosthenes’s great leap of logic over 2,000 years ago was to realise that the easiest way to explain this difference was to assume that the world was round which would affect the apparent height of the Sun above the horizon. Otherwise if the Earth was flat, the shadow would appear the same length on all part’s of the Earth’s surface.

The Convenor’s of the 1999 Queensland Astronomy Education Conference have organised an opportunity for you to recreate this discovery with the help of other Double Helix Club members across Australia. All you need to do is make the astrolabe, shown, measure the altitude of the Sun (as shown in the diagramme) at the correct time for your State and then post the observation to the address given below. The measurements will be listed for each State, at the Mobile Planetarium Service Homepage for you to compare. If Eratosthenes was right and the Earth is not flat, then the measurements sent in by CSIRO's Double Helix Club members across Australia will be different.

A master of the astrolabe can be copied for printing from the Mobile Planetarium Service Homepage at http://www.ozemail.com.au/~ssemps. To find it, click on the link for the Queensland Astronomy Education Conference ’99 and select the Activities link. The only other equipment you need is a short piece of string, a piece of sticky tape and a washer to weight the piece of string down. You may wish to glue the astrolabe outline to a piece of thin cardboard to make it more rigid.

Note that the astrolabe is designed for you to measure the altitude of the Sun without looking at the Sun. All you need to do is hold the completed astrolabe in a vertical position so the string hangs freely. Then without looking at the Sun, point the arrow towards the Sun. Ensure the arrow is pointing straight at the Sun by making the shadow from part A cover all of part B. The altitude of the Sun will be the number underneath the string. Double Helix Club members in Queensland, New South Wales, Victoria and Tasmania should measure the altitude of the Sun at 12 Noon on Sunday the14th of February. South Australian and Northern Territory members should conduct the measurement at 11.30am and Western Australian members at 10am. Note that the times are different to allow for time zone differences.

Once you have made your measurement, write the following details on the back of an envelope (your first name, your city and suburb (if relevant), your State and the measurement in degrees) and post to: "What shape is the World?" Activity, c/o Mobile Planetarium Service, Southern Star Education, 96 Doncaster Drive, Beechmont, QLD 4211. Then visit the Mobile Planetarium Service Homepage at the link given above after April 9th 1999 to see what the results are. Was Eratosthenes right?