Cristina Palici di Suni1, Ederlinda Viñuales2

1Interuniversity Specialization School (SIS), Torino (Italy)

2University of Zaragoza (Spain)


The theory of Earth moving around the Sun had, in Galileo age, serious problems. One of these was that, if the Earth is moving, you could observe stellar parallax: you could observe different positions of “nearer” celestial bodies against the far away stars. And this was not verified. No parallax? Then, no heliocentric theory! This sentence is similar to the famous advertising: “No Martini? No party!” Scientific proposals must be supported with experimental observations (soon or late). Galileo explained why parallax was not visible: because of big distances among celestial bodies and angular resolution. The Universe was bigger than assumed by Galileo contemporary people and celestial bodies too far from the Earth for technological tools of 1600.

We wish to understand, in this very practical workshop, the problem of distance, angular size and error with angular distances. Parallax has been a tool to investigate the Universe for ancient astronomers but it is limited by the resolution of angles.

In the first part of the workshop we wish to practice with angular sizes measurements with a simple device hand made. In the second activity we measure the height of a tower, a building (at known distances)… using one eye and a stick. In the third one we measure the diameter of the Sun using tubes and aluminium foils with a pin hole.

Perhaps at the end of the activity young students appreciate better math, trigonometry or simple geometric assumptions because they amuse themselves with sticks and viewers!

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