Irma Hannula

EAAE Summer School Working Group (Finland)


The angle between the axis of the Earth and the plane of the orbit is approximately constant. Instead of that, the orientation of the axis is chancing. The axis seems to go along the surface of the cone. Hipparchus discovered this motion, called precession, over two thousands years ago. The movement of the axis is very slow, one cannot see any change in the period of few years or decades, but compared with observations made thousands of years ago, the change of the location is remarkable.

In this workshop we will construct a model, which help us to percept the movement of the North Pole in the night sky. We start by calculating the coordinates of the most famous points in time. Then the scale in the sky map has to be determined. After drawing the coordinates of the test points, we can determine the central point of the circle of North Pole’s path. Then we draw the circle. It is interesting to look for some dates and realise on which constellation the pole is at that time.

With this new model, we can demonstrate the precession of the Earth’s axis. A wooden or plastic ball may represent the Earth, and a grill stick represents the axis. Small pieces of iron or other heavy material can be fixed in the area of the equator. Then we will try to put the Earth in the rotating motion, like a gyroscope.

Full version (PDF).


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