A hand-driven tellurium that demonstrates the movement of the Earth around the Sun and of the Moon around the Earth for geography and astronomy lessons.
This tellurium is a mechanical instrument that reproduces the mutual positions of the Sun, the Earth and the Moon in motion, and is used in geography and astronomy classes. When the handle is turned, the globe of the Earth describes a circle around the model of the Sun while rotating around its own axis, and within the same cycle the satellite sphere of the Moon travels around the globe. Thanks to these movements the instrument illustrates the change of day and night, the alternation of the seasons, the solstices and the equinoxes, the polar day and the polar night, the phases of the satellite, and solar and lunar eclipses.
A sphere that plays the role of the Sun is fixed on a stationary stand in the centre of the model, and the boundary of day and night on the globe of the Earth is shown with an external light source directed along the plane of the orbit from the side of the model of the Sun. The axis of the globe is permanently inclined at 23.5 degrees to the perpendicular of the orbital plane, which models the real inclination of the Earth’s axis, and the direction of the axis remains unchanged during the movement, staying parallel to itself. The sphere of the Moon travels around the Earth on a special bracket, changing its visible illuminated part and demonstrating the phases of the Moon. A circular scale on the base is marked with the names of the months for determining the position of the Earth on its orbit; the markings are in Ukrainian.
The drive is manual, by turning a handle, so the teacher chooses the speed of rotation and the point at which the model is stopped for detailed examination; no power source is needed, as both the drive and the demonstration are purely mechanical. The dimensions of the assembled product, length by width by height, are 40 x 20 x 30 cm, and the scale and the moving elements can be read from a distance of several metres, which suits demonstration to a group of students. Materials, the dimensions of the parts and the mass are given in the packing list. The model is intended for geography and astronomy classrooms, is placed on a demonstration table and needs no preliminary assembly. The conditions of use are the premises of an educational institution at an air temperature of +5 to +40 degrees Celsius and relative humidity of 40 to 60 % without condensate. The marking carries the trade mark, the model and a place for an inventory number. The service life is 5 years and the warranty period is 12 months.
The set includes the tellurium assembled, comprising the base with the circular scale, the Sun unit and the rod-bracket with the globe of the Earth and the sphere of the Moon – 1 pc, a passport with a warranty card – 1 pc, and individual transport packaging – 1 pc. The exact composition of the set is given in the packing list, and the factory packaging is worth keeping for storing the model during the holidays and for transport.
The model is placed on a separate table in the centre of the classroom, with free space around it, because the rod describes a circle during rotation and part of the phenomena is visible only from a certain direction. The prepared light source, a table lamp without a shade or another directional lamp, is placed on the side of the model of the Sun with its beam along the plane of the orbit onto the globe of the Earth, and the classroom is darkened, since without darkening the boundary of light and shade on the globe and on the sphere of the Moon is indistinct. The handle is turned smoothly, without jerks, and only in the working direction, anticlockwise when the model is viewed from above; the Earth is brought to the mark of the required month on the circular scale, and the model is stopped in this position to give the students time to examine it. The demonstrations are shown in turn – first the daily rotation alone, then the annual movement, then the monthly revolution of the Moon.
Preparation and demonstration are carried out by the teacher, and students observe under supervision. Fingers are kept away from the gear transmission and the hinged joints of the bracket while the model is moving, and the model is carried by the base with both hands rather than by the rod, the globe or the bracket. The model is wiped with a soft dry or slightly damp cloth, the globe and the sphere of the Moon gently, so as not to damage the applied image, and dust is removed from under the gears with a dry brush; the model is not immersed in water or washed under a tap, is not lubricated by the user and is not disassembled. It is stored in a dry heated room at +5 to +40 degrees Celsius and relative humidity of 80 % without condensation, covered from dust and protected from direct sunlight, heating appliances, impacts and vibration.
