Such arrangements known under the designation of planetariums, are generally associated with astronomical clocks. It has likewise been suggested to provide such an arrangement on portable timepieces. One of these is described in the Swiss patent No. 627.042. This patent describes a watch including two faces, one of which is provided with means indicating the time of day, the date and the phase of the moon, the other being provided with superposed discs turning around a common axis, each disc bearing the distinctive sign of a planet. The driving means for the discs includes superposed wheels coaxial to such discs with one wheel per disc. It will be readily understood that such an arrangement requires a considerable thickness.
A purpose of this invention is to provide a planetarium having a substantially reduced thickness.
In the arrangement described in Swiss patent No. 627.042, the planets turn around the Sun at an angular velocity equal to their average speed of rotation around the Sun, the frame of reference being defined by the stellar system.
As has been previously mentioned, the indication of the phase of the moon is achieved in this arrangement on the first face of the watch, i.e. that bearing the time indications. However, such an indication forms an integral portion of the astronomical information. This information cannot be associated with the arrangement described without considerably increasing the volume and fundamentally reconsidering the construction since it would be necessary to mount pivotally and drive a lunar disc on the disc bearing the earth indication.
A further purpose of this invention is to obtain a planetarium enabling the display of information associated with the earth and the moon in a reduced volume.
According to a particular feature of the invention the reference system is no longer that of the stellar system, but rather that of the set formed by the Sun and the Earth. In this manner it is possible to complete the planetarium by complementary display elements associated with the movement of the moon around the earth, these elements being pivotally mounted on the support itself.
In a planetarium having dimensions as limited as possible, one may be satisfied to represent only the planets closest to the earth which is the case in the previously cited document or otherwise to represent the most distant planets on circles which are closer to the center than they would be if one employed the same scale as that employed for the closer planets. There results therefrom that the measurement of the angular position of the planets relative to the earth is distorted by a parallax effect.
Another purpose of this invention is to resolve this problem.