The present invention relates to a planetarium, and more particularly to a planetarium in which planet projectors are driven with by an improved system.
An existing planatarium is constituted to simulate the diurnal motion, annual motion, precessional motion and the latitude adjustment of the fixed stars, Sun, Moon and planets as observed from the earth. To simulate such motions, a pair of star field projectors which project fixed stars of the North spherical heaven and South spherical heaven and respective projectors for projecting the Sun, Moon and respective planets were mounted on a frame in the existing planetarium and this frame was rotated around three axes. Each projector is coupled to the annual motion drive axis provided within the frame through a gear system and thereby each of the projectors moves in conjunction with each other in accordance with the rotation of the annual motion drive axis. The planetarium constituted as explained above is disclosed, for exmple, in U.S. Pat. No. 3,934,358 and U.S. Pat. No. 4,020,568.
However, the above drive mechanism drives respective projectors through the gear systems in interlocking relation and therefore when the projectors are driven so as to move projected celestial bodies from a position at a certain time to a position at another time, the gear systems must be rotated for the simulated time period of such difference, taking a very longer time.
For example, as shown in FIG. 1, in the case of the moving of two celestial bodies located at the positions a.sub.1, b.sub.1 to the positions a.sub.2, b.sub.2, two celestial bodies have to make the annual motions respectively through orbits A, B as much as the difference in time between the both positions. If such annual motion is simulated during 10 seconds/year through the gear system, the annual motions for 1000 years consumes about 2 hours and 47 minutes.
Therefore, it has substantially been impossible to shift a certain celestial body to a very distant time from the present time in the existing planetarium.
Moreover, it has also been impossible in the existing planetarium to simulate a starry sky observed from the Moon or other planets.
The planetariums which have overcome the restrictions on time and space are proposed by U.S. Pat. No. 3,256,619 and U.S. Pat. No. 3,571,954. These patents disclose a structure where the star field projecting portion for projcting the fixed stars in the sky and the projectors for projecting the Sun, Moon and planets are individually driven. Since the planetarium described in these patents does not execute interlocked operations by gear systems, the projected positions of the planets at the present time can be shifted to projected positions of other times or the viewer position can also be shifted to other desired positions. However, these patents do not disclose how the projectors are driven for a change of time or viewer position.