Patent ID: 7887194

Claim:
A simplified planetarium apparatus comprising: a light source; a light converging optical system that converges light from the light source; a diaphragm having a window configured to pass the converged light, a center of the window being arranged correspondingly to a zenith of the sky; a rotation mechanism configured to rotate a replaceably mounted stellar base plate having a pattern of holes transparent to the light from said light source and arranged correspondingly to stars, a rotation axis of the stellar base plate being arranged correspondingly toward a celestial pole; a projection system configured to project an image of a portion of the stellar base plate corresponding to said window; and a sliding mechanism configured to change the distance of the rotation axis of the stellar base plate from an optical axis within an area of said window, wherein the rotation axis and the optical axis are both positioned within the window and arranged in parallel with, and spacedly from, one another so that portions of the stellar base plate exposed to the window move as the stellar base plate rotates while portions of the stellar base plate around the center portion remain exposed to the window, whereby a simulated diurnal motion of stars rotating around the celestial pole is projected from the projection system at a latitude corresponding to the distance.