Abstract: An ellipse is rotated in such a way that the time interval which elapses between the successive passages of the major axis of the ellipse and the minor axis of the ellipse through the same position corresponds to the time interval which elapses between a successive high tide and low tide. The ellipse is rotated substantially in phase with the lunar cycle.

Abstract: An apparatus for viewing a representation of the celestial vault including a tube bearing a ring of graduations that indicate the dates of the days of a year, and a tube bearing a ring of graduations that indicate the hours of a day. The tubes are axially aligned and rotatable with respect to each other about the axis. One tube contains a representation of the night sky, and the other contains an element, such as a lens, for viewing the representation. The tubes are separably joined so that they can be disassembled, each tube rotated end-over-end through 180.degree., and the tubes reassembled. In one condition of assembly, a sky representation of the northern hemisphere is used, and in the other condition of assembly, a sky representation of the southern hemisphere is used.

Abstract: An apparatus for reproducing the appearance of heavenly bodies including a cover having an opaque wall defining a substantially circular opening, and a disc-like or spherical part representative of a heavenly body sized to substantially fill the opening in the cover. The part and cover are relatively rotatable about an axis which passes through the center of the opening in the cover and along a diameter of the part. The opaque wall of the cover may be hemispherical, planar, or tubular. The part may represent the moon or a celestial vault. The apparatus may include a base which supports the cover and part and houses a mechanism for rotating one of the cover and part with respect to the other.