The McKeldin Planetarium
View of the McKeldin Planetarium looking toward McDowell Hall on the Annapolis Campus.
The McKeldin Planetarium used a Spitz A-2 projector from its completion in 1961 until the spring of 2010. The projector was installed in the 24 foot diameter dome in 1961. With the original Spitz A-2 projector, we were able to show the "Motion of the Same," i.e., the daily motion of the sky about the polar axis, and could demonstrate the "Motion of the Other" using the projection of the Sun, which has an independent motion with this projector. Perhaps one of the most striking parts of the class demonstrations using the original projector is the illustration of the path that individual stars take about the polar axis. They are perfect circles. This more than anything else shows why Ptolemy begins the construction of his system with circles. They are the most manifest elements of the motions that he observes.
In addition to these parts of the demonstration, we were able to use the old projector to project the Celestial Equator, the Ecliptic, and the Celestial coordinate system on the sky. This illustration of Right Ascension and Declination and the Ecliptic gives students a good intuition of the system Ptolemy uses to specify the motions that he sees. We use this coordinate system to the present day.
The new projector for the McKeldin Planetarium uses a Panasonic PTAE 4000 1080p digital home theater projector with a specially designed stack of two chromatically corrected lens assemblies. This design allows us to paint the entire dome with a geometrically corrected image of the whole sky from horizon to horizon. This assembly, along with portable heating and air conditioning units, was a gift of the St. John's College Graduating Class of 2010. The projector and lens assembly provide a reasonable image in terms of resolution and chromatic correction.