The McKeldin Planetarium

View of the McKeldin Planetarium looking toward McDowell Hall on the Annapolis Campus.

The Original Spitz A-2 Planetarium Projector

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.

About the new McKeldin Planetarium projector

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.

The projector is mounted to shine vertically and illuminate the center of the Planetarium dome. The projector is driven by an Linux-based (Ubuntu) computer running the Stellarium 0.10.2 planetarium program.

In addition, to "paint" the entire dome, the Panasonic 1080p shines this image of the sky through two concatenated lens assemblies. The first lens is a Raynox Digital CF185 Pro circular fish-eye conversion lens. This chromatically corrected lens is designed to provide a 185 degree field-of-view (FoV) for single lense reflex (SLR) and digital video cameras. However, this lens does not provide a full dome projection when used with the PTAE 4000 projector. We have therefore adapted this lens to our purposes by using a Raynox MX-3000 Pro Semi-Fisheye (0.3 x) chromatically corrected lens mounted on top of the CF185 Pro lens by means of a machined, aluminium adaptor shown in the pictures above. This assembly therefore provides a full dome projection with a dynamic range, flexibility, and resolution much greater than the original Spitz A-2 system.

We also do a fair amount of work during these classes to teach students to recognize the constellations as they progress through the months of the academic year. This is reinforced by the star gazing at the St. John's College Observatory. These observing sessions are held after seminars nearly every week throughout the academic year (weather permitting).

The McKeldin Planetarium and the St. John's College Observatory at St. John's College are open to the general public and to interested groups on an occasional basis.

For those interested in the assembly and dimensions of the lens adapter rings that we use, we hope that this link is helpful: