Marie Drake Planetarium

Where the stars always shine in Juneau, Alaska

Our Spitz Star Projector turns 50

Click here for article on this anniversary.

Art Shaw with our projector 

Spitz Star Projector

The main instrument in the planetarium is the star projector. The Marie Drake Planetarium is equipped with a Spitz Model A3P. The star projector provides a realistic view of the night sky as seen by the naked eye. It projects stars, planets, Sun, and Moon in their correct positions as well as an astronomical grid to illustrate the coordinates used by astronomical charts.

The planetarium cost about $70,000 when it was purchased. It is in working condition despite its age. The SPITZ is a hollow metal bulb with over 1400 holes drilled in it. Each represents a star in the night sky. The brighter star requires a lens to focus the light. The cells that hold the lens over the holes are visible as dark rings on the star projector. Some lens have colored gel to simulate star color. Other holes are covered with small film of images of nebular objects and which collectively project the pattern of the Milky Way Galaxy. The bulb that provides the stars is a 75 watt xenon arc lamp projecting 1,400 holes. This is how the solar system is simulated on the 30 foot dome.

The meridian projector projects a line marked off from 0 to 90 degrees from the north point on the horizon, through zenith and down to the southern point on the horizon. The meridian projector allows the planetarium to illustrate how high or low a position(star, planet, etc.) is on the dome from the horizon. The meridian also splits the sky into an eastern and western half. When the sun is directly on the meridian, the time of day of called noon. When the sun is east of the meridian the time of day is called ante meridian(a.m.). When the sun is west
of the meridian, the time of day is post meridian (p.m.).

The ecliptic projector displays the path that the sun appears to travel across the sky. This is very useful for illustrating seasonal markers.  The coordinate projector displays a partial Earth equatorial coordinate system on the dome. The vertical (similar to longitude) are lines of right ascension. The horizontal lines (latitude) are circles of declination. Astronomical charts use these right ascension and declination marks to track the position of stars,
planets, and the Moon in the night sky.