Visitors to the Staerkel Planetarium are introduced to “Carl” when they walk in the dome. Some people mistake Carl for a telescope in an observatory, but Carl puts “stars” on the dome instead of collecting light from stars.
“Carl” is the Carl Zeiss Model M 1015 star projector, an intricate piece of machinery that has been at Parkland College since the planetarium opened 35 years ago.
Mechanical star projectors were first produced in Germany almost 100 years ago, but few are used today because most planetariums now use digital projectors. Many people are nostalgic for mechanical projectors because they still produce more realistic stars on a dome. Although the Staerkel Planetarium installed a digital system in 2010, the Zeiss is still in place because it is mounted on an elevator, allowing it to avoid blocking the digital images.
Mechanical star projectors are complex systems of gears, lights, switches and image plates. The two “starballs” on each end of the column can project 7500 stars, which is roughly the number of stars that are visible to the naked eye under a perfectly dark sky.
However, the Zeiss doesn’t show them all at once. It only displays stars that are above the horizon, and its diurnal motor turns to have the stars rise and set just as Earth’s daily spin makes them appear to move across the sky.
The Zeiss can show the sun, moon and visible planets. Uranus, Neptune and smaller bodies were excluded because they can’t be seen without a telescope. The projector has an annual motor to accurately show their changing positions as the moon orbits Earth and the planets orbit the sun.
From our perspective on Earth, the sun appears to move on a line called the ecliptic through the Zodiac constellations. The Zeiss can display the ecliptic, and the sun’s position is the only way the staff can be certain about the date of the sky on the machine!
The projector shows other lines to help operators keep track of celestial coordinates and to help set the location. By adjusting the latitude, one can see how the sky moves at the poles and how stars in the Big Dipper usually stay below the horizon in the Southern Hemisphere.
The Staerkel Planetarium will celebrate the 35th anniversary of its dedication at 2 p.m. Oct. 1. The retired director of the planetarium, Dave Leake, will present “Staerkel Unplugged: The Zeiss-Only Experience,” a show where the digital projectors will be off and a public audience will be immersed in the sky produced by this classic system for the first time since 2010.
The William M. Staerkel Planetarium at Parkland College offers sky tours, full-dome videos, sensory-friendly programs, shows in Spanish, Pink Floyd light shows and spacesuit shows. Find the public show schedule at parkland.edu/planetarium. Contact the staff at firstname.lastname@example.org to book a show or to rent a telescope.
The Champaign County Museums Network has information at champaign