First artificial starry sky in Jena

Master's student Sabrina Engert on the first projection planetarium from the Carl-Zeiss company

In the summer of 1923, the first artificial starry sky shone in Jena. Ten years passed from the idea to the construction. There, mechanics, engineers, astronomers and physicists had worked on a special device with which the fixed starry sky could be shown. What was the groundbreaking idea?

Engert: First of all, the circumstances why this work was started: There had been mechanical planetariums for a long time, but they could only convey the dimensions of the solar system to a limited extent. Even mechanical planetariums that filled an entire room had difficulty conveying a lifelike impression of the universe. Here's an example: If the Earth were the size of a piece of candy and we wanted to represent the distance to the Sun true to scale, then the Sun would be about 180 meters away. If we then take the same scale for the outermost planet, Neptune, which is at a distance of about 4,687,000,000 kilometers from the Earth, Neptune would be about 5.7 kilometers away. This means 31.88 times the distance that the Sun and Earth are from each other, showing the difficulty of representing a scale model of the solar system alone. So Oskar von Miller, director of the Deutsches Museum in Munich, commissioned the idea at the time from Carl-Zeiss, the company primarily involved in optics. He already had the idea of a projection planetarium to overcome these very limitations, but needed help. In 1919, therefore, the idea was put forward by Dr. Walter Bauersfeld, a member of the Carl-Zeiss management. For this purpose, small projectors were to project the stars and planets onto a spherical wall in order to "imitate" the sky, so to speak.

On October 21, 1923, in preparation for the first German planetarium in Munich, the first artificial starry sky was demonstrated on site with an unprecedented projection. This was the beginning of the success story of the projection planetarium, which started regular operation in 1925. What can you show in such a projection, for example?

Engert: You could almost say that the success story began in the spring of 1923, when a first demonstration of the new technology took place in a temporary dome on the roof of Carl-Zeiss in Jena. News of the new sensation spread quickly. So even the mayor of Barmen at the time, Dr. Paul Hartmann, decided to see it for himself on site. In his speech at the opening of the Barmer Planetarium, he called it a "marvel of German technology. The projections today can show incredible things. Visitors to a planetarium can virtually travel through entire galaxies and leave our Milky Way. They can see different constellations and marvel at every planet in our solar system from the comfort of a chair. But the first projection apparatuses also showed amazing images of stars, the Milky Way and various constellations.

The Zeiss company from Jena received the order to build the Copernican Planetarium in Munich. Sometimes, however, people talk about Ptolemaic planetariums. What is the difference?

Engert: Essentially, these designations mark from which "point of view" the universe is viewed. Copernican planetariums owe their name to the idea of the heliocentric view of the world, i.e., the idea that the sun, not the earth, is at the center of the universe. When I enter a Copernican planetarium, I see just that, the sun and the planets in elliptical orbits around it. There is a huge Copernican planetarium in the German Museum in Munich. There I see the sun in the center and all planets orbiting around it. But this does not mean that a Ptolemaic planetarium has the earth in the center. There it concerns again the point of view, from which I regard that. However, if I am sitting or lying in a chair and looking up at the dome from my vantage point, then I am seeing the universe from the Earth, so to speak. It is quite important to emphasize that although today's optical planetariums are called Ptolemaic because we see everything from the Earth, so to speak, optical planetariums definitely follow the scientific standards and thus the heliocentric doctrine. So synonyms for the division into Copernican and Ptolemaic are heliocentric and geocentric.

How many stars can such a projector display?

Engert: The planetarium in Bochum, for example, has the Universairum IX model and speaks of 9,000 stars that the projector casts onto the dome. But besides the stars, the projectors also show the Milky Way, nebulae, galaxies, planets and so on.

After completion, the device was permanently installed in the German Museum in Munich as Model I in 1925. In the meantime one has arrived at model IX. In the course of digitalization, fiber optics can be used today to image the night sky just perfectly. For people from Wuppertal, the Zeiss Planetarium in Bochum is the easiest to reach. Have you ever been there?

Engert: Yes, very often. I've even seen some shows several times, simply because there's so much to learn and you also see the dimensions of the universe outside the Milky Way. For example, one program is called 'From the Big Bang to Humans` and it is very interesting because you can see visually how humans have evolved. There are even astronomy shows for children. Among others, the program "Fascinating Space" is recommended. By the way, the Galileum in Solingen, an observatory that is now a planetarium, has also been around for a few years and offers a wide range of events.

Uwe Blass Sabrina Engert works as a research assistant in the History of Science and Technology at the Faculty of Humanities and Cultural Studies at Bergische Universität.