In addition to painting, astronomy became Jac For’s second greatest passion. He regularly attended lectures on astronomy and astrophysics in Munich. Jac For often sat for hours in a private observatory in the heart of Munich in order to observe celestial phenomena.
Jac For searched for and found ways to combine his steadily growing knowledge of astronomy and his pictographic space visions with his painting. From 1959 on, he turned his attention more and more to the depiction of cosmic events.

At the time of their creation, many of his paintings were ahead of their time; they were often beyond what was optically discernible at that time. After the introduction of the Hubble telescope (around 1990) increasingly highly defined and exciting views of cosmic events were made possible. Jac For repeatedly found startling similarities between them and his own ”inner” pictures.
> As he said himself, he was torn between the accurate representation of astronomical findings and his artistic fantasy and swayed back and forth between eyepiece and canvas. In the exciting contrast between art and science, between exact observations and intuitive sensibility, he endeavoured to convey the infinity and beauty of the universe to the observer and make the observer aware of their divine origin.