Since its opening in 1973, the SFSU planetarium has been in continuous operation for a wide range of educational and outreach activities. Over its more than 40 year history, it has served an estimated 40,000 SFSU students, 50,000 school children, and more than 10,000 members of the public. Numerous SFSU graduate and undergraduate students have gained experience teaching and communicating about science in this space. Many are now educators in science museums, planetariums, universities, community colleges and high schools around the Bay Area and beyond.

Charles F. Hagar was a professor in Department of Physics and Astronomy at SFSU from 1959 to 1994, and continued to teach at SFSU for ten years after his retirement. He designed all the astronomy-related facilities in Thornton Hall, including the planetarium and the observatory. The planetarium was named for Professor Hagar upon his retirement.

The Charles F. Hagar planetarium dome is 26.5 ft (8.1 meters) in diameter, takes up two floors in Thornton Hall, and seats 45 visitors in three concentric circles. The planetarium houses a Spitz Space systems 512 projector that displays 1,354 stars on the dome, along with the Sun, Moon, and planets. The Spitz, which was state-of-the-art at the time it was installed, also projects the celestial equator, the ecliptic, the meridian, and several constellation figures.