36-inch Telescope

The 36-inch Telescope at McDonald Observatory — commonly called “the 0.9-meter” — is a “light bucket.” It was designed to be used with a photometer: an instrument that measures the relative brightness of a star and how that brightness changes over time. The mirror was made to collect as much light as possible, rather than to make detailed images. It was commissioned in the 1950s by the University of Chicago, which ran McDonald Observatory from 1932 to 1962. The telescope was completed in 1956. It was the second telescope to be completed at McDonald.

The rock that forms the dome-wall surrounding the telescope was quarried from the Eppenauer Ranch adjacent to the Observatory. The metal dome was constructed from materials left over from the 1938 construction of the 82-inch Otto Struve Telescope. McDonald Observatory employees built both the dome and the wall. The hydraulic platform floor inside the dome was built from a spare garage lift.

The telescope was used for professional observations for decades. But by the time the Hobby-Eberly Telescope was completed in 1997, the 36-inch was starting to get old and its technology was seriously out of date. Astronomers preferred using larger and more effective telescopes. But rather than let this telescope sit and collect dust, the Observatory had another idea: use it for public and educational programs.

Public Programing on the 36-inch Telescope

Please note: Special viewings and other public programs on the 36-inch Telescope are paused through summer 2026 to allow for important updates and maintenance to preserve the ongoing operations of this historic telescope.

McDonald Observatory hosts a variety of public programs on the 36-inch Telescope. The most popular of these are its Special Viewing Nights, which allow small groups to use the research-grade telescope firsthand. Weather permitting, participants get to see around a dozen objects, ranging from planets, to binary stars and star clusters, to galaxies.

We also offer Special Viewing Nights on the Otto Struve Telescope.

Elderhostel (now Road Scholar) and McDonald Observatory’s teacher professional development programs have also used the 36-inch Telescope for observations.