Otto Struve Telescope

The Otto Struve Telescope, the first major instrument built at McDonald Observatory on Mount Locke in West Texas, opened in 1939 with the world’s second-largest mirror. Its location in the Davis Mountains offered clear, dry air and favorable elevation, helping make the observatory a leading astronomical site, especially as competing large-telescope projects slowed during the early 1940s. Built between 1933 and 1939, it was renamed in 1966 for former observatory director Otto Struve, who helped shape its early scientific work. The telescope contributed to the Johnson-Morgan UBV photometric system, was used in the 1949 discovery of Neptune’s moon Nereid, and remains active with modern upgrades.

Texas · United States