Hale Telescope Dome: Development and Evolution

While progress continued on the design and engineering of (what was to become) the Hale Telescope, preparations were being made to develop the selected Palomar site. Early layout of observatory facilities and Hale dome design emerged from chief architect Russell Porter's Palomar visit in 1935. Porter chose Art Deco as the underlying theme in observatory buildings—presumably influenced by the prevalence of Art Deco architecture in 1930s Los Angeles.

By early 1936 Porter had dome concept sketches and design ideas that he developed in conjunction with the observatory engineering team—particularly lead engineer Mark Serrurier. The dome was to be novel in many ways (e.g. thermal management, monocoque dome design with minimal superstructure—a concept contributed by aerospace engineer Theodore von Kármán). But remarkably the Observatory Council approved an aggressive project plan to begin site preparations and substructure development while design details were still being finalized. There were cosmetic details being reviewed by the Council as late as November 1936. Dome construction began in summer 1936, and by December of that year the separate telescope base and dome substructures were established.

Early 1937 saw rapid advancement on the lower dome structure, but upper rotating dome progress was paced by the placement and surfacing of the dome rotation rails. By mid-year the rail surfacing was complete and the upper dome development could begin—starting with the placement of the “high boom” in late July—a central derrick with articulating boom to manage the heavy dome elements during construction. By late 1937 the upper dome exterior was complete and the dome shutters were in place.

With the new year 1938 came the installation of dome trucks—replacing temporary pedestals supporting the upper dome. By spring the dome drive system was in place and the dome could rotate. Further internal development (upper gantry and crane, internal panels) was complete by fall, and the dome was ready receive the telescope structural elements that began arriving at roughly the same time. Meanwhile the dome exterior was completed and painted.

By late 1941 the dome and telescope structure was complete and ready to receive the 200-inch primary mirror. Following an extended delay due to World War II the primary mirror arrived in late 1947, and the Hale began science operations 18 months later.

No account of the Hale dome development would be complete without mentioning the important human capital of the observatory construction crew. A team of roughly 80 workers and tradespeople (and in some cases their families) lived and worked at Palomar for several years to build the observatory in general and the Hale dome in particular. Led by Construction Superintendent Byron Hill and framed against the backdrop of the Great Depression, many no doubt considered themselves fortunate to be associated with the nationally prominent project. But the observatory was just as fortunate to find so many souls willing to dedicate themselves to realizing the Palomar vision. In curating this digital exhibit we reviewed hundreds of photographs, most contributed by the surviving families of observatory workers who cherished their time at Palomar. Most of the photographs depict ongoing observatory development and important accomplishments and milestones. But many contributed photographs also capture the humanity of the small community living and working together on the observatory grounds.

The Hale dome is largely unchanged since the telescope began science operations in 1949. The finished dome exterior is 137 ft (42 m) in diameter, and the top of the dome is 135 ft (41 m) above ground level: the upper dome surface is roughly spherical centered on the telescope articulation point (the intersection of the two telescope mount rotation axes). The upper rotating dome is roughly 1000 tons (900 tonnes) in mass. The dome shutters open to an unobstructed width of 30 ft (9 m) to allow the telescope to view the night sky. While there have been some modest repairs (e.g. dome rails) and improvements (e.g. HVAC), Porter would consider his stated objective of 'expressing extreme simplicity along with the appearance of permanency' to have been accomplished quite impressively.