Magic Mountain – The Engineering of Palomar Observatory

Hale Telescope (Caltech)

Hale Telescope (Caltech)

Time spent around the physical artifacts of discovery – laboratories, museum displays, university offices – can provoke questions about how advances are really made: Who is most responsible for new scientific knowledge?  And who gets the credit?  Is the breakthrough in the mind or in the tool that made it possible?


These were some of my own thoughts during a recent behind-the-scenes tour of Palomar Observatory.  I’d seen the observatory before – it’s a pleasant drive from San Diego – and even visited there once or twice. This day allowed a deeper look, however, which gave time for deeper observation of its details.

Palomar Observatory (Palomar/Caltech)

Palomar Observatory (Palomar/Caltech)

The 28,000 pound mirror of the Hale Telescope required a new kind of truss to support its weight. Precision tracking for the 1.2 million pound scope required advancements in three-dimensional cams and gears. Innovations in bearing systems were developed to allow almost frictionless movement.

The infrastructure engineering of Palomar was essential to its science, and just as groundbreaking.

A vision as big as space
Palomar Observatory, and the 200-inch Hale Telescope, was the Apollo program of its time (funding came in 1928) and, in many ways, it mirrored the space program:

  • The goal was to build a capability better than anything before it – the Hale Telescope was to be twice as big as the 100-inch Mount Wilson telescope
  • The project cost a fortune for its time – $6 million was the largest science project to date
  • It was both famous and controversial – many thought that such money should be spent in other ways, especially after the Great Depression of 1929
  • Designing and building the observatory required new collaborations among scientists, engineers, government, universities, and private companies
  • The program suffered and survived hard times – work on Palomar took 20 years to complete
  • Even after scientific research began in 1949, things didn’t always work as planned

While the observatory is an achievement in science, however, it’s easy to overlook its achievements in technology. Like the Apollo program, gargantuan equipment had to be operated consistently with microscopic precision, and cutting-edge solutions were required.

The 200-inch mirror was at the engineering limits of glass. Many experts said that it couldn’t be built, and they were right; glass castings failed. Engineers turned to Pyrex, a novel material for the purpose, and to honeycombed construction for weight savings. Even that failed on the first try, in front of the public and the press (a portent of the early space program?).  Success came with a second casting, done in private.

A flexible truss, newly-invented by Caltech engineer Mark Serrurier, proved essential to moving the 70-foot telescope across the sky while maintaining its mirror alignment.

Conventional metal bearings couldn’t begin to support the weight of a moving million-pound object, so engineers designed a system of injected high-pressure oil to reduce friction. Ironically, the oil worked too well, forcing them to add a half-horsepower motor to steady movement with controlled friction. The motor was still functioning until recently, when it was replaced by a newer technology.

Hale Telescope mirror (Caltech)

Hale Telescope mirror (Caltech)

The gift that kept on giving
Achievements at the observatory have more than paid off the early investment of money and ingenuity.  Astronomers have used Palomar telescopes, including the 200-inch Hale, to:

  • Discover the nature of quasars – galaxies with supermassive black holes at their centers
  • Study gamma ray bursts, that originate from black holes
  • Discover a new kind of supernova
  • Directly image exoplanets

A less popular achievement among some people was the contribution of Palomar astronomers to the demotion of Pluto as a planet.  Discovery of other similar-sized solar system objects at Palomar eventually took away Pluto’s special status.

Astronomers still vie for access to the Hale Telescope today. Many prefer it to more modern telescopes, owing to its continued optical and engineering precision.

Chicken or egg . .  or both?
So, who deserves the credit for these science discoveries?  The astronomers who used the Palomar telescopes or the engineers who made them? The answer is both obvious and trite, of course, as everyone was essential to the outcome.  The question is worth asking, however, because the tool development that precedes “famous” advances is often no less original or profound, and no less worth of attention.

Big science doesn’t always follow the model of Palomar Observatory.  Far from it.  In an era of science initiated by entrepreneurs and funded by social media campaigns, projects like Palomar are unlikely to be repeated in the future. What remains, however, is that tools will precede discoveries and that toolmakers will be as ingenious as the scientists who use their creations.

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