Read Online The Perfect Machine by Ronald Florence - Free Book Online
Authors: Ronald Florence
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observatory of-20°F, Hale attracted extraordinary optical and astronomical talent to Yerkes. For a period he could boast having the best observers and the best glass grinders in the world together under the domes and in the laboratories. Those who had seen the toll the construction took on George Hale urged him to settle down to the promising career of director of the great observatory. But even before Yerkes was dedicated, George Hale had a new idea.
In his own studies, with solar telescopes, Hale used a spectrograph to study the chemical composition of the sun. By identifying lines in the spectrogram that corresponded to the emission or absorption of particular materials, he could identify the presence of various elements in the sun—almost as accurately as if he had a sample of solar material in a laboratory. Knowing the chemical composition of the sunand the solar atmosphere, astronomers could begin to ask what chemical or atomic processes were at work to create energy and light. What, Hale asked, if the same techniques that he applied to the sun could be applied to distant stars? It would be a whole new field, astrophysics, a discipline devoted to trying to determine what the stars and other celestial bodies outside our solar system were made of and what processes created the enormous energy in them. Once astronomers and physicists made some headway on those questions, they could take on the even grander field of cosmology, which tried to understand how the universe was put together, to discern the size, shape, structure, and origin of the cosmos.
The answers to those questions would demand telescopes far more powerful than even the great Lick and Yerkes instruments. Hale’s new dream was a huge new telescope, somewhere out in the clear air of California, where cloudless mountaintop skies provided night after night of good seeing, and where a facility could be all but immune to light pollution from urban illumination. The telescope Hale had in mind would not only be even bigger than the great Yerkes, but it would turn the circle from refractors, like the Lick and Yerkes telescopes, back to reflectors, like the telescope Newton had once used, relying on a mirror instead of a lens to gather and focus the faint light from distant objects.
The technology of refractors was temporarily exhausted. It might have been possible to cast and grind larger glass lenses than the forty-inch-diameter disks in the Yerkes refractor, but the sheer weight and fragility of the enormous glass disks, which can be supported only at the edges, and the engineering of the long tube, which must rigidly hold and point the lenses, had reached their limits. In France a refractor with lenses close to sixty inches in diameter was built and displayed at the Paris Exhibition of 1900, but it was not successful as a telescope. Even if a bigger refractor could be built, a reflector had many arguments in its favor for astrophysics research.
The light of a star or other distant object goes through the objective lens of a refractor. Because light of various colors bends, or refracts, differently as it goes through the glass, a refractor is not achromatic; the lens forms a series of images of different wavelengths. Only some of these effects can be corrected. A reflector, by using the surface of a mirror to focus the light, avoids this problem. The optics of a big reflector are also easier to grind and polish. Instead of four surfaces of glass to grind, figure, and polish, two on each of the elements that are sandwiched to make up an objective lens, a reflector requires only a single optical surface, the face of the primary mirror.
Finally, the physical mounting of a refractor, with its long, rigid tube supporting the objective lens at one end and an eyepiece or instrument at the other, presents difficult engineering problems as the instrument gets larger. The long tube must be balanced on its equatorialmounting, and for the telescope to reach all areas of
In his own studies, with solar telescopes, Hale used a spectrograph to study the chemical composition of the sun. By identifying lines in the spectrogram that corresponded to the emission or absorption of particular materials, he could identify the presence of various elements in the sun—almost as accurately as if he had a sample of solar material in a laboratory. Knowing the chemical composition of the sunand the solar atmosphere, astronomers could begin to ask what chemical or atomic processes were at work to create energy and light. What, Hale asked, if the same techniques that he applied to the sun could be applied to distant stars? It would be a whole new field, astrophysics, a discipline devoted to trying to determine what the stars and other celestial bodies outside our solar system were made of and what processes created the enormous energy in them. Once astronomers and physicists made some headway on those questions, they could take on the even grander field of cosmology, which tried to understand how the universe was put together, to discern the size, shape, structure, and origin of the cosmos.
The answers to those questions would demand telescopes far more powerful than even the great Lick and Yerkes instruments. Hale’s new dream was a huge new telescope, somewhere out in the clear air of California, where cloudless mountaintop skies provided night after night of good seeing, and where a facility could be all but immune to light pollution from urban illumination. The telescope Hale had in mind would not only be even bigger than the great Yerkes, but it would turn the circle from refractors, like the Lick and Yerkes telescopes, back to reflectors, like the telescope Newton had once used, relying on a mirror instead of a lens to gather and focus the faint light from distant objects.
The technology of refractors was temporarily exhausted. It might have been possible to cast and grind larger glass lenses than the forty-inch-diameter disks in the Yerkes refractor, but the sheer weight and fragility of the enormous glass disks, which can be supported only at the edges, and the engineering of the long tube, which must rigidly hold and point the lenses, had reached their limits. In France a refractor with lenses close to sixty inches in diameter was built and displayed at the Paris Exhibition of 1900, but it was not successful as a telescope. Even if a bigger refractor could be built, a reflector had many arguments in its favor for astrophysics research.
The light of a star or other distant object goes through the objective lens of a refractor. Because light of various colors bends, or refracts, differently as it goes through the glass, a refractor is not achromatic; the lens forms a series of images of different wavelengths. Only some of these effects can be corrected. A reflector, by using the surface of a mirror to focus the light, avoids this problem. The optics of a big reflector are also easier to grind and polish. Instead of four surfaces of glass to grind, figure, and polish, two on each of the elements that are sandwiched to make up an objective lens, a reflector requires only a single optical surface, the face of the primary mirror.
Finally, the physical mounting of a refractor, with its long, rigid tube supporting the objective lens at one end and an eyepiece or instrument at the other, presents difficult engineering problems as the instrument gets larger. The long tube must be balanced on its equatorialmounting, and for the telescope to reach all areas of
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