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- Photographs of Nebulae and Clusters Made with the Crossley Reflector.
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- [Heliogravure plates in Photographs of nebulae and clusters made with the Crossley reflector].
A Arthur de Carle Sowerby Correspondence. Held Collection of Rare Books. Larry Richards Architectural Drawings Collection. Materials Related to Through Shen-Kan. Papers of Sterling and Francine Clark. Tadao Ando Architectural Drawings Collection. Venice Biennale Ephemera Collection. Venice Biennale on the Web. Shannon, superintendent of state printing, ]. Keeler, James Edward, Although Perrine continued to use the Crossley with good results, he was dissatisfied with its performance and operation.
Perrine was determined to improve the telescope and in the years from to , oversaw a reconstruction of the telescope, which brought it into its modern form.
Perrine replaced Common's original tube and mount with a much more rigid closed tube on an English equatorial mounting. The Newtonian flat mirror, which brought the light out to a focus at the side of the tube, was removed and, in its place, Perrine introduced a plateholder directly at the prime focus of the telescope in the middle of the upper end of the tube.
Perrine also introduced a system of prisms and transfer lens so that the observer could "guide" or accurately follow the motion of the stars during the exposure from an eyepiece just outside of the tube.
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With these modifications, the Crossley became a faster and more efficient telescope for photographing nebulae and star fields. The Crossley remained unchanged until when the large inch mirror was coated with aluminum, thus increasing its light-gathering capacity. In the early s, the drive mechanism of the telescope was replaced. The polar axis was turned end for end so that a worm gear could now be used to drive the telescope from the south polar axle housing, and an electronic clock replaced the old mechanical clock.
In the late s Selsyn telescope-position readouts were installed at the observing end of the instrument, and the observer's platform was enlarged and strengthened to carry the additional electronic equipment required by modern observational techniques. A large bearing was installed to ease rotation of the top section of the tube. Finally, a modern darkroom was built.
The Crossley inch reflector is found a few hundred yards southwest of the Main Observatory Building of the Lick Observatory and is still in use as an operational scientific instrument for the study of the stars and galaxies. The Crossley inch reflector at the Lick Observatory was the first of a long line of metal-film-on-glass modern reflecting telescopes that have dominated major astronomical advances for the past century.
In addition, the Crossley has produced more scientific results than any other telescope of its size, including several historically important studies in stellar evolution, the structure and spectra of planetary nebulae, and the discovery and spectral analysis of faint variable stars in young clusters. The Crossley also contributed to studies that confirmed the expansion of the universe.
The Crossley inch reflecting telescope, at the Lick Observatory, marked the first modern application of a reflecting telescope to astronomical studies. In Sir William-Herschel built a reflecting telescope with a inch polished mirror, but the telescope was difficult to point and the mirror needed constant polishing. Shortly thereafter, the two-component lens was developed and refractors became the telescope of choice. Despite the many advantages of reflectors over refractors, it was not until , when the technique of making concave silver-surfaced glass mirrors was perfected, that reflectors again assumed importance in astronomy.
One of the earliest such telescopes was the inch reflector built by British amateur astronomer Andrew Common.
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Common's telescope was built around a inch silver-on-glass mirror that was mounted on an equatorial fork and used as a photographic telescope. The chief innovations in Common's telescope were the achievement of a smooth drive by relieving the bearings of almost the entire weight of the telescope, and the invention of an adjustable plate holder. The bearing load was diminished by submerging a hollow steel float in mercury, while the plateholder had an eyepiece and crosswire attached so that a star just off the edge of the plate could be watched and, if it drifted away from its starting position, be brought back by moving the plateholder.
The end result showed that it was possible to build a telescope that was sufficiently smoothly and accurately enough driven to allow very good photographs to be taken. The last of these conditions was a suitable location for the erection of the telescope. In Common sold his inch reflecting telescope to Edward Crossley of Halifax, Yorkshire, England, who donated the telescope to the Lick Observatory shortly after his retirement from astronomy in Crossley's donation of his telescope to Lick was fortuitous.
For the first time a large reflecting telescope was located on a suitable mountain site where its large aperture could be used to its fullest advantage. Within a short time the Crossley reflector was put to good use when James E. Keeler initiated a program of nebular photography with it. Keeler's photographs showed the existence of hundreds of spiral nebulae that are now known as galaxies. Neither Keeler nor anyone else at the time realized that nebulae were predominantly extragalatic, but Keeler, using Crossley photographs, was the first to realize that these objects were a major constituent of the universe.
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After Keeler's death, astronomer C. Perrine completed Keeler's observational program, and in published a remarkable selection of Crossley photographs in memory of Keeler. Keeler's and Perrine's success with the Crossley reflector was probably more influential than any other single factor in convincing professional astronomers of the practical effectiveness of large reflectors. By the early s, as a result of Keeler's and Perrine's work with the Crossley, it was apparent that the future of large telescopes lay with mirrors rather than lenses.
A few years later, when George Ellery Hale began to plan for the establishment of a large observatory on Mount Wilson in California, the use of a large refracting telescope was not even considered. The Crossley had shown the way to the future of astronomy.
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Large reflecting telescopes would now dominate 20th-century astronomy. In the years since the early s astronomers at Lick have used the Crossley for several historically important studies in stellar evolution, including the structure and spectra of planetary nebulae and the discovery and spectral analysis of faint variable stars in young clusters.
The Crossley has also contributed to studies confirming the expansion of the universe. In astronomer Edward A.
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Fath, using data collected with the Crossley reflector, established that none of the spirals observed had continuous spectra, but were in his opinion, clusters of individual stars. His conclusion was that spiral nebulae must be very distant and composed of very faint stars. Curtis devoted his efforts with the Crossley toward a better understanding of the nature of spiral nebulae.
In and Curtis published extensive lists and descriptions of the brighter nebulae and clusters that he photographed using the Crossley. Curtis' observations of numerous faint novae in the nebulae he photographed with the Crossley led to his conclusion that the nebulae were far more distant from the Earth than had previously been thought. Curtis concluded the nebulae were beyond our own galaxy. Curtis led the way in pushing forth the understanding of spiral nebulae as galaxies, giant island universes, external to our galaxy. In arriving at this view Curtis collided head on with astronomer Harlow Shapley, who held the opposite point of view in the famous Curtis Shapley debate held before the National Academy of Sciences, in Washington, DC.
In astronomer Robert J. Trumpler used data obtained from the Crossley to publish his classic paper in which he examined the distances, dimensions and space distributions of open star clusters. Trumpler proved conclusively that our galaxy does contain a layer of absorbing gas and dust which attenuates light of different colors by different amounts.
By properly taking into account this attenuation, Trumpler's work led to considerably smaller dimensions for our galaxy than had previously been considered. Continued contributions made by astronomers using the Crossley telescope in this century are almost endless.
Photographs of nebulae and clusters made with the Crossley reflector
Comets, asteroids, and satellites of the planets were regularly discovered. There were many studies of novae, planetary nebulae and their central stars, star clusters, and interstellar medium. Variable stars received attention, especially after photoelectric photometry became popular. In more recent years the Crossley has continued to be used as a scientific instrument, producing important new information in the study of astronomy.
The Crossley reflector was the first large reflecting telescope put into operation and used by astronomers at a first-class site. Using the Crossley, James Keeler and other astronomers at Lick determined the success of the reflector design for all subsequent large telescopes.