Fame

The Crossley 36-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. 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 extragalactic, but Keeler, using Crossley photographs, was the first to realize that these objects were a major constituent of the universe. After Keeler's death, astronomer Charles Dillon Perrine completed Keeler's observational program, and in 1908 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 1900s, 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. Large reflecting telescopes would now dominate 20th-century astronomy. The Crossley 36-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 36-inch reflecting telescope, at the Lick Observatory, marked the first modern application of a reflecting telescope to astronomical studies.

Sponsor

Edward Crossley was the eldest son of Joseph Crossley J.P., of Broomfield, Halifax, Yorkshire, of the Crossley carpets dynasty. He inherited his family's carpet manufacturing business (John Crossley & Sons) from his father when he was 27. He married Jane Eleanor Baines, third daughter of the Leeds newspaper proprietor and MP Sir Edward Baines. He was the Member of Parliament (MP) for Sowerby from 1885 to 1892. He was also mayor of Halifax from 1874–1876 and 1884–1885. He became a Fellow of the Royal Astronomical Society in 1867. He built an astronomical observatory and purchased a 36-inch (910 mm) telescope from Andrew Ainslie Common in 1885, and employed Joseph Gledhill as an observer. With Gledhill and James Maurice Wilson (later Canon of Worcester), he wrote Handbook of Double Stars in 1879, which became a standard reference work.

Construction

The Crossley 36-inch reflector at the Lick Observatory was built by British amateur astronomer Andrew Ainslie Common in England in 1879. Common planned the telescope, mounting, and housing himself while the 36-inch silver-on-glass reflector mirror was designed and built by the English telescope maker George Calver. In 1884 Common sold his 36-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 1893. 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. Since the observer's working area on the platform for the telescope was too exposed to the weather, Crossley designed and constructed a substantial dome to house the telescope. The new dome was 39 feet in diameter and covered with 1/12-inch galvanized iron. The dome weighed 15 tons and was driven by a water engine that turned it through a complete revolution in five minutes. Pipes under the floor carried hot or cold water to heat and cool the dome when not in use. The observer's platform was suspended inside the dome and rotated with it. By 1893 Crossley became dissatisfied with the climate of England for astronomical work and decided to dispose of the 36-inch reflector and dome. After an exchange of letters with Edward S. Holden, the director of the Lick Observatory, Crossley agreed to donate his telescope to Lick. During the summer of 1895 the large 36-inch reflector was taken down and shipped to California. The massive dome built to house the telescope was also sent to Lick. By June 1896 the telescope was installed on Mount Hamilton and ready for operation.

Specification

The telescope was equipped with the f/5.8 newly refigured mirror B, which proved to be of excellent quality. However, due to problems in the original mounting, it proved difficult to take satisfactory long exposures. On January 1, 1898, James E. Keeler assumed the directorship of the Lick Observatory and began to work with the Crossley reflector. Keeler immediately began to make modifications to the telescope to improve its optical qualities and working characteristics. Keeler cut down the pier that mounted the telescope by two feet, thus lowering the telescope by a similar amount to provide more clearance between it and the dome. At the same time the top of the pier was finished off with a slight bevel, so that the polar axis was parallel to the axis of the rotation of the Earth. These changes in the mounting of the telescope were necessary to compensate for the difference in latitude between Common's observatory in England and Mount Hamilton. Other modifications included the addition of a windscreen, a new and smoother drive clock and improvements to the drive train and double-sided plate holder. Keeler also adjusted the mirror of the telescope so that its optical axis was accurately aligned with the centre of the tube, and added a new low-power finder telescope, for picking the right area of the sky, to work with the existing high-power telescope. The latter was given a new and lighter-weight mounting. Although Keeler was able to work successfully with the telescope and produce exposures up to four hours by 1899 the instrument still proved difficult to handle and inadequate for longer observations. The major problem was the insufficiently rigid mounting, which failed to hold the telescope steady in high winds and flexed excessively at large zenith distances. Adding to these problems was the occasional slippage of the mirror in its cell. James Keeler produced a large number of scientific papers based on his work with the Crossley before he died on August 12, 1900. The next astronomer to work with the Crossley was Charles Dillon Perrine. 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 1902 to 1905, 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. With these modifications, the Crossley became a faster and more efficient telescope for photographing nebulae and star fields. The Crossley remained unchanged until 1934 when the large 36-inch mirror was coated with aluminum, thus increasing its light-gathering capacity. In the early 1950s, 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 1960s 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.