Fame

The Bruce Astrograph was undoubtedly one of the most famous of all Astrophotography Cameras. It was used by the great Edward Emerson Barnard to take some of the finest, and also some of the most important astronomical photographs ever produced. In 1895 Barnard left the Lick Observatory when he was appointed Professor of Astronomy at the University of Chicago. It was here at the Yerkes Observatory (part of the University of Chicago) that he began taking the long exposure photographs of the Milky Way which were later published as an 'Atlas of Selected Regions of the Milky Way'. The photographs in this atlas were obtained by the Bruce Astrograph. Initially the Bruce Astrograph had been located at the Yerkes Observatory in its own Dome. However 40 of the 50 photographs of the Atlas were obtained during a nine month stay at Mount Wilson in 1905. At the invitation of George Ellery Hale, director of the newly founded Mount Wilson Solar Observatory of the Carnegie Institution of Washington, Barnard had transported the Bruce telescope to the clear mountain side with its steady atmosphere. Funds to publish the Atlas had been guaranteed by the Carnegie Institution in 1907. However, Barnard, ever the perfectionist, worked for many years on the assembly and the descriptions of the photographs, and on the inspection of the 35,000 photographic prints that were required for the 700 copies of the Atlas that eventually would be printed. However, he did not complete the task by the time of his death in 1923. The work was finished by Edwin B. Frost, then director of the Yerkes Observatory, and by Barnard's niece Mary R. Calvert. This two volume Atlas, one volume of the photographs and the other a description of each field, was finally published by the Carnegie Institution in 1927 as a Carnegie Publication number 247. The photographs in this Atlas remain a valuable data source for studies of the Milky Way, its star clouds, the numerous open clusters, and especially for the dark regions of the Barnard dark clouds, first made manifest in these photographs. The dark clouds proved to be singularly important in the discovery of dark matter between the stars, rather than voids in the heavens. Barnard was the first astronomer to provide this decisive evidence for their existence from these photographs. The Bruce Astrograph now lies in bits in a basement of the Yerkes Observatory, all but forgotten.

History

The funding for the Astrograph came from Miss Catherine W Bruce who donated in 1897 to the Yerkes Observatory, the sum of $7000 for its construction and an observatory to house it. The telescope was a compound of three separate telescopes, a 10 inch "doublet" of 50 inches focal length; a 6.25 inch lens of 35 inches focal length, and a 5 inch guiding refractor, all mounted into a single structure to form a powerful photographic survey instrument. John Brashear ordered the Glass Blanks for the 10” Achromatic Objective from Mantois of Paris. These were delivered in May 1899, and by the September 1900 Brashear had completed the Doublet. The objective produced a perfectly flat field of some 7 degrees, and an overall acceptable field of 9 degrees. The Focal Ratio of the main 10” telescope was ‘f5’. The instrument was finally completed and placed in its observatory in April 1904.

Technology

The mounting of the Bruce Astrograph was considered by Barnard to be particularly important. His experiences with the earlier Crocker Astrograph had taught him that the ordinary German Equatorial it used was not entirely suitable for long exposure photography, particularly when near to the meridian. In order to solve this problem he consulted with the firm of Warner & Swasey of Cleveland. The solution adopted was ingenious; the pier of the telescope itself was bent to form the Polar Axis of the mount. In this way the telescope could move freely in all directions either side of the meridian. The optics of the Bruce astrograph was left to Dr. John Brashear of Allegheny (now part of Pittsburgh), Pennsylvania, and a leading astronomical instrument of that time, who had worked previously on the Crocker Astrograph’s mount and optics.