The Allegheny Observatory is a large Neoclassical structure consisting of a first floor level and basement, on the wooded hills above the north bank of the Ohio River, in Riverview Park, Pittsburgh, Pennsylvania.  The building was designed by architect Thorsten E. Billquist, and built (1900-12) to be large enough to accommodate new discoveries and equipment in the field of astronomy. Biliquist worked closely with astronomer James E. Keeler and telescope maker John Alfred Brashear in its design.
The shape of the observatory building resembles a basilica, with a large rectangular block with two semi-circular rooms surmounted by two small domes flanking the entranceway, and a long hallway leading to a larger dome set at the opposite end. Designed to house three large telescopes, the three circular sections and domes dominate the facade and layout of the Allegheny Observatory.
The main entrance is covered by a pedimented portico supported by two Ionic columns. Double windows with plain flat frames and raised stone labels are located on either side of the doorway. The two smaller domes lie at the ends of this front facade. The left dome is surrounded by a stone porch supported by Ionic columns. Large plain windows line the walls of this section and smaller square windows are located directly under the dome. The right dome is plain and has only small rectangular slit-like windows.
The flat temple-like roof, pedimented entranceway and simple columns add to the classical appearance of the building. Decorative cut-out stonework forms a border along the roofline. The names of famous astronomers are cut into the lower cornice stone work just below the roofline.
With the completion of the building in 1912 the observatory was equipped with three primary telescopesa 13-inch Fitz-Clark refractor, the 30-inch Thaw refractor, and the 31-inch Keeler Memorial reflecting telescope. The 13-inch Fitz-Clark refractor, found in the small dome to the left of the front doorway, is today used primarily for public viewing during the observatory's evening tours. It is also used to test new auxiliary equipment for the other instruments. The 30-inch Thaw refractor housed in the main dome of the observatory is the largest photographic refractor in the country and was especially designed for photographic astrometry. The telescope tube is 47 feet long and weighs 8,000 pounds. The Thaw is used primarily to take 8 x 10-inch stellar photographs which are used in positional astronomy. In 1985 the original 30-inch glass lens in the Thaw telescope, made by John Brashear, was replaced with a new lens, designed to collect more light in the red end of the spectrum to cope with the increasing problem of light pollution in the Pittsburgh area. The original 30-inch lens is now on display in the main corridor of the observatory building. The 31-inch Keeler Memorial reflecting telescope, found in the small dome to the right of the front doorway, is used to photograph the spectra of the stars and to study double and multiple star systems.
Astronomer and physicist, James Edward Keeler (1857-1900), his son Henry Bowman Keeler (1893-1918), and telescope maker and former director of the Allegheny Observatory, John A. Brashear (1840-1920) and his wife Phoebe S. Brashear (1843-1910), are buried in vaults in the basement pier of the 31-inch Keeler Memorial reflecting telescope. A lifesize bronze statue of John Brashear, by Pittsburgh sculptor E. Victor, is on display in the main hallway on the first floor of the observatory.
The Allegheny Observatory at the University of Pittsburgh is significant because of its association with the careers of astronomers Samuel Pierpont Langley (1834-1906), James Edward Keeler (1857-1900), and telescope maker John Alfred Brashear (1840-1920). 
Langley was professor of astronomy and physics at the University from 1867 to 1887 and director of the Allegheny Observatory. During that time Langley invented the bolometer and used it in 1878 to make spectral observations of solar and lunar radiation. His paper on The Bolometer and Radiant Energy (1881) became a scientific classic. While Langley was the director, the Allegheny Observatory was the leading American observatory on matters relating to the study of solar physics.
James Edward Keeler succeeded Langley as director of the Allegheny Observatory and used the 13-inch Fitz-Clark refractor with a spectroscope to show, in 1895, that the rings of Saturn were rotating as a unit but that the inner boundary had a considerably shorter period than the outer. This was the first observational evidence that the rings were not solid but consisted of discrete particles circling the planet at different speeds.
John Alfred Brashear was named acting director of the Allegheny Observatory after Keeler's departure for the Lick Observatory in 1898. Brashear was a self-taught optician whose service to astronomy began in 1876 when he began to make astronomical telescopes. Over the years of his active career Brashear not only made both of the larger telescopes used at the Allegheny Observatory, but came to be recognized as one of the best telescope makers of his day. In the years since Brashear' a death in 1920 the Allegheny Observatory has used his telescope (the Thaw refractor) to do fundamental work in the field of astrometry, including the search for stars whose oscillations betray the presence of invisible companions.
The Allegheny Observatory was established in the wake of the appearance of Donati's Comet of 1858 when several prominent Pittsburgh businessmen formed the Allegheny Telescope Association. They purchased a 13-inch Fitz refractor, at that time the third largest telescope in the country, and built an observatory on the Northside hill in Pittsburgh, Pennsylvania. In 1867 the Allegeheny Observatory was transferred to the Western University of Pennsylvania, the forerunner of the University of Pittsburgh. The observatory became the home of the University of Pittsburgh Department of Astronomical Science.
Samuel Pierpont Langley was appointed as the first salaried director of the Allegheny Observatory. Langley was all but unknown when he arrived at the Allegheny Observatory in 1867, but when he left 20 years later he was world famous for his scientific achievements. During his term as director of the Allegheny Observatory he devised the "Allegheny System" of time keeping, which was based on measurements of star positions, and partially supported the observatory by selling accurate time signals to the railroads and the cities of Allegheny and Pittsburgh.
Langley devised his time-keeping service as a source of income for the Allegheny Observatory. While not the first time-keeping service in the country, it was the first to turn a considerable profit. During his administration, the time keeping service earned more that $60,000 and other observatories soon began to follow Allegheny's example.
Langley saw in his time service the means for establishing a national standard of uniform time. The Pennsylvania Railroad and its many subsidiaries were the most influential customers of the Allegheny Observatory's time-keeping service. In 1870 the Pennsylvania system extended some 2,500 miles and had some 300 telegraph offices receiving time signals. Eventually more than 8,000 miles of railway ran to the ticking of the time signals of the Allegheny Observatory. This uniform time service was not only profitable but necessary for the safe operation of the railroad. Timetables not only dictated train arrivals and departures, but, in the days before automatic signaling, also ensured that two trains did not meet head-on on the same stretch of single-line track. The system of uniform standard railway time became popular with the general public and led to the establishment of Standard Railway Time in 1883, and by 1918, the establishment of universal standard time.
Among Langley's other accomplishments was the study of sunspots with the 13-inch Fitz refractor, by then reworked by American astronomer Alvan Graham Clark (1832-1897), and the development of the bolometer to measure the amount of heat the sun radiated at different wavelengths. He used this instrument to make careful measurements of the quantity of solar radiation, both in the visible and invisible portions of the solar spectrum. In the process, he extended the knowledge of the solar spectrum into the far infrared for the first time. A unit of radiation equal to one calorie per square centimeter is called one Langley in his honor. In 1887 Langley left the Allegheny Observatory to become the Secretary of the Smithsonian Institution in Washington, DC.
Langley's successor was James Edward Keeler, an astronomer and physicist who would serve as the director of the Allegheny Observatory from 1891 to 1897. During his time at Allegheny, Keeler used the 13-inch Fitz-Clark refractor with a spectroscope to show that the rings of Saturn were not solid but are made up of particles circling the planet. This observation confirmed earlier theories proposed by Italian astronomer Giovanni Domenico Cassini (1625-1712) and Scottish physicist James Clerk Maxwell (1831-1879). With George Ellery Hale (1868-1938) Keeler founded the Astrophysical Journal, which became one of the leading professional astronomical journals. Keeler left the Allegheny Observatory in 1898 for the Lick Observatory in California. After Keeler's untimely death in California in 1900, his ashes were returned to the Allegheny Observatory for burial in a vault in the basement pier supporting the Keeler Memorial reflecting telescope.
John Brashear was named as the acting director of the observatory while Keeler's replacement was being sought. Brashear's service to astronomy began in 1876 when he first showed Langley a lens he had made. Impressed, Langley encouraged Brashear's lens making, and finally introduced him to William Thaw, a railroad businessman, who agreed to support Brashear in the making of telescope lenses. With Thaw' s financial support and Langley's encouragement, Brashear soon developed into one of the finest lens makers in the country. His lenses and mirrors are still found in many of the major refracting and reflecting telescopes in the world today.
After Brashear demonstrated his competence and all-around skill with optical instruments, he formed a business partnership with physicist Henry A. Rowland (1848-1901), of Johns Hopkins University, to manufacture gratings for spectroscopy. To give good spectra and get the most out of available light, a grating must be ruled with all of its grooves accurately parallel, and exactly evenly spaced. The larger a grating, the more efficient it is, but at the same time the more difficult it is to make. Rowland had developed in his laboratory at Johns Hopkins University a machine, Rowland's Ruling Engine, with which he could make gratings far superior to any previously known. Typically, his gratings would be several inches in diameter, ruled with 14,436 grooves per inch. These gratings revolutionized the study of spectroscopy, and astronomers everywhere clamored for them. These gratings, known as Rowland Diffraction Gratings, had a very accurate surface, no error of even 1/200,000th of an inch being allowed. Brashear supplied the accurately flat speculum-metal blanks, on which the gratings were ruled. Brashear's flat speculum-metal blanks when coupled with Rowland's Ruling Engine, produced diffraction gratings that supplied an invaluable tool to astronomers and physicists in the study of spectroscopy.
Another of Brashear's accomplishments was to arranged for David C. Park, a founder of Crucible Steel, to donate a plot of land in Riverview Park, in Pittsburgh, as the new location for the Allegheny Observatory. He also raised more than $300,000 to fund the construction of the new building. In addition, Brashear solicited Mrs. Willam Thaw, Jr., for additional funds to build a large 30-inch refractor dedicated to the memory of her husband and father-in-law. Brashear, personally, designed and built the 30-inch Thaw refractor.
On October 20, 1900, the corner stone of the new observatory was laid. Designed in the Classical style by the architect Thorsten E. Billquist, the new observatory was to be not only extremely functional but the beautiful focal point of the surrounding Riverview Park. When completed in 1912 the observatory was in possession of three major telescopes for its research program: the 13-inch Fitz-Clark refractor, the 30-inch Thaw refractor, and the 31-inch Keeler Memorial reflecting telescope.
In the years since the completion of the new building in 1912 the most important research work of the observatory staff has been in the area of astrometry. The telescope associated with this research is the 30-inch Thaw refractor. Large refractors are highly useful for this type of astronomical research because after their objectives have been installed they can be left undisturbed for decades. Any shift of one star with respect to its neighbors, barely measurable on photographic plates taken many years apart, is thus more surely a real displacement of the star and not some change in the condition of the optics.
The 30-inch Thaw refractor was designed by Brashear for this specialized area of research, photographic astrometry--the determination of the positions of celestial objects with great precision using photographs. The Thaw is the most successful telescope of this type in the world. For the last 75 years, it has been used to obtain data in three important areas. With it, astronomers have measured the distances to over 2,500 stars, or roughly 40 percent of all known stellar distances. It is also used to study the orbital motions of stars around each other and to determine the masses of stars. Finally, the Thaw is used in the search for planets revolving around stars; it is one of the few instruments in the world accurate enough to do such work.
In the years since 1912 the Allegheny Observatory has amassed a collection of more than 110,000 parallax plates resulting from observations with the Thaw telescope. This vast collection of data bearing the images of various star fields represents a continuity of information unmatched anywhere in the world.
By using this collection of photographic plates and new technologies such the Multichannel Astronometric Photometer (MAP), the Allegheny Observatory has remained in the forefront of research in the important field of astrotmetry. Indeed , through the use of repeated observation with the Thaw and the MAP, the Allegheny Observatory can compare this information with the wealth of data in its plate library, and offer the best chance astronomers have at present for observing extrasolar planets.
The Allegheny Observatory represents an important site associated not only with significant men in the history of the science of astronomy, Samuel Pierpont Langley, James Edward Keeler, and John Brashear, but also represents an important research institution where the instruments and data of the past are today coupled with the latest technologies, to continue the process of making new discoveries that are in the very forefront of astronomical research.
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(click on the above photographs for a more detailed view)