History of Allegheny Observatory
The Allegheny Observatory was born February 15, 1859 when three citizens of Allegheny City met at the office of Professor Lewis Bradley to consider the purchase of a telescope, "the magnifying power of which would bring the heavenly bodies near enough to be viewed with greater interest and satisfaction". These men and 29 others later formed the Allegheny Telescope Association.
This club eventually purchased a 13" refracting telescope from Mr. Henry Fitz of New York. It was delivered to the new observatory building on Pittsburgh's northside on November 14, 1861. First light for the Fitz Refractor was November 27, 1861. During this period the telescope was used almost exclusively for the entertainment of the members. The moon and planets were the most popular subjects and there is no evidence that any research was done with the telescope.
By May 1867 interest in the observatory had waned and the declining membership, being in debt, voted to donate the telescope and observatory building to the Western University of Pennsylvania, later to become the University of Pittsburgh. In that same year the observatory was infused with new life through the appointment of Professor S.P. Langley as Director of the Observatory and Professor of Astro-Physics. The observatory received new scientific direction. Langley used the telescope to study the sun, especially sunspots and heat from different parts of the solar spectrum. At last true research had come to the Allegheny Observatory .
Through the friendship and aid of William Thaw, a Pittsburgh industrial leader, Langley was able to improve the observatory equipment and build additional apparati. One of the new instruments was a small transit telescope used to observe the position of the stars as they cross the celestial meridian. With this instrument Langley obtained accurate time. Realizing the need many industries, especially the railroads, had for accurate, uniform time, Langley arranged to send time to subscribers through the telegraph.
The money paid by these users, nearly $3000 annually, helped finance the observatory's research, pay staff salaries, and help maintain the building. One of Langley's greatest interests was to see the observatory put on sound financial footing.
On June 1 1891, Professor Langley's assistant, James Keeler, succeeded him as Director of the Allegheny Observatory and Professor of Astro-physics. Keeler's investigations here fully maintained the splendid reputation established for Allegheny by his predecessor. Keeler's observations of the spectrum of Saturn's rings are of extraordinary interest. Considering the means at hand, they have never been surpassed in excellence or beauty. Keeler's spectrographic proof showed that every point in the ring system is moving with the velocity which a moon would have if situated at that distance from the planet. With the 13" Fitz refractor Keeler had provided the visual proof that the rings of Saturn were particulate.
Keeler recognized the shortcomings of the original Allegheny Observatory and began to draw plans for a new one with a 30" refractor as the primary research instrument. However, prospects for success in this regard discouraged him and he ultimately accepted directorship of the Lick Observatory on March 8, 1898.
Upon the resignation of Keeler, John Brashear, the internationally know lens maker and Chairman of the Observatory Committee, became the interim director. During this time the plot of land for the new observatory was secured and the job of raising the capital for the building was begun.
In a letter to Frank Wadsworth, Keeler said, "When I do leave Allegheny, it will give me much pleasure to recommend you as my successor." In 1899 Professor Wadsworth took up the directorship and immediately set about supervising the building plans for the new observatory. His final drawings closely parallel those of T.E. Billquist, the architect who designed the present structure.
The 30" Thaw telescope is the primary instrument of the Allegheny Observatory. It is the third largest refractor in the United States and was constructed by the Brashear Co. It has a lens made from two glass disks cast by the Shott Co. of Germany. It was originally designed to be a visual refractor but Professor Schlesinger, Wadsworth's successor, thought a photographic instrument was needed. The original lens was designed by Professor Charles Hastings to be used with photographic plates which were sensitive to blue and ultraviolet light. The Thaw telescopes' primary mission has been to study the distance to nearby stars. The parallax program begun by Professor Schlesinger is responsible for the collection of over 110,000 photographic plates in the Allegheny collection. Information gathered from the Thaw observations have helped set the distance scale of the universe.
The second largest dome of the Allegheny Observatory houses the James E. Keeler Memorial Telescope. The Keeler Memorial is a reflecting telescope with a mirror 31 inches in diameter. Friends of James Keeler donated the funds for the instrument which was built by the Brashear Co. The Keeler reflector was originally used to determine the orbits of spectroscopic binaries, stars that are so close that they appear even through a telescope as 'one'. With the Mellon spectrograph attached the stars could be recognized as a pair through the study of their spectra. The Keeler has also worked on the solar spectrum and more recently quasar studies.
In addition to the basic parallax program, there have been other areas of study at Allegheny. Director Frank Jordan kept up a photometric program on variable stars. He established definitive light curves for 29 Cephied variables and 16 eclipsing binaries. Nicholas Wagman, director after Jordan, was responsible for the largest program of stellar parallax and proper motion of his time, the determination of over 400 target stars parallaxes and the discovery of many unseen companions. Under the previous director, Dr. George Gatewood, Allegheny was involved in a program to detect extrasolar planets. Under Dr. Gatewood, the Thaw telescope has been modernized, including a new lens that works best in red light. Replacing the glass plate as the stars image detector is the Multi-channel Astrometric Photometer(MAP). Light from up to 12 stars is fed into separate detectors by fiber optics as a Ronchi ruling with four lines per millimeter is passed across the field. Computer analysis of the times of the resultant intensity variations permits extremely precise positions to be derived from only a few minutes of observation. It is this technology that provided proof that Lalande 21185 had planetary companions.
Now over 130 years after its birth, the Allegheny Observatory continues its quest to unravel the mysteries of the universe. As an unparalleled leader in the field of astrometry, Allegheny will continue it search for extra solar planets.
--Arthur E. Glaser--
University of Pittsburgh
Department of Physics & Astronomy
159 Riverview Avenue
Pittsburgh, PA 15214
Last Modified 03/04/2021