The Olcott Meridian Circle
The Olcott Meridian Circle was ordered by the Dudley Observatory’s first director, Benjamin Apthorp Gould, from the scientific equipment manufacturers Pistor and Martins of Berlin, Germany, in 1855. It was built in the next year and installed at the Observatory’s original site in North Albany in 1860. It was named for Thomas Olcott, an Albany banker who was a founder, trustee and major financial supporter of the Dudley Observatory.
A meridian circle telescope is used to measure very precisely the positions of stars. It is a refracting telescope that is fixed to point along a single north-south direction, while capable of rotation in the vertical direction from the horizon to the zenith (the point directly overhead). This varies the astronomical coordinate called declination. By positioning a star exactly halfway between the top and bottom of the telescope’s field of view, the declination can be read on large and precisely mounted engraved circles, attached to the telescope . Meanwhile the turning of the earth moves the chosen star across the telescope’s field of view. By precisely noting when that star crosses a fine wire stretched across the telescope’s aperture, an astronomer can very precisely measure the other astronomical coordinate, right ascension. The result was the 19th century’s most accurate method of measuring star positions.
The object-glass of the Olcott Meridian circle is a clear eight inches in diameter, and its focal length is ten feet. The two circles used to measure declination are each thirty six inches in diameter, initially inlaid with silver, and capable of being read, with the aid of microscopes, to within tenths of seconds of arc (one tenth of a second is one 36,000th of a degree). Using an electrical device controlled by a push button called a chronograph, the time when the star crosses the wire stretched across the telescope’s aperture, and therefore the star’s right ascension, can be determined with similar accuracy.
Only in the late 1870s was the Olcott Meridian Circle first used to carry out significant astronomical research. At that time, Lewis Boss, the Dudley Observatory’s fourth director, used it to measure the position of 8245 stars as part of an international sky survey effort coordinated by the Astronomische Gesellschaft in Germany. In 1893, it was moved to the observatory’s second site, on the south side of Albany, and was extensively refurbished, again thanks to the generosity of the Olcott family.
This led to the use of the Olcott Meridian Circle to carry out a more ambitious project, the determination of the positions of 33,342 stars arrayed around the entire celestial sphere. In order to achieve full sky coverage, the Olcott Meridian Circle was taken off its mountings in Albany in 1908, and shipped to San Luis, Argentina. There, over the next two years, 15,333 southern stars were observed, after which the telescope was returned to Albany. This supplemented the observation of 20,811 stars from Albany, an effort that concluded in 1918, No other high precision telescope on earth has ever made a survey of comparably extensive coverage (a modern more extensive higher accuracy survey was accomplished from space in the 1980s by the fully automated and computerized Hipparchos satellite). The results of these observations were combined with those of 238 other observatories world wide to produce the General Catalogue of 33,342 Stars.
After the sale of the Dudley Observatory’s second building in 1965, the Olcott Meridian Circle was disassembled and stored in the New York State Museum in Albany.
Pruyn Equatorial Telescope
The Pruyn Equatorial Telescope was purchased in 1893. It is a refracting telescope with a lens 12″ in diameter. It was built by the Warner and Swasey Company of Cleveland, Ohio, one of the world’s leading makers of scientific instruments. Its lens was made by John Brashear of Allegheny, Pa. Purchased with donations made by Charles and Robert C. Pruyn of Albany, it was named the Robert H. Pruyn Equatorial Telescope in honor of their father, a prominent 19th century Albany businessman, civic leader and long-time board member of the Observatory. It served science for more than 60 years, as well as being opened to public viewing every Tuesday night. In this capacity it introduced thousands of Albany residents to the wonders of the heavens. It was put in storage at the New York State Museum when the Dudley Observatory left its Albany site in 1965.
- More on the history and restoration of the Pruyn Telescope
- Brashear Catalog 1906 (PDF)
Pistor & Martins Transit Telescope
The Dudley Observatory’s Transit Telescope was purchased in 1863. It was made by Pistor and Martins of Berlin, Germany. It’s construction and operation are similar to those of the Olcott Meridian Circle. It was used for determining time based on the passage of stars across the meridian. Its object-glass was six and three-eights inches in diameter, with a focal length of eight feet. It saw little use, and was abandoned in the late nineteenth century.
Clark Comet Seeker Telescope
This telescope was made in the mid-19th century for the Dudley Observatory by Alvan Clark & Sons of Cambridge Mass. The Clark firm was one of the most prominent American telescope makers of the period and supplied fine instruments to many universities and observatories. “Comet Catcher” or “Comet Seeker” telescopes of this type were so called because of their relatively wide field of view and portability.
The comet catcher has a four inch object glass and a focal length of three feet. It was used by the astronomer Christian Henry Peters to make the first discovery ever by a Dudley Observatory astronomer, a comet found by Peters in 1857 and named for one of the Observatory trustees, Thomas W. Olcott. Later Dudley Observatory assistant Charles Wells used it in 1882 to discover the first comet of that year.
Fitz Equatorial Telescope
The Fitz Equatorial Telescope was purchased around1860 from the instrument maker Henry Fitz of New York City. Its objective lens is thirteen inches in diameter, with a focal length of just over fifteen feet. Although a relatively large telescope by mid-nineteenth century standards, defects in its construction and the limited budget of the Observatory led to its finding little use in astronomical research. When the Dudley Observatory moved to a new location in 1893, it was given away. In the 1990s, its lens was acquired by Arunah Hill Natural Science Center of Cummington, Mass. There it was remounted and put into use for public astronomical observation.
The Frank L. Fullam Radio Telescope
In 1970, the Carnegie Institution offered to Dudley Observatory the gift of a 100-foot parabolic radio telescope located in Maryland, near Washington DC. In January, 1971, the gift was accepted and the following summer the dish was disassembled under the direction of Dr. Joseph Erkes and trucked to a site near Bolton Landing, New York. Over the next four years the telescope was re-erected by Dudley on land leased from the State University of New York at Albany (University at Albany).
The project was funded by grants from many local contributors including substantial contributions by Ernest and Walter Fullam, in honor of their father – Frank L. Fullam. The dish was raised in November, 1973 and the official dedication of the Frank L. Fullam Radio Telescope took place on March 22, 1974. During the rest of the ’70s, the telescope was used by Dr. Erkes and Dr. Ivan Linscott in their work to develop a fast Fourier transform, a device to monitor astronomical phenomena that vary on a short time scale. By 1981, with the reduction of government research grants and the transfer of the device to Arecibo, questions were raised about the future disposition of the telescope. In the early 1990’s the buildings were destroyed, the antenna was dismantled, and the land returned to University at Albany.