History
The observatory was founded on February 15, 1859, in the city of Allegheny, Pennsylvania (incorporated into the city of Pittsburgh in 1907) by a group of wealthy industrialists calling themselves the Allegheny Telescope Association. The observatory's initial purpose was for general public education as opposed to research, but by 1867 the revenues derived from this had receded. The facility was then donated to the Western University of Pennsylvania, today's University of Pittsburgh.
The University hired Samuel Pierpont Langley to be the first director. One of the research programs initiated under his leadership was of sunspots. He drew very detailed drawings of sunspots which are still used in astronomical textbooks to this day. He also had the building expanded to include dark rooms, class rooms, dormatories, and a lecture hall.
On November 18, 1883, the first day of railroad standard time in North America, the Allegheny Observatory transmitted a signal on telegraph lines operated by railroads in Canada and the United States. The signal marked noon, Eastern Standard Time, and railroads across the continent synchronized their schedules based on this signal. The standard time that began on this day continues in North American use to this day.
The revenues from the sale of time signals covered Langley's salary and the bills. Allegheny Observatory continued to supply time signals until the US Naval Observatory started offering it for free in 1920.
More recently George Gatewood began using the Allegheny Observatory to search for extrasolar planets as well as to follow-up on claims of extrasolar planets, starting in 1972. This is done using astrometry, which is the practice of measuring the position of stars. In addition to studying the positions of stars on the thousands of photographic plates in the vaults of the observatory, George Gatewood also designed the Multichannel Astrometric Photometer (MAP) for use with the Thaw telescope to measure the position of a target star and its close neighbors on images taken 6 months apart. This technique takes advantage of parallax. If the target star has a companion then it will wobble due to the gravitational pull of the unseen companion. The size of the companion can be measured by the size of the wobble.
MAP is no longer in use and the Thaw telescope is in the process of rewiring and upgrading.
A model of the original observatory can be found in the Miniature Railroad & Village exhibit at Carnegie Science Center in Pittsburgh and in 2012 a documentary film was released covering the observatory's history.
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