Allegheny Observatory

About this property

The Allegheny Observatory is an American astronomical research institution, a part of the Department of Physics and Astronomy at the University of Pittsburgh. The facility is listed on the National Register of Historic Places (ref. # 79002157, added June 22, 1979) and is designated as a Pennsylvania state and Pittsburgh History and Landmarks Foundation historic landmark. 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 known as the 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, dormitories, and a lecture hall. === Langley’s 1869 establishment of the Allegheny Time System === In 1869, Langley created income for the observatory by selling subscription service to time that was accurately determined by astronomical measurements and transmitted over telegraphs to customers. The Pennsylvania Railroad was the most influential subscriber to the "Allegheny Time" system. The Allegheny Observatory's service is believed to have been the first regular and systematic system of time distribution to railroads and cities as well as the origin of the modern standard time system. By 1870, the Allegheny Time service extended over 2,500 miles with 300 telegraph offices receiving time signals. 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. In 1878, Langley invented the bolometer, which makes very sensitive detections of thermal radiation. He used it to measure the strong variation with wavelength of Earth’s atmospheric absorption, results used by Arrhenius in 1890 demonstrating the greenhouse effect. Langley also used it to discover new infrared atomic and molecular absorption lines and make the first accurate calculation of the solar constant. Bolometers are now essential physics instruments with applications extended to astronomy, particle physics, plasma physics, and thermal cameras.

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Property data from the National Register of Historic Places, National Park Service (public domain).

Description adapted from Wikipedia under the Creative Commons Attribution-ShareAlike 4.0 International License.

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