The Allegheny Observatory is an American astronomical research institution, a part of the Department of Physics and Astronomy at the University of Pittsburgh.

In 1869, Langley created income for observatory by selling subscription service to time that was accurately determined by astronomical measurements and transmitted over telegraphs to customers.

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.

Keeler's observations launched the detailed study of Saturn's rings, which today yield insights into less accessible disk systems.

John Brashear (Allegheny Observatory Committee Chairman: 1893-1920, Allegheny Observatory Director: 1898-1900, University of Pittsburgh Chancellor: 1901-1904) made many high-quality optics and precision instruments at his Allegheny-Observatory-affiliated shop, including the optical surfaces for the famous 1887 Michelson-Morley interferometer, which demonstrated the constant speed of light regardless of motion direction.

This was the most successful photographic parallax telescope in the world, establishing the most-accurate distance scale for the local Universe in the early 20th century.

Observatory staff advised him that the lens of the 13 inch Fitz Telescope had been taken for ransom which Langley refused to pay; an argument with the unknown lens-napper ensued without resolve.

The lens-napper thought that with the involvement of the newspapers investigating the incidents his identity may be discovered so told Langley he could have back the lens.

To study the aerodynamic behavior of different forms traveling at speeds up to 70 mph, he built a 30' spring "whirling arm" to which stuffed birds and wings he made were attached.

The building is a tan brick and white terra cotta hilltop temple whose Classical forms and decoration symbolize the unity of art and science.

The L-shaped building consists of a library, lecture hall, classrooms, laboratories, offices, and three hemispherical domed telescope enclosures.

The core of the building is a small rotunda, housing an opalescent glass window depicting the Greek muse of astronomy, Urania,[12] designed by artist Mary Elizabeth Tillinghast.

In 2009, the university's Department of Geology and Planetary Science installed Western Pennsylvania's only seismic station, which is connected to IRIS Consortium networks, in the observatory.

When the new facility first went into operation, on every clear evening it was opened for the public to look through the 13" telescope but if it were a cloudy night "they would be given an illustrated lecture on astronomy."