In the scientific community, the Smithsonian Astrophysical Observatory (SAO; also referred to as APO) has held a prestigious position since its inception. The Astrophysical Observatory itself was a direct result of the efforts made by Secretary Samuel Pierpont Langley, who was also its first Director.
Samuel Pierpont Langley was a self-taught man without benefit of a higher education. Langley was an intelligent man who knew he wanted to be involved in all aspects of the scientific process. By 1880, he had perfected the instrument known as the bolometer. The device could be used to measure heat and was best suited for quantitative scientific work because of its stability and the ability to repeat data. Langley has been called a scientist, an engineer, a naturalist, and an historian. In truth, he had to have been all of the above to establish himself as a world figure in astrophysics. With what he termed, "The New Astronomy," Langley created a science that focused on the sun and its effects. In 1887, while working at the Allegheny Observatory in Pennsylvania, Langley was asked to join the staff of the Smithsonian as Assistant Secretary under Spencer Baird and to help with the creation of the SAO. Quite unexpectedly, and after only a short period of time in Washington, Langley became Secretary of the Institution, and under his direction, ground was broken on the Smithsonian Astrophysical Observatory in November 1889.
The Observatory building was originally located on the southeast side of the Castle Building, on Smithsonian Institution grounds. During construction several obstacles were overcome to create a suitable building. The first major problem came as a result of the vibrations from the busy Washington streets. The heavily trodden ground made it impossible to make sure that the collected data were accurate. This problem was eradicated by raising the structure off the ground and supporting it on deeply-set pylons. The second obstacle facing the Observatory was the oppressive summer heat and humidity of Washington. What resulted was one of the first year-round constant temperature spectroscopy rooms, controlled by an ammonia refrigeration system, with a continuous temperature of twenty degrees centigrade. Thus, the Smithsonian was the first institution with an air-conditioned astrophysical observatory.
It was during these early years of the SAO that Charles Greeley Abbot, a twenty-three-year-old from Boston, was hired on as an Observatory assistant. He worked with Langley, learning the principles of bolometry and spectral radiometry. In 1906, Abbot was asked to take over the Observatory from Langley, who wished to pursue his attempt at manned, heavier-than-air flight with his "aerodromes." With Abbot came the move away from long-term programmatic studies and onto short-term research projects. These were not as narrowly focused and thus covered a broader range of topics and influences from physical theory in observation and experimentation.
Under Director Abbot, the Observatory established field stations to achieve a diversified collection of solar constant values. The stations were strategically placed to ensure diversity in the readings, with the first station opened at Mount Harqua Hala, near Phoenix, Arizona, in use from 1920-1926. Also established in 1920 was Mount Montezuma, in Antofagasta, Chile, which maintained observations through 1955. The Montezuma station closed only when the skies became too cloudy and the air too filled with smog, from the local mines, to continue observations. In 1925, the Observatory opened the Table Mountain station in Swartout, California, which would remain in use longer than any of the other stations, closing in 1962. In Africa, the Observatory established two stations, the first at Mount Brukarros, located in Southwest Africa, in use through 1932, and the others near Mount Sinai, Egypt, on Mount St. Katherine, 1933-1937. In Silver City, New Mexico, the Tyrone station was in use from 1938-1946, also closing because of increasingly poor air quality and sky conditions. The SAO made attempts to relocate the stations that they were forced to close or abandon. One such attempt was made at Clark Mountain, in California, but sufficient funds were unavailable for this field station in 1948.
At Abbot's retirement in 1944, he was succeeded by Loyal B. Aldrich, who had worked for the Observatory for thirty-five years. Aldrich continued as Director until retiring in 1955. At that point Secretary Carmichael had approved the Observatory's move from Washington and began looking for a suitable location. With the growing concerns facing the Observatory, Carmichael felt that a move would be the best solution. In 1953, new worries concerning the future of the SAO escalated with the impending retirement of Aldrich and the unexpected death of his intended successor, William H. Hoover. It was at this time that Secretary Carmichael looked into moving the SAO to Climax, Colorado, and began discussions with Fred Whipple. After careful consideration, Carmichael decided that the lack of an astrophysical research program at the local university would diminish the availability of appropriate facilities for the SAO's use. Secretary Carmichael decided instead on a move to the Harvard College Observatory (HCO),Cambridge, Massachusetts. This move allowed a symbiotic relationship between the two observatories, but also ensured their recognition as two separate facilities.
By moving the SAO to the Harvard College Observatory, the Smithsonian would gain access to the network of solar research stations operated by Harvard, including the Sacramento Peak Observatory. Direct connections between the SAO and the HCO (via Sacramento) would facilitate further research in astrophysics, and new government contracts could be expected. The move from Washington, D.C. to Cambridge officially took place on July 1, 1955, under the Directorship of Fred L. Whipple.
While at the HCO, additions were made to the work with which the SAO was involved. They were an integral force in tracking the paths of satellites in "Operation Moonwatch;" the SAO began the series of "Smithsonian Contributions to Astrophysics," as well as establishing a Photographic Meteorite Program and the Center for Short-Lived Phenomena. In 1968, they opened yet another field observatory at Mount Hopkins, Arizona, to house the first multiple-mirrored telescope.
On July 1, 1973, the Smithsonian Astrophysical Observatory merged with the Harvard College Observatory to become the Harvard-Smithsonian Center for Astrophysics, or CFA, located at Cambridge, Massachusetts.