Celestial Reference Frame Department History

The Astrometry Department has existed in various forms since the 19th century. For much of its history its main concern has been the operation of transit circles. In the late 1950's two departments, the six-inch transit circle and the seven-inch transit circle divisions, were responsible for the operation of the two instruments and the data analysis and production of the observational catalogs. The Equatorial Division operated the 26- inch refractor, mostly for double star research. In 1969 the seven- inch transit circle was sent to El Leoncito, Argentina to observe the southern component of the International Reference Stars, the SRS.

The six-inch transit circle observed the northern component of the IRS, the AGK3. At the time the names of the divisions were changed to Northern and Southern Transit Circle Divisions. In 1977 the seven-inch transit circle was returned to Washington where an image dissector micrometer system was developed and installed. The two Divisions were combined with the Equatorial Division to produce the Astrometry Department.

The seven-inch transit circle was sent to Black Birch, New Zealand, to observe the second epoch of the SRS, while the six-inch transit circle observed the IRS in the North. An 8-inch twin (yellow and blue lens) astrograph was acquired and sent to Black Birch to photograph the southern sky. These projects ended in 1995 and the seven-inch transit circle was removed from Black Birch and placed in storage in Washington. The six-inch transit circle remains operational (and celebrated 100 years of operation in 1997 with a brief set of measurements made by T. Rafferty), but the successful operation of the European Hipparcos satellite effectively obsoleted the transit circles.

In 1997 the astrograph mentioned above was fitted with a new "red" lens and a 4kx4k CCD camera and sent to Cerro Tololo, Chile to begin a program of observing the southern sky to unprecedented accuracy from the ground.

6-inch Transit Circle

* see Transit Circle Division below.

9-inch Transit Circle

** the 9-inch Transit Circle Division was decommissioned at Morgan's retirement in 1944

7-inch Transit Circle