nothing now remains of this addition to the Gaithersburg Latitude Observatory. History The Gaithersburg observatory was established as part of the International Polar Motion Service in 1899. The Gaithersburg observatory was built by Edwin Smith, chief of the Instrument Division of the U.S. Coast and Geodetic Survey, who had conducted similar measurements as a volunteer in 1891-92 from his home in Rockville, Maryland. During its operation twelve groups of stars were studied in the program, each group containing six pairs of stars. Each night, the station observed two of the star groups along a preset schedule and later compared the data against the measurements taken by the five sister stations. The station operated on this schedule until 1915, when it was temporarily closed as a result of economy measures. Operations resumed in 1932 and continued until 1982 when advances in computer technology and satellite observations rendered it obsolete, although data collected by the observatory over the years still has use to scientists, and has been applied to studies of polar motion, the physical properties of the Earth, climatology and satellite tracking and navigation. Description The Gaithersburg Latitude Observatory stands on the north side of DeSellum Avenue, just north of the Gaithersburg High School campus. The building measures square with a small gable-roofed louvered entrance porch on the west side. There is a small shed-roofed addition on the east side. The structure rests on a mortar and fieldstone foundation. Each gable features a decorative wood five-pointed star. A metal ventilator is mounted over each half-section's roof, topped with similar metal star. A system of metal-capped wood rails allows the building to be pulled apart in the middle using ropes and pulleys. The halves operate independently. The structure is double-walled, with an inner frame of 4×4s sheathed with tongue-and-groove boards, separated by from the outer, louvered wall, also framed with 4×4s. On the interior, a double floor surrounds a pyramidal concrete pier that supported the observing instruments. A 1½ story brick caretaker's house, built in 1947, is located to the south; it is excluded from the landmark designation. The site was extensively surveyed and documented to support its mission. The Meridian Mark Pier, about to the south, was used to align the zenith telescope. Five Coast and Geodetic Survey monuments are on the property. The RM-1 monument has been used by NOAA for testing associated with the Global Positioning Satellite system. See