The Gaithersburg Latitude Observatory is a small, 13-foot-square one-story building. There is a wooden louver-covered gable roofed entrance porch on the west facade. The original porch door is missing. There is a small shed-roofed ell on the east side. The building has a concrete mortar and fieldstone foundation. The gable roof consists of two sections that move apart on wheels exposing the center interior of the building. The roof is constructed of inch tongue-and-groove board. In the eaves, the rafter ends are cut back and covered by a tilted fascia board. A decorative wooden five-pointed star is mounted in the center of each gable end.
The inner wall plates consist of double two by eights resting on edge. On the north and south walls, these plates extend about three feet beyond the building to support the roof in its open position. These extended plates are capped with four by fours supporting the metal U-track in which the roof wheels travel. Parallel to the U-track, about six inches into the building and down about four inches, are a pair of one-inch-thick iron rods. These rods extend the length of the north and south plates, piercing the east and west walls. They are moved from inside the building. Each section can be moved independently by a rope and pulley system. There are two decorated ventilators, one on each roof section near the center of the building. As a part of the decoration, a metal five-pointed star caps each ventilator.
The building is double walled. The inner wall consists of four by fours over layed with tongue and groove boards on the inside. There is a nine-inch space between the walls. The outer wall consists of four by fours covered on the outside with horizontal framed wooden louvers. The outside walls are connected to the inner walls only at the building corners, the entrance and the door to the east ell. The inner and outer sills appear to rest on the foundation. The exterior wall ends at the ground in a bevelled wooden water table. There is a double floor in the main room with a concrete pyramid-shaped pier in the center of the dirt floor that is sunk four feet below the floor and tapers as it extends up to about waist height. The observing telescope and instruments were mounted on it. The telescope is now in storage in Corbin, Virginia. The southern wall has a central section of two by three feet which can be lowered to expose two sliding wooden sashes in the inner wall.
About 200 feet to the south of the observatory is the Meridian Mark Pier (azimuth marker), a green metal pagoda-shaped object about four feet high by two feet square, which was used to align the Zenith Telescope.
Five Coast and Geodetic Survey monuments are located on the property of the observatory. These monuments establish exact geographic longitude and latitude positions, elevation above sea level, and the direction of the magnetic north field of force. The Observatory RM-1 monument, dated 1966 is still used by the National Oceanographic and Atmospheric Administration (NOAA), for positional testing of new technology in the Global Positioning System (GPS) Receiver which tracks orbital satellites. A 1-1/2 story brick caretaker's house and garage. constructed in 1947, is seventy-feet to the south of the observatory building.
The United States Coast and Geodetic Survey Superintendent's Report for 1898-99 records an agreement reached by members of the International Geodetic Association to establish six observatories for the purpose of measuring the variations in latitude caused by the earth's wobble on its polar axis. This program, known as the International Polar Motion Service, was initiated in 1899 with the establishment of six stations, all located near the parallel of 39 degrees 08 minutes north latitude (to permit uniform computations), and were at Gaithersburg, Maryland; Cincinnati, Ohio; Ukiah, California; Mizusawa, Japan; Charjui in Russian Turkestan; and Carloforte, Sardinia, Italy. Economic constraints forced the closing of the Cincinnati observatory in 1932. The Charjui station was lost in World War I, and an observatory was substituted for it at Kitab, near Samarkand in the Soviet Union.
The Gaithersburg Observatory was constructed by Edwin Smith, Chief of the Instrument Division of the U.S. Coast and Geodetic Survey (This agency, now the National Oceanic and Atmospheric Administration, operated the International Polar Motion Service observatories in the United States.) Between 1891 and 1892 Smith had been conducting measurements of the variation of latitude on a volunteer basis from his home in Rockville, Maryland, and made nearly 1800 individual measurements on 146 nights, until his regular work forced him to discontinue his observations. However, when the International Geodetic Association allocated funds for the purchase of land in Gaithersburg in 1898, Smith was entrusted with the construction of the Gaithersburg Observatory, which began operating on October 18, 1899.
The original six observatories around the world worked in close concert carrying out a program of star study selected by Dr. Kimura, the astronomer in charge of the Mizusawa station. Twelve groups of stars, each containing six pairs of stars, were selected. Two groups of stars were observed each night at each station in accordance with a schedule of dates, time, and duration prepared by Dr. Kimura. The irregular daily motion of the earth's axis was believed to be extremely small, but the extent could be determined by the precise measurements of the stars. The six stations worked documenting the data to support latitude variations until 1914. Economic constraints forced the closing of the Gaithersburg and Cincinnati stations in 1915. During World War I contact was lost with the Charjui station. When communication with the Russian observers was resumed, the association learned that star movement data had been recorded through 1919. After World War I the Soviets continued to participate in this program with the establishment of a new station in Kitab in Uzbekistan, USSR.
While the Cincinnati station remained closed and was eventually dismantled, the Gaithersburg Latitude Observatory resumed operations in 1932. Upon reopening, it functioned continually in cooperation with its sister observatories through out the world until computerization rendered its use obsolete in 1982.
The scientific work conducted at the Gaithersburg Latitude Observatory illustrates the systematic approach sought by the International Geodetic Association to measure the degree of "wobble" occurring on the earth' s north-south axis. Although superseded by newer technologies using satellite observations the wealth of data returned from Gaithersburg and the other five observatories is used by scientists today to determine polar motion; the size, shape and physical properties of the earth; to predict climate and earthquakes; and to aid the space program through the precise navigational patterns of orbiting satellites.
The city of Gaithersburg designated the observatory as a local historic site in December 1983. In July 1985 the site was listed in the National Register of Historic Places. The observatory property was conveyed to the city of Gaithersburg in May 1987 by the federal government, with the proviso that it be preserved as a historic monument and used for the benefit of the public. At the present time the city of Gaithersburg plans to restore the latitude observatory and build a science education center, on the site of the caretaker's house, for the use of the school children of Gaithersburg.