The U.S. Naval Observatory dates from 1830 when the Depot of Charts and Instruments was established under the control of the Navy Department to care for chronometers, charts and other navigational equipment. By a Congressional appropriation of 1842 the Depot was re-established in 1844 in new permanent quarters on the knoll north of the present Lincoln Memorial, at 23rd and E Streets NW, in Washington, DC. In 1854 the institution was officially designated the United States Naval Observatory and Hydrographic Office. The Hydrographic office was officially separated in 1866. 
The E street site proved to be a poor choice for an astronomical observatory due to the mud flats and swampy land immediately to the south and west and the closeness of the Potomac River which caused foggy conditions. Since the Naval Observatory required a clear atmosphere free from the smoke and heat radiation of nearby buildings, in 1880 the Congress authorized the purchase of a new site. The area chosen was the 73-acre Barber estate in the country north of Georgetown, presently 34th St. and Massachusetts Ave., NW, in Washington, DC. At the time of the purchase the site contained a mansion, stable and many outbuildings. This new site was chosen for the rural character of the estate and the fact that the land had the highest elevation in the Washington, DC, area. The architect for the Naval Observatory was Richard Morris Hunt, who began work on the original nine buildings in the Spring of 1887. By 1893 the new Naval Observatory was in operation.
To protect the integrity of the astronomical instruments from unwanted vibrations that would interfere with operations, Congress passed a Joint Resolution August 1, 1894 (28 Stat. L. 588), prohibiting the construction of any highways within the area of a circle described with a radius of one thousand feet from the center of the clock room of the observatory. The circle thus described marks the official boundary of the observatory. In 1988 the District of Columbia Zoning Commission provided further protection for the Naval Observatory by declaring the area immediately adjacent to the observatory as a Naval Observatory Precinct District.
The following buildings, designed and constructed under Hunt's supervision, contribute to the significance of the Naval Observatory as a National Historic Landmark.
The Main Building, now known as the James Melville Gilliss Building, is 69 feet wide and 307 feet long. This building has two stories and a basement with stone and brick walls , and houses the offices of the Naval Observatory and the Oceanographer of the Navy. The east end of the building has a circular extension with a conical roof that houses the library of the Naval Observatory, while the west end houses a telescope tower for a 12-inch Alvan Clark refractor. The main section of the building and the library extension are covered with dressed stone with Greek classical details and the telescope end with rock-face stone with Egyptian details.
The Great Equatorial Building (renamed for astronomer Asaph Hall in 1966) is 46 feet wide and 72 feet long with one story and a basement with stone and brick walls. The historic 26-inch Alvan Clark refractor originally placed in operation in 1873 is in this building. In 1892, in preparation for the move to the new Naval Observatory, a new mounting was ordered from the Warner and Swasey Company in Cleveland, Ohio, for the sum of $28,700, since the original mounting design by Clark had been found to be too light. Warner and Swasey also built the 45-foot, 24-ton steel dome that surmounts the rough white Tuckahoe marble exterior of the building. The objective lens of the telescope was installed in June 1893 and the telescope was ready for regular observation by December. An elevator hardwood floor in the observing room moves up and down to facilitate the use of the telescope in different positions. The floor moves through a range of 12 feet from the lower to the upper balcony. It has to be near its lowest point when a star near the zenith is observed. In intermediate positions it can he quickly adjusted to any height from the eyepiece of the telescope.
No further major changes were made on the 26-inch refractor until 1958 when an overhaul and maintenance program was initiated. By 1964 the project had done away with the pier platform and its spiral access stairway and the auxiliary telescopes and periscopes which had been used for remote reading of the circles. Also, the mechanical fast and slow-motion rods and clamps were replaced by variable-speed clutches to transmit fast-motion power to the axes, synchro-systems with easily read console dials, and variable speed slow motions. The old clock drive was replaced with an electric one. A new tailpiece was added and an iris diaphragm installed ahead of the objective.
The Clock room is a one-story building 18 x 20 feet with a basement and stone and brick walls. For many years some of the most delicate clocks of the observatory were kept in this room. The clock room is at the exact center of the observatory circle.
The two Observers' rooms measure 18 x 20 feet and are found in a one-story frame building on a foundation of masonry.
The East Transit Circle and West Transit Circle buildings each measure 30 x 40 feet. Both structures are one-story buildings with iron frames on a foundation of masonry. The West Transit Circle building contains the six-inch meridian (transit) circle used exclusively for astrometry, with horizontal collimators, and north and south meridian marks. The instrument can be easily reversed to remove systematic errors in observations for determining the celestial latitudes of stars. Both circles are accurately divided. The instrument is provided with a motor driven micrometer. This telescope was designed by William Harkness of the observatory staff and built by Warner and Swasey, and mounted in 1897. The East Transit Circle building originally contained a 9-inch transit circle, modified from an older transit circle first used by Simon Newcomb. It was decommissioned in 1945 and was eventually replaced by a new 7-inch transit circle, designed and built at the Naval Observatory. The 7-inch transit circle was relocated to New Zealand in 1984 to begin astrometry observations in the southern hemisphere. Four small wooden structures (marker houses), used to align the transit telescopes, are found to the north of the East and West Transit Circle buildings and are considered to be part of these buildings.
The Boiler-house measures 45 x 54 feet and is a three-story building with stone and brick walls and is connected to the main building via a tunnel.
The Superintendent's House, designed by architect Leon Dessez, is a three-story brick structure with extensive use of dormers in the Queen Anne style. The house was originally used as the official residence of the Superintendent of the Naval Observatory. It is now used as the official residence of the Vice-President of the United States. No current information concerning this structure is available to the public.
The original brick carriage house and stable of the Barber estate, built around 1860, still stands. This building is a two-story brick L-shaped structure 88 feet x 68 feet x 31 feet with steep pitched roof Federal style windows and rooftop ventilating cupolas. The carriage house is now used by the Secret Service.
All other structures at the Naval Observatory, including the Simon Newcomb laboratory, gate houses, garages, greenhouses, storage buildings, dormitories and various maintenance facilities, are not part of this nomination and are not considered to contribute to the significance of the Naval Observatory as a National Historic Landmark.
The United States Naval Observatory is the oldest scientific institution in the Navy, being first established in 1830 as the Depot of Charts and Instruments. The observatory is most noted for its work in the study of positional astronomy and timekeeping. The Naval Observatory, along with the Royal Observatory in Greenwich, England, and the Pulkovo Observatory in the Soviet Union, is one of the few places in the world that continually observes and determines the positions of the sun, moon, planets, and stars. The United States Naval Observatory is the only place in the United States where precise instruments measure celestial motions to provide accurate time and other astronomical data which are essential for safe navigation at sea, in the air, and in space. 
The first attempts to establish a national astronomical observatory in the United States dates back to 1810 when the first proposals were introduced into Congress. In spite of strong support from such notables as Thomas Jefferson and John Quincy Adams, most Americans were reluctant to support funds for scientific research. When the Department of the Navy finally established the Depot of Charts and Instruments, celestial observations were needed to rate the chronometers stored there. Once begun, astronomical activities increased rapidly and by 1842, with the authorization of the first permanent buildings, the United States had a national observatory.
Until 1893 the observatory was located at 23rd and E Streets in Washington, DC. Under the leadership of Matthew Fontaine Maury, the Naval Observatory achieved wide acclaim for advances in astronomy, navigation, and oceanography. In the post-Civil War era leading mathematicians and astronomers such as Simon Newcomb, C. Henry Davis, George William Hill and Asaph Hall won world esteem. In 1877 for example, Asaph Hall used the historic 26-inch Alvan Clark Refractor at the Naval Observatory to discover the two moons of Mars--Phobos and Deimos.
By the early 1880s the location and facilities of the observatory were no longer suitable. In 1893 the observatory moved to a new site at 34th and Massachusetts Avenue with new buildings designed by architect Richard Morris Hunt. At this time the Nautical Almanac Office also became part of the Naval Observatory system.
Since 1893 the scientific research at the observatory has related primarily to timekeeping and to the determination, maintenance and dissemination of time, and to the determination of the fundamental celestial positions, motions and constants, which collectively comprise the field of astrometry. The United States Naval Observatory is the only institution in the United States where such fundamental observations are made on a regular basis. Scientists in the Nautical Almanac Office combine this data from the astrometry programs with the theories of motion of the solar system to compute the future positions of the sun, moon, and planets. This information, along with star positions, is made available to navigators, surveyors, geodesists, and astronomers, and forms the basis for all of their work. The Naval Observatory is the source of official time used in the United States and has been charged with maintaining the Department of Defense reference for precise time.
The fundamental work of the Naval Observatory in the study of astrometry cannot be overemphasized. This astronomical and timing data is essential for accurate navigation and the support of communications on Earth and in space, and is vital to both the Navy and the Department of Defense. This data is used for everything from guiding missiles to determining the distances to other galaxies and is used extensively by other governmental agencies and the public at large.
The Old Naval Observatory was made a National Historic Landmark in 1965, more than seventy years after the relocation of the observatory to the Massachusetts Avenue location. The designation of the 23rd and E Street site was based upon its association with Matthew Fontaine Maury, the father of modern oceanography, and leading astronomers and mathematicians such as Simon Newcomb, George William Hill and Asaph Hall, the discoverer of the two moons of Mars in 1877. The fundamental work of the New Naval Observatory since 1893 is in the specialized field of astrometry. For the past century the Navy has conducted astrometry observations from the same site using the same instruments. The period of time involved means that observations made today can be compared with observations made 10, 20 or even 90 years ago. By comparing modern observations with those taken years ago the Navy can accurately chart the positions of the stars and planets with a precision not available anywhere else in the United States. The site, the telescope, the buildings and even the weather patterns are the same. This accuracy of these observations forms a data base upon which the disciplines of astronomy, navigation, geodesy and surveying depend. It was in recognition of the importance of this work that the Congress originally moved the observatory to the Massachusetts Avenue site away from the traffic and congestion of Washington, and established a large boundary containing sufficient buffer land to protect the delicate instruments from the heat and vibrations arising from normal city traffic.
For many years the Naval Observatory has been regarded as the American National Observatory. By devoting its research to the science of astrometry, while other American observatories have studied more modern subjects, the Naval Observatory has earned a unique place in the history of American astronomy.
2. The material for the statement of significance was taken from the following sources:
Abell, George O. Exploration of the Universe. 4th ed., Philadelphia: Saunders College Publishing, 1982.
Asimov, Isaac. Eyes On The Universe. Boston: Houghton Mifflin Company, 1975.
Baker, Paul R. Richard Morris Hunt. Cambridge: Massachusetts, MIT Press, 1980.
Circular Relating to the Construction of a New Naval Observatory. Washington, D.C. : Navy Department, 1888.
Kirby-Smith, H.T. U.S. Observatories: A Directory and Travel Guide. New York, Van Nostrand Reinhold Company, 1976.
Learner, Richard. Astronomy Through the Telescope. New York: Van Nostrand Reinhold Company, 1981.
Marx, Siegfried, and Werner Pfau, Observatories of the World. New York: Van Nostrand Reinhold Company, 1984.
Rhynsburger, R. W. "A Historic Refractor's 100th Anniversary," Sky and Telescope. October 1973, pp. 2-8.
Schroer, Blanche H., and Steven H. Lewis, "National Register of Historic Places Inventory Nomination Form-Old Naval Observatory." Washington, DC: National Park Service, Historic Sites Survey Division, 1977.
"The New Naval Observatory, Washington, DC." The American Architect and Building News. October-December 1892, pp. 121-122.
United States Naval Observatory Washington, DC, U.S. Government Printing Office, 1982. (Brochure)
Warner, Deborah. "United States Naval Observatory," Astrophysics and twentieth century astronomy to 1950. Owen Gingerich, ed., Cambridge, England: Cambridge University Press, 1984.
Weber, Gustavus. The Naval Observatory: Its History, Activities and Organization. Baltimore: The Johns Hopkins University Press, 1926.
(click on the above photographs for a more detailed view)