United States Naval Observatory Flagstaff Station - General Information

General Information

The USNO and NOFS are commands within the CNMOC claimancy, the latter which serves the U.S. Navy on meteorological and oceanographic matters in addition to overseeing astronomical ones. The Flagstaff Station is a command which was established by USNO (due to a century of eventually untenable light encroachment in Washington, D.C.) at a site five miles west of Flagstaff, Arizona in 1955, and has positions for 35 scientists (astronomers and astrophysicists), optical and mechanical engineers, and support staff. It is currently manned at 20 personnel. Its principal mission is to provide the military and others extremely accurate, ground-based astrometry (defined as the positions of celestial and artificial space objects), Celestial mechanics (dynamical motions of celestial objects) and photometry (defined as brightness variations, often in terms of 'color') – in the form of million-to-billion-star catalogs for a wide diversity of U.S. global (and spaceborne) position and navigation interests. NOFS specializes in extremely faint-magnitude, extremely accurate observations which cannot normally be obtained from space telescopes, and remains the most respected astrometric observatory in the world. NOFS remains the senior U.S. Navy facility/unit in the state of Arizona.

NOFS science supports every aspect of protection-oriented operations to some level, providing national support and beyond. Work at NOFS covers the gamut of astrometry and astrophysics in order to facilitate its production of very accurate/precise astronomical catalogs, such as USNO-B, NOMAD, and others delivered by NOFS. Astrometry for such catalogs (producing a "celestial reference frame" (CRF), such as the ICRF is), requires handling terabytes of diverse data on a billion or more celestial objects, all the while accurately characterizing the centroids of the point spread functions (PSFs) of each object in that vast database, including pinning down positions of innumerable, diverse types of objects. Such diversity severely complicates how to dynamically determine where many of the large collections of celestial objects really 'are'. Complete catalogs require much study of binary/multiple, flare, oblate, starspot-laden stars, and astrometrically extended objects, in addition to the classically 'simple', spheroidally shaped single stars. Many of these types of "problem stars" (and their oddly shaped cousins) proliferate much of the night sky, so must have some accounting, in large major catalogs. Characterizing the astrophysical diversity, so as to know the objects' positions, helps to determine how up to a billion positions can be made accurate to perhaps to a few, critical milli-arcseconds, to provide an accurate faint—or bright – "background", upon which users may reference their own critical work. As well, users may need a large collection of just the brighter magnitude stars, or the much fainter ones (much more difficult to assess), or both. Users may also require a catalog suited to blue or red optical, near or far (or thermal) infrared, or millimeter/microwave/radio portions of the electromagnetic spectrum. This matches the user's need for a background similar to their observational interests. In astrometry, the PSFs of the stars' centroids vary significantly from one bandpass to another, so must be atoned for in catalog development. Faint star densities are almost exponentially more numerous in a given patch of sky, so faint catalogs will require much more effort to produce for the user.

Also, owing to the celestial dynamics (and relativistic effects) of the huge number of such moving objects across their own treks through space, the time expanse required to pin down each set of celestial locations and motions for a perhaps billion-star catalog, can be quite long. Multiple observations of each object may themselves take weeks, months or years, by themselves. This, multiplied by the large number of cataloged objects that must then be reduced for use, and which must be analyzed after observation for a very careful statistical understanding of all catalog errors, forces the rigorous production of most extremely precise and faint astrometric catalogs to take many years, sometimes decades, to complete.

Because stars move, both due to their own wanderings (proper motions) throughout space, and due to the observer's Earth orientation movements (such as precession, nutation, parallax, geophysical and tidal variations), a catalog's accuracy slowly but progressively degrades in increased error over time, beginning the moment after the sky is imaged for cataloging. The degrading motions 'confuse' observations with motions which astrometrists are usually not able to completely constrain despite extensive scientific modeling and deliberation. So eventually a whole new catalog must be produced when a user's needs for given accuracies force a new, updated catalog, for some later epoch. One remedy to break such a daunting cycle is to maintain an ongoing input and updating process, which makes the common operational picture (COP) produced by such a dynamic catalog, a more efficient and timely means to delver such large quantities of changing data to the variety of users. NOFS has a key program (awaiting funding) called the Dynamic Astrometric Database (DyAD) which will operate under the near real-time ("on-the-fly") paradigm.

While principally responsible for the internal faint-star astrometric reference frame, NOFS scientists also externally develop an improved understanding of celestial goings-on, by participating on many science teams and in relevant collaborations. Institutions NOFS works with include DARPA, NASA, NRL, MIT, NRAO, Smithsonian, GEODSS, Los Alamos National Laboratory (LANL), AMOS, USNA, Air Force Space Command, Lowell Observatory, NOAO, AAS, IAU, and many other academic and DoD institutions. Staff Astronomers observe both on local telescopes and at other observatories around the globe—using both terrestrial, interferometric and spaceborne instrumentation.

The NOFS staff is organized into four divisions: Optical/Infrared, Engineering & Site Operations, Digital Catalogs, and Navy Precision Optical Interferometer(NPOI) Divisions. Additional management staff members serve executive, IT (computer LAN/systems), fiscal, administrative, and facilities functions.

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NOFS is the U.S. Navy's National Dark Sky Site, and is responsible for the bulk of the 'astrometric component' of the U.S. DoD and national Position-Navigation-Time (PNT) mission.

The United States Naval Observatory, Flagstaff Station celebrated its 50th anniversary of the move there from Washington, D.C. in late 2005. Each autumn, NOFS opens its doors annually to the public, during the Flagstaff Festival of Science. In 2009, visitor attendance topped 710.

Dr. John Hall, Director of the Naval Observatory's Equatorial Division from 1947, founded NOFS. Dr. Art Hoag became its first director in 1955 (until 1965); both later were to also become directors of nearby Lowell Observatory. Subsequent directors at NOFS include (in order): 2nd – Dr. Gerald Kron (1965–1973); 3rd – Dr. Harold Ables (1974–1995); 4th – Dr. Conard Dahn (1996–2003); 5th – Dr. Jeff Pier (2003–2008); and 6th – Dr. Paul Shankland (2008–present).

NOFS remains active in supporting regional dark skies, both to support its national protection mission, and to promote and protect a national resource legacy for generations of humans to come.