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Contents of Bulletin A
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General Information about Earth Orientation
Frequently Asked Questions About Earth Orientation
What Is Earth Orientation?
What Is Polar Motion?
What does the Earth rotation coordinate measure?
What is the Celestial Pole Offset?
What is a Leap Second?
How do we measure Earth Orientation?
What causes variations in the Earth's orientation?
Who uses Earth orientation information?
Publications About Earth Orientation Products
Earth Orientation Software
Precise Time Department
The USNO Master Clock
The USNO Master Clock
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USNO Alternate Master Clock (AMC)
Cesium Atomic Clocks
Hydrogen Masers at the USNO
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International Time Scales and the BIPM
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Global Positioning System
Global Positioning System Overview
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CGGTTS Data Format
USNO GPS Time Transfer
GPS Information: SA, DGPS, Leap Seconds, etc.
GPS Week Number Rollover
GPS Timing Data and Information
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United States Naval Observatory
The Naval Observatory Flagstaff Station
Established in 1955 a few miles west of Flagstaff, Arizona, the Flagstaff station is the US Naval Observatory's dark-sky site for optical and near-infrared astronomy. There are presently two USNO sites in the Flagstaff area: this station (NOFS) and the Navy Precision Optical Interferometer (NPOI) located some 15 miles south of the city at the Lowell Observatory's Anderson Mesa site.
A Brief History of NOFS
In 1946 the U.S. Congress authorized funding for a new Washington Hospital Center, to be built on land ceded from another Federal agency within the District of Columbia. In 1947 SECNAV James Forrestall was informed that the USNO's Georgetown campus had been selected and the property had to be vacated as quickly as possible, ideally within a month. Spearheading this effort was Senator Millard E. Tydings of Maryland, chairman of the Senate Military Affairs Committee, whose wife served on the site selection committee for the hospital.
After much wrangling with the Senator's staff, USNO astronomers succeeded in getting a "stay" of one year to select a new site and to maintain the continuity of observations made from Washington over the previous 100+ years. Several sites were proposed, including Flagstaff, Arizona, home of the Lowell Observatory, but ultimately a site near Charlottesville, Virginia was chosen. In 1950 an appropriation of $7 million was passed by Congress to facilitate the move, but in that year's general election Senator Tydings was defeated and plans to move the Observatory were shelved.
However, site testing at the various proposed locations showed that a 7,600-foot hill five miles west of Flagstaff had excellent sky conditions, and in 1955 the
40-inch Ritchey-Chretien reflector telescope
was moved to that site, where its full potential, previously hampered by the sky conditions in Washington, was finally realized.
By 1957 the idea of building a large telescope for measuring the parallaxes of faint nearby stars began to take root. In 1958 Dr. Kaj Strand joined the Observatory staff and worked diligently to oversee the fruition of that idea. Based at the Flagstaff site, the new telescope, a
reflector of 1.55-meter (61-inch) aperture
, would be able to photograph very faint stars far beyond the reach of the classical refractors used up to that time. In October 1959 funds were appropriated to begin construction, and the new telescope was dedicated in June, 1964. The telescope, now named in honor of Dr. Strand, continues to be the centerpiece of the telescopes at NOFS.
Several other telescopes now share the dark skies over the Flagstaff Station. An
8-inch transit circle
, now completely automated, makes nightly observations of planetary satellites, minor planets, and selected star fields where precise astrometry of those objects is required. A
, optimized for wide-field infrared detection, is used to look for faint sub-luminous stars and "brown dwarfs". An 8-inch astrograph capable of imaging large areas of the sky in visible light has completed two major star catalogs with observations made at NOFS and the Cerro Tololo Inter-American Observatory (CTIO) in Chile.
A 1.8-meter telescope is currently under construction at NOFS. It will work in tandem with an identical telescope in Australia to measure astrometric properties of stars in both hemispheres of the sky. It is expected to begin operation in 2022.
NOFS staff support the operation of the
Navy Precision Optical Interferometer (NPOI)
sited at Lowell Observatory's Anderson Mesa station located about 15 miles south of Flagstaff.
The City of Flagstaff has been an enthusiastic supporter of astronomical research within its city limits. It has been designated as the world's first (and so far only) International Dark Sky City by the
International Dark Sky Association (IDA)
. USNO works diligently with the city and IDA to maintain the pristine skies over its facility at NOFS.
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