An official website of the United States government
Here's how you know
Official websites use .mil
website belongs to an official U.S. Department of Defense organization in the United States.
Secure .mil websites use HTTPS
means you’ve safely connected to the .mil website. Share sensitive information only on official, secure websites.
Skip to main content (Press Enter).
Official Website of the United States Navy
Mission & Vision
Naval Oceanographic Office
Fleet Numerical Meteorology & Oceanography Center
United States Naval Observatory
News from the Naval Observatory
Earth Orientation Department
USNO Earth Orientation Products
Contents of Bulletin A
USNO GPS Products
GPS User Information
USNO VLBI-based Products
VLBI Correlator Data
VLBI-based Earth Orientation Parameters (EOP)
Earth Orientation Information Center
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
Time Dissemination at the USNO
USNO Alternate Master Clock (AMC)
Cesium Atomic Clocks
Hydrogen Masers at the USNO
Rubidium Fountain Clocks
USNO Time Scales
International Time Scales and the BIPM
Definitions of Systems of Time
Global Positioning System
Global Positioning System Overview
USNO GPS Data Categories Explanation
CGGTTS Data Format
USNO GPS Time Transfer
GPS Information: SA, DGPS, Leap Seconds, etc.
GPS Week Number Rollover
GPS Timing Data and Information
USNO Format Explanation
USNO Computer Display Clocks
Two-Way Satellite Time Transfer (TWSTT)
Network Time Protocol (NTP)
US Eastern Time Zone NTP Servers
US Mountain Time Zone Servers
DoD Customer Servers
Astronomical Applications Department
Celestial Reference Frame Department
Senior Enlisted Advisor
Naval Oceanography Operations Command
Fleet Weather Center - Norfolk
Fleet Weather Center - San Diego
Joint Typhoon Warning Center
Public Use of Limitations
United States of America Department of the Navy Seal
celestial reference frames department
is the branch of astronomy concerned with the determination of positions, proper motions, and parallaxes of solar-system bodies, stars, and distant galaxies. Astronomers in the Celestial Reference Frame Department use the latest instrumentation and methods to extend the accuracy and brightness limits of astrometric catalogs and reference frames.
Optical/infrared image and catalog products provided by the USNO. Astrometric catalogs include NOMAD, UCAC, USNO-B1, Double Stars, etc. Imaging products include digital scans of a number of the major Schmidt telescope surveys of the skies, along with the catalogs of astronomical objects created from those images. Access to astrometric catalogs and imaging products is provided through these pages.
Very Long Baseline Interferometry (VLBI) is a technique used by radio astronomers and geodesists to determine the celestial and terrestrial reference frames and to predict the variable orientation of the Earth in three-dimensional space. Access to VLBI images is available through the Radio Reference Frame Image Database.
DoD Accessibility/Section 508
No Fear Act
Plain Writing Act
Veterans Crisis Line
DoD Safe Helpline
Commander, Naval Meteorology and Oceanography Command | 1100 Balch Blvd. | Stennis Space Center, Mississippi 39529
Official U.S. Navy Website