You are here: Home USNO

The United States Naval Observatory (USNO)

3450 Massachusetts Ave, NW, Washington, DC 20392-5420
Urania Clear

The United States Naval Observatory (USNO) provides a wide range of astronomical data and products, and serves as the official source of time for the U.S. Department of Defense and a standard of time for the entire United States.

USNO products support activities in the following areas:


Integrated Image and Catalog Archive Service, star catalogs, fundamental reference frames, space astrometry.

Astronomical Applications

Astronomical data calculators (e.g., rise/set times, Moon phase, etc.), information on astronomical phenomena and related topics, astronomical and navigational almanacs, software products.

Earth Orientation

Daily, weekly, and long-term EO products (e.g. IERS Bulletin A), GPS-based products (rapids, ultra-rapids, UTGPS), VLBI-based products, background information, technical and scientific publications and software.

Precise Time

USNO Master Clock, Network Time Protocol (NTP) servers, web-based time synchronization, GPS timing products and services, Two-Way Satellite Time Transfer, and Loran-C timing products.

The James M. Gilliss Library

USNO's library holds one of the most complete collections of astronomical literature in the world.

Tours & Events

Information on tours of the Naval Observatory, upcoming scientific colloquia, and other events.

About Us

Information about the U.S. Naval Observatory.


USNO Master Clock Time
Javascript must be Enabled