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The NOMAD Catalog

The U. S. Naval Observatory is pleased to announce the first release of the Naval Observatory Merged Astrometric Dataset (hereafter referred to as NOMAD). NOMAD is a simple merge of data from the Hipparcos, Tycho-2, UCAC-2 and USNO-B1 catalogues, supplemented by photometric information from the 2MASS final release point source catalogue. The primary aim of NOMAD is to help users retrieve the best currently available astrometric data for any star in the sky by providing these data in one place.

Access to NOMAD

Documents describing NOMAD



  • ReadMe file describing NOMAD
  • Description of the details of the data columns in NOMAD
  • Abstract of the paper given at the January 2005 AAS meeting held in San Diego, CA.
  • Poster describing NOMAD given at the January 2005 AAS meeting (PDF format).
  • Links to information about the various catalogues used in making NOMAD

Abstract of the paper given at the January 2005 AAS meeting held in San Diego, CA. This poster paper was meant to announce the availability of NOMAD, and to briefly describe the characteristics of the new dataset.

Title: The Naval Observatory Mergered Astrometric Dataset (NOMAD)

Authors: Norbert Zacharias, Dave Monet, Stephen Levine, Sean Urban, Ralph Gaume, and Gary Wycoff

Abstract: The U.S. Naval Observatory (USNO) releases the first version of the Naval Observatory Merged Astrometric Dataset, NOMAD. The 100 GB dataset contains astrometric and photometric data for over 1 billion stars. Its source catalogs are primarily Hipparcos, Tycho-2, UCAC2, and USNO-B for astrometry and optical photometry, supplemented by 2MASS near-infrared photometry. For each unique star the "best" astrometric and photometric data are chosen from the source catalogs following a sequence of priorities based on the source catalogs' accuracies within a particular magnitude range. NOMAD contains flags to identify the source catalogs and gives cross-reference identifications. For this first release, NOMAD is not a compiled catalog; that is, if a star is identified in more than 1 of the above mentioned catalogs, only 1 catalog entry is chosen. Thus the local and global systematic errors of the various source catalogs will be present in this version. All astrometric data is on the International Celestial Reference System within the limitations of the source catalogs. NOMAD can be retrieved from a NOFS server through a web interface which includes detailed user information (

Details for the various primary catalogues that have been included in NOMAD can be found at the following locations:

Catalogue Access
Monet, D. et al. 2003, AJ, 125, 948 (in PDF)
Column Documentation

Last updated: 2008Dec12 by sel
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