F. Hill, P. B. Stark, R. T. Stebbins, E. R. Anderson, H. M. Antia, T. M. Brown, T. L. Duvall Jr., D. A. Haber, J. W. Harvey, D. H. Hathaway, R. Howe, R. P. Hubbard, H. P. Jones, J. R. Kennedy, S. G. Korzennik, A. G. Kosovichev, J. W. Leibacher, K. G. Libbrecht, J. A. Pintar, E. J. Rhodes Jr., J. Schou, M. J. Thompson, S. Tomczyk, C. G. Toner, R. Toussaint, W. E. Williams

The Global Oscillation Network Group (GONG) project estimates the frequencies, amplitudes, and linewidths of more than 250,000 acoustic resonances of the sun from data sets lasting 36 days. The frequency resolution of a single data set is 0.321 microhertz. For frequencies averaged over the azimuthal order m, the median formal error is 0.044 microhertz, and the associated median fractional error is 1.6 × 10⁵. For a 3-year data set, the fractional error is expected to be 3 × 10⁶. The GONG m-averaged frequency measurements differ from other helioseismic data sets by 0.03 to 0.08 microhertz. The differences arise from a combination of systematic errors, random errors, and possible changes in solar structure.

F. Hill, E. R. Anderson, J. W. Harvey, R. P. Hubbard, J. R. Kennedy, J. W. Leibacher, J. A. Pintar, C. G. Toner, R. Toussaint, and W. E. Williams are with the National Solar Observatory, National Optical Astronomy Observatories (NOAO), Post Office Box 26732, Tucson, AZ 85726-6732, USA. P. B. Stark is with the Department of Statistics and Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA. R. T. Stebbins and D. A. Haber are with JILA, University of Colorado, Boulder, CO 80309, USA. H. M. Antia is with the Tata Institute of Fundamental Research, Bombay, India. T. M. Brown and S. Tomczyk are with the High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO 80307, USA. T. L. Duvall is with the NASA Goddard Space Flight Center, Stanford University, Center for Space Science and Astrophysics (CSSA), Stanford, CA 94305, USA. D. H. Hathaway is with the NASA Marshall Space Flight Center, Mail Code ES82, Huntsville, AL 35812, USA. R. Howe and M. J. Thompson are with the Astronomy Unit, Queen Mary and Westfield College, London E1 4NS, UK. H. P. Jones is with the NASA Goddard Space Flight Center Southwest Station, NOAO, Tucson, AZ 85726, USA. S. G. Korzennik is with the Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA. A. G. Kosovichev and J. Schou are with Stanford University, CSSA, Stanford, CA 94305, USA. K. G. Libbrecht is with the California Institute of Technology, 264-33, Pasadena, CA 91125, USA. E. J. Rhodes is with the Department of Physics and Astronomy, University of Southern California, Los Angeles, CA 90089, USA.