SEEING MEASUREMENTS AND OBSERVING STATISTICS AT THE UNITED-STATES-NAVAL-OBSERVATORY, FLAGSTAFF STATION

Direct measurements of the seeing for the U.S. Naval Observatory, Flagstaff Station are presented for the years 1986-1991 from the USNO CCD parallax program at the 1.55-m telescope. Cloud-cover and seeing-related statistics are presented for all programs from the same telescope for the years 1969-1990. The data show that seeing at the zenith has a median of 1.3 arcsec and a mode of 1.0 arcsec FWHM; the distribution of observed seeing probably includes a significant contribution from local dome seeing and/or telescope effects. Cloud-cover statistics show that a yearly average of approximately 45% of the nighttime hours are clear and 65% usable. Both the cloud-cover and seeing statistics show significant seasonal variations. The Flagstaff data are also compared with published statistics from Kitt Peak National Observatory.