Statistics of Astronomical Observing Conditions at the Xinlong Station Based on the Observing Logs from 1999 to 2008

Based on the observing logs of the last ten years, we carried out the statistics of the monthly variations of times usable for observation at the Xinglong station.The results show that there were about 195 nights(about 1986 hours)available for observation in one year, among which about 87 nights (about 918 hours) were used for the BATC survey and about 18 nights are for photometric measurements.We also carried out the statistics of the monthly variations of FWHMs of the images of stars in the North Pole region observed by the 60/90 Schmidt telescope, and found that the mean FWHM within a year is about 2.3 pixels of the old CCD or 2.2 pixels of the new CCD.Usually, star images are more clear in the summer than in the winter, which is consistent with the result of Liu 2003.