USNO-A2.0星表

USNO-A2.0 is a catalog of 526,280,881 stars, and is based on a re-reduction of the Precision Measuring Machine (PMM) scans that were the basis for the USNO-A1.0 catalog. The major difference between A2.0 and A1.0 is that A1.0 used the Guide Star Catalog (Lasker et al. 1986, see Cat. I/220) as its reference frame whereas A2.0 uses the ICRF as realized by the USNO ACT catalog (Urban et al. 1997, see Cat. II/246>).美国海军天文台A2.0星表（USNO-A2.0）是包含526,280,881颗恒星的星表，其基于对精密测量机（Precision Measuring Machine，PMM）扫描数据的再归算，而这些扫描数据正是美国海军天文台A1.0星表（USNO-A1.0）的制作基础。A2.0与A1.0的主要差异在于：A1.0以导星星表（Guide Star Catalog，Lasker等人1986年，详见星表Cat. I/220）作为其天球参考架，而A2.0则采用由美国海军天文台ACT星表（USNO ACT catalog，Urban等人1997年，详见星表Cat. II/246）所实现的国际天球参考架（ICRF）。