1 Instruction

The Chinese Photoelectric Astrolabe Mark I (PHA I) was improved significantly in 1994. One of the most important changes was to replace the old prism of $30^\circ$ zenith distance by a new $45^\circ$ prism. The structure and material of the new prism are the same as that of PHA II. It will offer a stable zenith distance of almucantar [5, (Xu et al. 1993)]. The observation of an astrolabe working at almucantar with zenith distance of $45^\circ$ at high latitude (such as Irkutsk, $\varphi=52\hbox{$.\!\!^\circ$}2$) can give a continuous declination system, besides right ascension system [, (Li et al. 1983]; [6, Xu et al. 1998)].

The PHA I was moved to the astronomical base of VS NIIFTRI in Irkutsk, Russia ($\varphi=52\hbox{$.\!\!^\circ$}2$) in Nov. 1995. From Nov. 1995 to June 1997, 200 stars were observed with PHA I. The data were reduced and a catalog named SIPA1 was compiled. SIPA1 covers 65 degrees of declination (from $9\hbox{$.\!\!^\circ$}6$ to $74\hbox{$.\!\!^\circ$}4$), which is the first astrolabe catalog without a blind zone in declination [6, (Xu et al. 1998)].

The internal errors of SIPA1 have been estimated by [6, Xu et al. (1998)]. What is the behavior of its systematic errors? It is important for us to assess the performance of PHA I and its future application. In this paper, the systematic errors of SIPA1 are analysed with the Hipparcos Catalog [2, (ESA, 1997)] as reference system. After removing the systematic errors, it is found that the precision of SIPA1 is comparable to the most accurate meridian observations.