To link the optical reference frame to extragalactic radio frame, an observation program is in progress in Purple Mountain Observatory (PMO) and Shanghai Observatory. In this program, 70 extragalactic sources will be observed with the 1.56 m astrometric reflector in Shanghai. The secondary reference stars are determined with the twin astrograph (D = 40 cm, f = 300 cm) in PMO, and about 50 radio stars and some bright extragalactic sources will be observed with the twin astrograph.

Measurements of precise positions of optical counterparts of extra-galactic radio-sources, with the aim to compare them with VLBI positions, is in progress at Torino Observatory. The Carlsberg Automatic Meridian Circle Catalogue (CAMC) is used for plate reductions. Presently, about 40% of the plate material required to complete the project has been taken and some significant improvements have been made both in the material and the reduction methods. Improvements are also due to the publication of a new volume of the CAMC catalogue that significantly increases the number of stars in the fields.

The right ascension of the radio source 3C273B, which serves as a right ascension zero point in radio astrometric work, has been determined from lunar occultations and photographic observations.

We re-analyze here the lunar occultations of 3C273B using the recent precise lunar ephemeris and obtain its right ascension referred to the FK5 equinox at J2000.0. The obtained right ascension is 12h29m06s.6946±0s.007 at its mean observation epoch of 1963.62.

Predictions of occultations of radio sources by the Moon and planets are also given. Observations of them are encouraged in order to improve the accuracy of the linkage between radio and stellar reference frames.

The positions of radio stars measured with respect to the VLBI network of extragalactic sources provides an important link between the optical and extragalactic reference frames. The establishment of this link was brought a stage nearer realization with the publication by Florkowski et al.(1985) of the radio positions of 20 stars measured with the Very Large Array (VLA) of the National Radio Astronomy Observatory, and the publication by Lestrade et al.(1985, 1988) of 10 stars measured with the VLBI network.

The procedure of construction of special compiled catalogue is presented. The compiled catalogue is based on 6 catalogues obtained following the KSZ plan. The mean error of proper motions of stars is ±0.″009 per year. AGK3 proper motions compared with those in the compiled catalogue yield precession corrections Δk=-0.″0046 ± 0.″0010, Δn = +0.″0045 ± 0.″0010. Systematic differences between these catalogues are represented by a series development using products of Hermite polynomials, Legendre polynomials and Fourier terms.

The U.S. Naval Observatory has commissioned the fabrication of an array of six charge-coupled devices (CCDs) bonded to a single silicon substrate for precision astrometry of sources spanning a large range in apparent brightness. The array includes one CCD with rapid readout capability for imaging bright stars. We present the design parameters and the anticipated performance characteristics of this sensor.

The features of the astrolabe are that:

(1) a span of 6 hour of R.A. of star positions can be tied in a group of observation of 2 hours, all-night observation can cover more than half of the sky, and

(2) the declination system can be set up with high precision without the need of a precise circle (Li 1987).