According to the latitude of the astrolabe ), a zone comprised
between
and
in declination can be observed at
zenith
distance from Santiago. A zone around the southern celestial pole of
about
wide in declination is not observable since in this zone the
small declination circles of the stars do not intercept the
almucantar. The observational program at
zenith distance consists
of eleven groups of 28 stars each one. The star distribution in
azimuth in each group is as uniform as possible. The eleven groups
comprise 166 FK5 and 103 FK5 Extension stars. Of these 269 stars, 39
are observed in double transit. The observations were reduced
following the IAU76/82 resolutions on fundamental constant and
apparent places computation (Kaplan 1981;
Chollet 1984). At
zenith
distance the stars images as observed with the astrolabe, show
permanently a rather strong agitation due to atmospheric effects. The
effect of the image agitation on the results is clearly reflected in
the precision of the mean zenith distance residuals of the stars. They
were obtained with an average mean error of
, which is more or
less twice the average mean error obtained at Santiago from
observations at
zenith distance
(Noël & Débarbat 1990).