All the observations were made visually by the author of this paper and
each one consists in timing the transit of one border of the Sun through
the corresponding small circle of fix altitude. During one day
one observes the transits of the upper and lower border at the east,
and the transits of the lower and upper border at the west. The fix
zenith distances of and
are defined by means of CERVIT
reflecting prism that are interchangeable rather easily in a few minutes
without further adjustment of the telescope. Therefore, observations at
at both zenith distances are possible during the same day. According to
the latitude of the astrolabe (
) the Sun
can be observed during the whole year at
zenith distance and
from October 6 untill March 7 at
.
The transit times are registered by a PC microcomputer adapted as
chronograph with resolution. The precise UTC reference
is provided by a GPS timer receiver at the astrolabe pavillion, or
alternatively, by a Cesium atomic standard of the time service of
Cerro Calán Observatory.
Copyright The European Southern Observatory (ESO)