This
number is too great to allow of all the stars being studied
individually; yet, to form the basis for any conclusion, we must
know the positions and arrangement of as many of them as we can
determine.
To do this the first want is a catalogue giving very precise
positions of as many of the brighter stars as possible. The
principal national observatories, as well as some others, are
engaged in supplying this want. Up to the present time about
200,000 stars visible in our latitudes have been catalogued on
this precise plan, and the work is still going on. In that part of
the sky which we never see, because it is only visible from the
southern hemisphere, the corresponding work is far from being as
extensive. Sir David Gill, astronomer at the Cape of Good Hope,
and also the directors of other southern observatories, are
engaged in pushing it forward as rapidly as the limited facilities
at their disposal will allow.
Next in order comes the work of simply listing as many stars as
possible. Here the most exact positions are not required. It is
only necessary to lay down the position of each star with
sufficient exactness to distinguish it from all its neighbors.
About 400,000 stars were during the last half-century listed in
this way at the observatory of Bonn by Argelander, Schonfeld, and
their assistants.
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