196
9 Mount Wilson
Fig. 9.18 Frederick Hanley Seares. This picture comes from the Album Amicorum, presented to H.G. van de Sande Bakhuyzen on the occasion of his retirement as professor
of astronomy and director of the Sterrewacht Leiden in 1908 [47]
with the smaller refractor telescopes for example as used for the CPD and
the like. It was mainly thanks to Frederick Seares that these corrections could
be made. Furthermore, the brightness and positions had to be uniform and
consistent within and among each of the Selected Areas. In order to measure
bright stars consistently with the fainter ones, exposures had to be taken in
which either the exposure time was shorter or part of the mirror was covered
with an aperture. Seares, together with staff member Harlow Shapley, recorded
special plates for this purpose between 1913 and 1919. Also, the magnitudes
between different Selected Areas had to be consistent and related to a set of
standard stars around the North Pole (which were visible all year round from
Mount Wilson). This was done by recording both a Selected Area and this