9.6 The Solar Union Congress, 1910
195
twenty astronomers slept in tents because there was not room for everyone in
the hotel.
The congress started on Wednesday and lasted until Friday. George Hale
was only present on the first day because of his health. On Wednesday and
Thursday evening there were special lectures; Kapteyn took care of Wednesday’s
lecture. He talked about the research he was doing at that time and concerned
the distribution of what he called ‘helium stars’. I will discuss Kapteyn’s work
later.
The Solar Union conference ended with the return from the top of Mount
Wilson to Pasadena. It took considerably less time than the trip up (it took now
only about four hours) and in the evening there was a big dinner, offered by
George Hale and his wife, with over a hundred persons, conference participants
and special guests. It turns out that most of the participants, since they were
in California anyway, took the opportunity to visit the Lick Observatory, just
south of San Francisco. The European participants at the conference on Mount
Wilson must have been away from home from early August to early October.
9.7 Results of the Visits to Mount Wilson
The annual trips of the Kapteyns to California have been of great importance.
In the first place for the work on the Plan of Selected Areas, and in particular
the exposing of plates of all (eventually 139) northern Selected Areas that were
observable from Mount Wilson. The first few years were necessary to prepare
the whole thing; most of the photographic plates were taken between 1910 and
1912. The staff members Harold Delos Babcock (1882–1968) and Edward
Arthur Fath (1880–1959) took the plates. The most important staff member,
however, was the aforementioned Frederick Seares (Fig. 9.18). His share was
much more than just the coordinating of the work when Kapteyn was not on
Mount Wilson. In the end the work had to result in a catalog of all stars that
were visible (as faint as possible, and that was ultimately magnitude 18.5, so
one hundred thousand times fainter than the naked eye can see), with accurate
positions and apparent magnitudes (brightnesses).
A number of special problems arose. A giant telescope like the 60 in., which
was the largest in the world at the time, had serious imperfections in imaging
outside the center of the focal plane. That is because for a good image the
mirror had to be parabolic, which only worked properly exactly in the center
of the field being photographed. Just next to the ‘optical axis’ the images are
of poorer quality and corrections are required to derive the magnitudes of the
stars from the photographic plate. This turned a much bigger problem than
195
twenty astronomers slept in tents because there was not room for everyone in
the hotel.
The congress started on Wednesday and lasted until Friday. George Hale
was only present on the first day because of his health. On Wednesday and
Thursday evening there were special lectures; Kapteyn took care of Wednesday’s
lecture. He talked about the research he was doing at that time and concerned
the distribution of what he called ‘helium stars’. I will discuss Kapteyn’s work
later.
The Solar Union conference ended with the return from the top of Mount
Wilson to Pasadena. It took considerably less time than the trip up (it took now
only about four hours) and in the evening there was a big dinner, offered by
George Hale and his wife, with over a hundred persons, conference participants
and special guests. It turns out that most of the participants, since they were
in California anyway, took the opportunity to visit the Lick Observatory, just
south of San Francisco. The European participants at the conference on Mount
Wilson must have been away from home from early August to early October.
9.7 Results of the Visits to Mount Wilson
The annual trips of the Kapteyns to California have been of great importance.
In the first place for the work on the Plan of Selected Areas, and in particular
the exposing of plates of all (eventually 139) northern Selected Areas that were
observable from Mount Wilson. The first few years were necessary to prepare
the whole thing; most of the photographic plates were taken between 1910 and
1912. The staff members Harold Delos Babcock (1882–1968) and Edward
Arthur Fath (1880–1959) took the plates. The most important staff member,
however, was the aforementioned Frederick Seares (Fig. 9.18). His share was
much more than just the coordinating of the work when Kapteyn was not on
Mount Wilson. In the end the work had to result in a catalog of all stars that
were visible (as faint as possible, and that was ultimately magnitude 18.5, so
one hundred thousand times fainter than the naked eye can see), with accurate
positions and apparent magnitudes (brightnesses).
A number of special problems arose. A giant telescope like the 60 in., which
was the largest in the world at the time, had serious imperfections in imaging
outside the center of the focal plane. That is because for a good image the
mirror had to be parabolic, which only worked properly exactly in the center
of the field being photographed. Just next to the ‘optical axis’ the images are
of poorer quality and corrections are required to derive the magnitudes of the
stars from the photographic plate. This turned a much bigger problem than