7.5 Parallaxes Again
137
nomical Laboratory at Groningen 11; this research was also briefly presented in
St. Louis.
However, it was clear that there was not enough information to take the
next step. Kapteyn began an extensive set of investigations into the distances
of stars, together with his assistants Willem de Sitter and his second PhD
student Herman Albertus Weersma (1877–1961) (see Fig. 7.9). He obtained
his PhD in 1908; although journalist and amateur astronomer Cornelis Easton
had obtained a PhD in 1903, Herman Weersma was only Kapteyn’s second
student, since Easton’s degree was awarded honoris causa. Weersma’s work was
largely based on plates by Anders Donner. Among other things he tried to
measure parallaxes in star clusters, such as the double cluster h and χ Persei
with Anders Donner and Willem de Sitter and the nearby cluster Hyades with
Donner. In these and other fields, measurements were also made and studies
conducted on individual stars.
Fig. 7.9 Herman Albertus Weersma. 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]
137
nomical Laboratory at Groningen 11; this research was also briefly presented in
St. Louis.
However, it was clear that there was not enough information to take the
next step. Kapteyn began an extensive set of investigations into the distances
of stars, together with his assistants Willem de Sitter and his second PhD
student Herman Albertus Weersma (1877–1961) (see Fig. 7.9). He obtained
his PhD in 1908; although journalist and amateur astronomer Cornelis Easton
had obtained a PhD in 1903, Herman Weersma was only Kapteyn’s second
student, since Easton’s degree was awarded honoris causa. Weersma’s work was
largely based on plates by Anders Donner. Among other things he tried to
measure parallaxes in star clusters, such as the double cluster h and χ Persei
with Anders Donner and Willem de Sitter and the nearby cluster Hyades with
Donner. In these and other fields, measurements were also made and studies
conducted on individual stars.
Fig. 7.9 Herman Albertus Weersma. 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]