4.1 The Sterrewacht Leiden
51
of the telescope by thermal expansion, it was even shielded from the heat of
bodies: the observer himself and sometimes a colleague who made notes. Of
great importance was the difference between the temperature of the air in the
observation room and that outside. The roof was opened well on time around
sunset, but improvements had to be made to the observation room itself.
The director seized the opportunity to thoroughly refurbish the instrument
itself; for that it had to be disassembled and sent to the manifacturer, J.G.
Repsold and Sons in Hamburg. Before that could be done, everything had to
measured and documented, from the precise positions of the marks on the
reading scales to the characteristics of the threads in the positioning screws and
the telescopic tube’s stiffness. This was necessary in order to be able to make
any corrections to the fifteen-year-old archive of observations. The observators
did most of this work in practice, which was an excellent way for Kapteyn to
gain experience in astrometry and positional astronomy. Also much work with
regard to the determination of star positions continued. For example, there was
another possibility to measure the solar parallax, when Mars in 1877 would be
relatively close to the Earth during opposition. In opposition, a planet, Mars
in this case, is opposite the Sun from the Earth’s point of view and is therefore
as close as possible to the Earth. The planet will then be visible all night long.
The project required very accurate measurement of the relative positions of
stars in the Mars environment in the sky. And that had to be done at many
different observatories. At the Sterrewacht Leiden the meridian circle could
not be used, so other telescopes were used for this purpose.
In Leiden, Kapteyn made some friends for life. He had regular dinners
with a group of contemporaries, including the later famous botanist William
Burck (1848–1910) and Ambrosius Arnold Willem Hubrecht (1853–1915).
Hubrecht later became professor of zoology and anatomy in Utrecht and was
well-known for his work in embryology. He was a son of the Secretary General
of the Ministry of the Interior, which covered the universities, and therefore
he sometimes had some inside information. One evening Hubrecht ordered a
bottle of champagne and made a toast to Kapteyn’s brother, Willem, who had
been named a professor. This to Kapteyn’s surprise. And then Hubrecht ordered
a second bottle to make a toast to Kapteyn himself, who had been appointed
professor in Groningen. Both appointments had not even been announced
officially yet, but this happened shortly after in the Staatscourant of December
14, 1877 (see Fig. 1).
51
of the telescope by thermal expansion, it was even shielded from the heat of
bodies: the observer himself and sometimes a colleague who made notes. Of
great importance was the difference between the temperature of the air in the
observation room and that outside. The roof was opened well on time around
sunset, but improvements had to be made to the observation room itself.
The director seized the opportunity to thoroughly refurbish the instrument
itself; for that it had to be disassembled and sent to the manifacturer, J.G.
Repsold and Sons in Hamburg. Before that could be done, everything had to
measured and documented, from the precise positions of the marks on the
reading scales to the characteristics of the threads in the positioning screws and
the telescopic tube’s stiffness. This was necessary in order to be able to make
any corrections to the fifteen-year-old archive of observations. The observators
did most of this work in practice, which was an excellent way for Kapteyn to
gain experience in astrometry and positional astronomy. Also much work with
regard to the determination of star positions continued. For example, there was
another possibility to measure the solar parallax, when Mars in 1877 would be
relatively close to the Earth during opposition. In opposition, a planet, Mars
in this case, is opposite the Sun from the Earth’s point of view and is therefore
as close as possible to the Earth. The planet will then be visible all night long.
The project required very accurate measurement of the relative positions of
stars in the Mars environment in the sky. And that had to be done at many
different observatories. At the Sterrewacht Leiden the meridian circle could
not be used, so other telescopes were used for this purpose.
In Leiden, Kapteyn made some friends for life. He had regular dinners
with a group of contemporaries, including the later famous botanist William
Burck (1848–1910) and Ambrosius Arnold Willem Hubrecht (1853–1915).
Hubrecht later became professor of zoology and anatomy in Utrecht and was
well-known for his work in embryology. He was a son of the Secretary General
of the Ministry of the Interior, which covered the universities, and therefore
he sometimes had some inside information. One evening Hubrecht ordered a
bottle of champagne and made a toast to Kapteyn’s brother, Willem, who had
been named a professor. This to Kapteyn’s surprise. And then Hubrecht ordered
a second bottle to make a toast to Kapteyn himself, who had been appointed
professor in Groningen. Both appointments had not even been announced
officially yet, but this happened shortly after in the Staatscourant of December
14, 1877 (see Fig. 1).