136
7 Star Streams
On their return journey they visited Newcomb in Washington, where they would
also attend the big reception at the White House. They rode in Newcomb’s
equipage with two horses and black palfrenier, and were introduced to president
Roosevelt at the same time as Hugo de Vries, who was also in Washington then.
He had an appropriate word and a handshake for each of them: ‘Ah Mr. de Vries
– I suppose we are cousins, because the name de Vries is in my family.’ This, of
course, with the necessary pride, because Dutch names meant status in America.
For Kapteyn he had a friendly remark about astronomy, and also this remarkable
moment belonged to the past.
7.5 Parallaxes Again
The discovery of the Star Streams was a serious problem for the program that
Kapteyn had devised to determine the spatial distribution of the stars. Of
course he did not have to give it up completely, but it all became much more
complicated. The next steps were the following. In the first place there had to
be counts to much fainter magnitudes than previously available. Furthermore,
measurements of as many parallaxes and proper motions as possible, and of
course a better determination of both the position of the Apex of the Sun and
its spatial velocity, and in addition now also the direction and velocities of the
Star Streams. And it became more and more clear that stars among themselves
had very different properties, which were not yet understood, but this had to
be determined.
In Publications of the Astronomical Laboratory at Groningen number 8,
Kapteyn had determined as well as was possible the average parallax of stars
as a function of apparent magnitude and proper motion. With this statistical
estimate of stellar distances he was able to make a rough estimation of the
distribution of stars in space and that resulted in 1901 in a first estimation of
the run of star density with distance from the Sun. During a lecture for the
Netherlands Academy of Sciences, he presented it for the first time. First he
determined the ‘luminosity curve’, which he had assumed was the same everywhere, and using that the density of stars. What became clear was that the
stellar density decreased as one moved away from the Sun. It was known that
stars had very different spectra and could therefore differ significantly from
one another in luminosity. In 1901 this had not yet been properly determined,
but Kapteyn divided the stars into two main groups and did a first, very preliminary investigation into how the laws of brightness and density depended
on this. He published this first attempt a year later in Publications of the Astro-
7 Star Streams
On their return journey they visited Newcomb in Washington, where they would
also attend the big reception at the White House. They rode in Newcomb’s
equipage with two horses and black palfrenier, and were introduced to president
Roosevelt at the same time as Hugo de Vries, who was also in Washington then.
He had an appropriate word and a handshake for each of them: ‘Ah Mr. de Vries
– I suppose we are cousins, because the name de Vries is in my family.’ This, of
course, with the necessary pride, because Dutch names meant status in America.
For Kapteyn he had a friendly remark about astronomy, and also this remarkable
moment belonged to the past.
7.5 Parallaxes Again
The discovery of the Star Streams was a serious problem for the program that
Kapteyn had devised to determine the spatial distribution of the stars. Of
course he did not have to give it up completely, but it all became much more
complicated. The next steps were the following. In the first place there had to
be counts to much fainter magnitudes than previously available. Furthermore,
measurements of as many parallaxes and proper motions as possible, and of
course a better determination of both the position of the Apex of the Sun and
its spatial velocity, and in addition now also the direction and velocities of the
Star Streams. And it became more and more clear that stars among themselves
had very different properties, which were not yet understood, but this had to
be determined.
In Publications of the Astronomical Laboratory at Groningen number 8,
Kapteyn had determined as well as was possible the average parallax of stars
as a function of apparent magnitude and proper motion. With this statistical
estimate of stellar distances he was able to make a rough estimation of the
distribution of stars in space and that resulted in 1901 in a first estimation of
the run of star density with distance from the Sun. During a lecture for the
Netherlands Academy of Sciences, he presented it for the first time. First he
determined the ‘luminosity curve’, which he had assumed was the same everywhere, and using that the density of stars. What became clear was that the
stellar density decreased as one moved away from the Sun. It was known that
stars had very different spectra and could therefore differ significantly from
one another in luminosity. In 1901 this had not yet been properly determined,
but Kapteyn divided the stars into two main groups and did a first, very preliminary investigation into how the laws of brightness and density depended
on this. He published this first attempt a year later in Publications of the Astro-