9.2 First Visit, 1908
177
9.2 First Visit, 1908
Kapteyn’s first visit to Mount Wilson took place in 1908; the intention was
that it would coincide with the commissioning of the 60 in. telescope. Kapteyn
left the Netherlands on September 12th. However, the final construction of
the telescope turned out to be more difficult than expected, and he spent most
of his time at Mount Wilson waiting for the construction to be completed. He
lived at the observatory itself. Mount Wilson is a mountain just north and a
bit east of Pasadena, the town where the offices of the observatory are located.
The way up, the so-called Mount Wilson Toll Road, started in Altadena, 10 km
from Pasadena at an altitude of about 300 m above sea level. The road climbs
to the top of Mount Wilson, which is at 1740 m, over a distance of 16 km. The
trip was usually made with a wagon pulled by mules or horses, or sometimes on
horseback. At the time of Kapteyn’s first visit, the road had just been widened
to about 3 m, but it must have been quite an adventurous and demanding
undertaking (Fig. 9.3).
The program for which the 60 in. telescope would be used consisted of two
parts. The most important and urgent part for Kapteyn was the systematic
photographing of the fields in the Selected Areas in order to obtain counts of
stars to fainter brightnesses than previously possible. To sketch the perspective the following comparison. The catalogs of stars that existed until then,
such as the Bonner Durchmusterung in the north and the Cape Photographic
Durchmusterung in the south, covered the entire sky; the faintest stars in these
catalogs had a brightness of about magnitude 9.5, about 25 times fainter than
the naked eye can see. Across the whole sky that was about 800,000 stars. The
Carte du Ciel intended to catalog all stars to magnitude 11, so one hundred
times too faint for the human eye. But to study the distribution of stars in
space, it was necessary to go much further. The collaboration with Harvard
and Edward Pickering, which would produce photographic recordings of the
Selected Areas across the entire sky from two hemispheres, would lead to a catalog with all the stars up to about magnitude 14. But for the study he had in
mind, Kapteyn realized only too well that even this was not enough. That is
why the works with the 60 in. at Mount Wilson was so fundamental, because
the aim—at least for the part of the sky that can be seen from California—was
to complete the counts in the Selected Areas to magnitude 18 or 19, which is a
hundred thousand times fainter than the eye can see. For comparison: the Sun
would have an apparent magnitude of 18 at a distance of 4.3 kpc. And so the
Mount Wilson program was crucial to Kapteyn.
The second part of the program concerned the determination of radial
velocities of stars. This requires a large telescope, because the light is dispersed
177
9.2 First Visit, 1908
Kapteyn’s first visit to Mount Wilson took place in 1908; the intention was
that it would coincide with the commissioning of the 60 in. telescope. Kapteyn
left the Netherlands on September 12th. However, the final construction of
the telescope turned out to be more difficult than expected, and he spent most
of his time at Mount Wilson waiting for the construction to be completed. He
lived at the observatory itself. Mount Wilson is a mountain just north and a
bit east of Pasadena, the town where the offices of the observatory are located.
The way up, the so-called Mount Wilson Toll Road, started in Altadena, 10 km
from Pasadena at an altitude of about 300 m above sea level. The road climbs
to the top of Mount Wilson, which is at 1740 m, over a distance of 16 km. The
trip was usually made with a wagon pulled by mules or horses, or sometimes on
horseback. At the time of Kapteyn’s first visit, the road had just been widened
to about 3 m, but it must have been quite an adventurous and demanding
undertaking (Fig. 9.3).
The program for which the 60 in. telescope would be used consisted of two
parts. The most important and urgent part for Kapteyn was the systematic
photographing of the fields in the Selected Areas in order to obtain counts of
stars to fainter brightnesses than previously possible. To sketch the perspective the following comparison. The catalogs of stars that existed until then,
such as the Bonner Durchmusterung in the north and the Cape Photographic
Durchmusterung in the south, covered the entire sky; the faintest stars in these
catalogs had a brightness of about magnitude 9.5, about 25 times fainter than
the naked eye can see. Across the whole sky that was about 800,000 stars. The
Carte du Ciel intended to catalog all stars to magnitude 11, so one hundred
times too faint for the human eye. But to study the distribution of stars in
space, it was necessary to go much further. The collaboration with Harvard
and Edward Pickering, which would produce photographic recordings of the
Selected Areas across the entire sky from two hemispheres, would lead to a catalog with all the stars up to about magnitude 14. But for the study he had in
mind, Kapteyn realized only too well that even this was not enough. That is
why the works with the 60 in. at Mount Wilson was so fundamental, because
the aim—at least for the part of the sky that can be seen from California—was
to complete the counts in the Selected Areas to magnitude 18 or 19, which is a
hundred thousand times fainter than the eye can see. For comparison: the Sun
would have an apparent magnitude of 18 at a distance of 4.3 kpc. And so the
Mount Wilson program was crucial to Kapteyn.
The second part of the program concerned the determination of radial
velocities of stars. This requires a large telescope, because the light is dispersed