7.6 Plan of Selected Areas
147
light is refracted more than red light, so that with a simple lens the image is not
formed in exactly the same place in different colors. This is called chromatic
aberration. This can be solved with achromatic lenses, which consist of several
parts stuck together, that are made of various materials with different refractive
properties. With mirrors there is spherical aberration because, with a spherical
surface of the mirror, the image is formed in a different place when it is reflected
at the edge than when it is reflected in the center. This can be solved by making
the surface parabolic, but that is difficult and also makes the field of view, the
area over which good stellar images are formed, smaller.
The Yerkes telescope had a primary lens with a diameter of 102 cm (40 in.).
George Hale was originally a solar astronomer, but in order to understand the
Sun, he felt he had to study other stars as well. In 1903 he was in California,
where he visited among others Mount Wilson near Pasadena as a potential
location for an observatory. Edward Pickering had also had had an eye on that
spot earlier. George Hale secured the support of the Carnegie Institution of
Washington (presently ‘of Science’), founded in 1902 by steel magnate and
philanthropist Andrew Carnegie (1835–1919) to promote science. On the
land that George Hale was able to purchase with the funds the Institution
provided, he initially installed a few solar telescopes from Yerkes and then had
two enormous solar towers built; since a long focal length is required for the
this, those telescopes were built vertically, with the focal point below ground,
where it is cooler. But George Hale also wanted to do night astronomy on
Mount Wilson; he made plans for a telescope with a mirror diameter of no
less than 60 in. (152 cm). That would then be the largest in the world. The
conditions for astronomical observations on Mount Wilson were superior to
those at other places, due to the usually clear weather in Southern California
and the calm atmosphere at an altitude of 1740 ms. George Hale, as we will see,
proposed to use his ‘giant telescope’ of 60 in. aperture for the Plan of Selected
Areas of Kapteyn.
147
light is refracted more than red light, so that with a simple lens the image is not
formed in exactly the same place in different colors. This is called chromatic
aberration. This can be solved with achromatic lenses, which consist of several
parts stuck together, that are made of various materials with different refractive
properties. With mirrors there is spherical aberration because, with a spherical
surface of the mirror, the image is formed in a different place when it is reflected
at the edge than when it is reflected in the center. This can be solved by making
the surface parabolic, but that is difficult and also makes the field of view, the
area over which good stellar images are formed, smaller.
The Yerkes telescope had a primary lens with a diameter of 102 cm (40 in.).
George Hale was originally a solar astronomer, but in order to understand the
Sun, he felt he had to study other stars as well. In 1903 he was in California,
where he visited among others Mount Wilson near Pasadena as a potential
location for an observatory. Edward Pickering had also had had an eye on that
spot earlier. George Hale secured the support of the Carnegie Institution of
Washington (presently ‘of Science’), founded in 1902 by steel magnate and
philanthropist Andrew Carnegie (1835–1919) to promote science. On the
land that George Hale was able to purchase with the funds the Institution
provided, he initially installed a few solar telescopes from Yerkes and then had
two enormous solar towers built; since a long focal length is required for the
this, those telescopes were built vertically, with the focal point below ground,
where it is cooler. But George Hale also wanted to do night astronomy on
Mount Wilson; he made plans for a telescope with a mirror diameter of no
less than 60 in. (152 cm). That would then be the largest in the world. The
conditions for astronomical observations on Mount Wilson were superior to
those at other places, due to the usually clear weather in Southern California
and the calm atmosphere at an altitude of 1740 ms. George Hale, as we will see,
proposed to use his ‘giant telescope’ of 60 in. aperture for the Plan of Selected
Areas of Kapteyn.