184
9 Mount Wilson
large part because they have intrinsically less luminosity. He also suggested that
absorption of starlight could be the cause of this. Kapteyn had commented on
this during his presentation in St. Louis, stating that this conclusion was far
from unique.
Kapteyn picked up his earlier work on the spatial distribution of the stars (see
Sect. 6.6). He suspected that one could explain some of the anomalies found by
the fact that you saw another part of the stellar distribution at greater distance,
namely the ones that are intrinsically brighter. But to prove that this was
indeed the cause, one had to have more information about the distribution of
intrinsic luminosities, the so-called ‘brightness curve’.The models that Kapteyn
was able to construct for this were not very accurate, but indicated that it
was likely that the results of Comstock and Pickering could be explained at
least partly by this brightness curve and partly by the absorption of starlight,
but that the latter was much less than these two astronomers had found. It
was clear that this was a problem and that the absence of absorption, the
assumption of a completely transparent space, was unlikely to be realistic.
For Kapteyn’s work, this presented a fundamental uncertainty and therefore a
major problem. Kapteyn also disagreed with the conclusions of Pickering and
Comstock, because models that assumed a high absorption of starlight resulted
in a distribution of stars in space with a large peak near the Sun. That the Sun
occupied such a special position was not acceptable to him, because the Sun
was after all supposed to be an average star among the stars. Since Copernicus
we are no longer the center of the Universe.
Before I discuss Kapteyn’s work in this area during his first years on Mount
Wilson, I will first discuss the current understanding. Figure 9.10, shows the
constellation Orion. 1 In this picture we see not only stars, but also more
extensive bright features. We see those particularly near the stars in the ‘belt’,
which are the three stars in a row in the middle, and at the end of the downward
pointing row below, which is called the ‘sword’. This latter object is the Orion
Nebula, which is shown in more detail in Fig. 9.11. There is also a large circular
structure in the picture, at least part of which is called Barnard’s Loop. The
latter is probably an expanding shell that lies further from us than the Orion
Nebula, and is left over from a supernova explosion at the end of a heavy star’s
life.
The Orion Nebula is an area of gas and dust. It is lit up by a group of
young stars, some of which are very heavy and hot. They produce a lot of
ultraviolet light, i.e. a lot of energy, and that radiation ionizes the hydrogen
(and other elements too, but hydrogen is the most common element), i.e.,
it releases the one electron that is around the hydrogen nucleus, a proton.
1 The name Orion is pronounced with the accent on the second syllable ‘ri’.
9 Mount Wilson
large part because they have intrinsically less luminosity. He also suggested that
absorption of starlight could be the cause of this. Kapteyn had commented on
this during his presentation in St. Louis, stating that this conclusion was far
from unique.
Kapteyn picked up his earlier work on the spatial distribution of the stars (see
Sect. 6.6). He suspected that one could explain some of the anomalies found by
the fact that you saw another part of the stellar distribution at greater distance,
namely the ones that are intrinsically brighter. But to prove that this was
indeed the cause, one had to have more information about the distribution of
intrinsic luminosities, the so-called ‘brightness curve’.The models that Kapteyn
was able to construct for this were not very accurate, but indicated that it
was likely that the results of Comstock and Pickering could be explained at
least partly by this brightness curve and partly by the absorption of starlight,
but that the latter was much less than these two astronomers had found. It
was clear that this was a problem and that the absence of absorption, the
assumption of a completely transparent space, was unlikely to be realistic.
For Kapteyn’s work, this presented a fundamental uncertainty and therefore a
major problem. Kapteyn also disagreed with the conclusions of Pickering and
Comstock, because models that assumed a high absorption of starlight resulted
in a distribution of stars in space with a large peak near the Sun. That the Sun
occupied such a special position was not acceptable to him, because the Sun
was after all supposed to be an average star among the stars. Since Copernicus
we are no longer the center of the Universe.
Before I discuss Kapteyn’s work in this area during his first years on Mount
Wilson, I will first discuss the current understanding. Figure 9.10, shows the
constellation Orion. 1 In this picture we see not only stars, but also more
extensive bright features. We see those particularly near the stars in the ‘belt’,
which are the three stars in a row in the middle, and at the end of the downward
pointing row below, which is called the ‘sword’. This latter object is the Orion
Nebula, which is shown in more detail in Fig. 9.11. There is also a large circular
structure in the picture, at least part of which is called Barnard’s Loop. The
latter is probably an expanding shell that lies further from us than the Orion
Nebula, and is left over from a supernova explosion at the end of a heavy star’s
life.
The Orion Nebula is an area of gas and dust. It is lit up by a group of
young stars, some of which are very heavy and hot. They produce a lot of
ultraviolet light, i.e. a lot of energy, and that radiation ionizes the hydrogen
(and other elements too, but hydrogen is the most common element), i.e.,
it releases the one electron that is around the hydrogen nucleus, a proton.
1 The name Orion is pronounced with the accent on the second syllable ‘ri’.