Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Lessons from the Milky Way: the Kapteyn Universe   Jacobus Cornelius Kapteyn (1851-1922) presented a model for the distribution
of stars in space together with a dynamical interpretation in terms of an
equilibrium between the gravitational field of the stars and their random
motion and rotation. In the vertical direction Kapteyn's results are
substantially correct. Usually the Kapteyn Universe is described as being
flawed due to neglect of interstellar absorption. Kapteyn was led to adopt this
on the basis of widely accepted evidence by Shapley on an absence of reddening
of stars in globular clusters. But another, equally important misconception was
Kapteyn's interpretation of the two Star Streams as manifestations of two
groups of stars rotating around a center in opposite directions. This was
supported by the observation of very different mixes in stellar types in the
two streams. Had Kapteyn adopted the absorption as he himself had determined it
he would not have been able to arrive at a consistent picture.

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The categories of this paper are: hep-ex
37
The categories of this paper are: supr-con
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
33
The categories of this paper are: plasm-ph
2
The categories of this paper are: math
25
The categories of this paper are: patt-sol
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The categories of this paper are: eess
24
The categories of this paper are: dg-ga
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The categories of this paper are: hep-ph
35
The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-th
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The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
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The categories of this paper are: stat
27
The categories of this paper are: comp-gas