Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Road to Quasars   Although the extragalactic nature of 3C 48 and other quasi stellar radio
sources was discussed as early as 1960 by John Bolton and others, it was
rejected largely because of preconceived ideas about what appeared to be
unrealistically high radio and optical luminosities. Not until the 1962
occultations of the strong radio source 3C 273 at Parkes, which led Maarten
Schmidt to identify 3C 273 with an apparent stellar object at a redshift of
0.16, was the true nature understood. Successive radio and optical measurements
quickly led to the identification of other quasars with increasingly large
redshifts and the general, although for some decades not universal, acceptance
of quasars as the very luminous nuclei of galaxies. Curiously, 3C 273, which is
one of the strongest extragalactic sources in the sky, was first cataloged in
1959 and the magnitude 13 optical counterpart was observed at least as early as
1887. Since 1960, much fainter optical counterparts were being routinely
identified using accurate radio interferometer positions which were measured
primarily at the Caltech Owens Valley Radio Observatory. However, 3C 273 eluded
identification until the series of lunar occultation observations led by Cyril
Hazard. Although an accurate radio position had been obtained earlier with the
OVRO interferometer, inexplicably 3C 273 was initially misidentified with a
faint galaxy located about an arc minute away from the true quasar position.

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The categories of this paper are: cs
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The categories of this paper are: hep-lat
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The categories of this paper are: cond-mat
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The categories of this paper are: dg-ga
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The categories of this paper are: acc-phys
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The categories of this paper are: adap-org
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The categories of this paper are: math
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The categories of this paper are: nlin
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The categories of this paper are: hep-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-alg
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The categories of this paper are: eess
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The categories of this paper are: nucl-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: chao-dyn