Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Sunspot positions, areas, and group tilt angles for 1611-1631 from
  observations by Christoph Scheiner   Digital images of the observations printed in the books "Rosa Ursina sive
solis" and "Prodromus pro sole mobili" by Christoph Scheiner as well as the
drawings from Scheiner's letters to Marcus Welser are analysed in order to
obtain information on positions and sizes of sunspots that appeared before the
Maunder minimum. In most cases, the given orientation of the ecliptic is used
to set up the heliographic coordinate system for the drawings. Positions and
sizes are measured manually on the screen. Very early drawings have no
indication of their orientation. A rotational matching using common spots of
adjacent days is used in some cases, while in other cases, the assumption of
images being aligned with a zenith-horizon coordinate system appeared to be the
most probable. In total, 8167 sunspots were measured. A distribution of sunspot
latitudes versus time (butterfly diagram) is obtained for Scheiner's
observations. The observations of 1611 are very inaccurate, the drawings of
1612 have at least an indication of their orientation, while the remaining part
of the spot positions from 1618-1631 have good to very good accuracy. We also
computed 697 tilt angles of apparently bipolar sunspot groups observed in the
period 1618-1631. We find that the average tilt angle of nearly 4 degrees is
not significantly different from 20th-century values.

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The categories of this paper are: physics
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The categories of this paper are: chao-dyn
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The categories of this paper are: atom-ph
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The categories of this paper are: econ
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The categories of this paper are: mtrl-th
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The categories of this paper are: gr-qc
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The categories of this paper are: eess
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The categories of this paper are: acc-phys
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The categories of this paper are: chem-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: bayes-an
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-th
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The categories of this paper are: math
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The categories of this paper are: cs
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The categories of this paper are: q-fin