Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Lyman-{\alpha} Sky Background as Observed by New Horizons   Recent observations of interplanetary medium (IPM) atomic hydrogen
Lyman-{\alpha} (Ly{\alpha}) emission in the outer solar system, made with the
Alice ultraviolet spectrograph on New Horizons (NH), are presented. The
observations include regularly spaced great-circle scans of the sky and pointed
observations near the downstream and upstream flow directions of interstellar H
atoms. The NH Alice data agree very well with the much earlier Voyager UVS
results, after these are reduced by a factor of 2.4 in brightness, in
accordance with recent re-analyses. In particular, the falloff of IPM
Ly{\alpha} brightness in the upstream-looking direction as a function of
spacecraft distance from the Sun is well-matched by an expected 1/r dependence,
but with an added constant brightness of ~40 Rayleighs. This additional
brightness is a possible signature of the hydrogen wall at the heliopause or of
a more distant background. Ongoing observations are planned at a cadence of
roughly twice per year.

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The categories of this paper are: nucl-th
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The categories of this paper are: hep-lat
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The categories of this paper are: acc-phys
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The categories of this paper are: quant-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: cond-mat
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The categories of this paper are: q-fin
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The categories of this paper are: dg-ga
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The categories of this paper are: math
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The categories of this paper are: atom-ph
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The categories of this paper are: cs
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The categories of this paper are: supr-con
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The categories of this paper are: eess
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The categories of this paper are: adap-org
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The categories of this paper are: bayes-an
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The categories of this paper are: funct-an