These four catalogues come from the KStars free software
https://edu.kde.org/kstars/

The file format has been developed by the KStars team and is licensed as GPLv2
or above. The four files data and binary format are documented here:
https://api.kde.org/kstars/html/Stars.html

For more information about these files andd how to use them in Siril, see
https://free-astro.org/index.php?title=Siril:Star_Catalogues

The data in the catalogues comes from various sources: Hipparcos, Tycho-2 and
NOMAD.

Hipparcos catalogues
====================

There doesn't seem to be any license associated with this data, many software
use them and it seems to be public domain. The following notice should anyway
appear:

This application makes use of the Hipparcos and Tycho catalogues (ESA, 1997)
(http://sci.esa.int/hipparcos)


Tycho-2 Catalogue
===============

The Tycho-2 Catalogue is by Erik Høg et al. The copy of Tycho-2 used in
KStars was downloaded from the Astronomical Data Center, which was
hosted on http://adc.astro.umd.edu

The service is currently inaccessible, but at the time of download,
the content was licensed in the public domain:
http://adc.astro.umd.edu/adc/questions_feedback.html#policies1%22
said:

"All ADC data are public domain unless otherwise stated in the
"ReadMe" file. The data are for scientific use only and have no
commercial value."

The internet archive "WayBackMachine" still has the old page archived
and here is a link to the archived page on WayBackMachine showing the
public domain policy:
http://web.archive.org/web/20060908091808/http://adc.astro.umd.edu/adc/questions_feedback.html#policies1%22

See also the debian package copyright:
https://sources.debian.org/src/kstars-data-extra-tycho2/1.1r1-9.1/debian/copyright/

USNO NOMAD Catalogue
==================

The USNO NOMAD catalogue was compiled by the US Naval Observatory, and
access to the catalogue is (as of April 1, 2012) available through the
USNO website -- http://www.nofs.navy.mil/nomad/

The "Privacy and Security Notice" on USNO's website
(http://ad.usno.navy.mil/privacy.shtml) reads:

"All information presented on these pages is considered public domain
and may be distributed or copied unless otherwise specified. Use of
appropriate byline/photo/image credits is requested."

There is no explicit indication to the contrary on the NOMAD page.

NOMAD was obtained for use in KStars by Jason Harris, by contacting
Norbert Zacharias, who is designated as a contact point for questions
about the NOMAD catalogue on the USNO website.

