constellations.json is derived from the "western" sky culture figures of Stellarium
(constellationship.fab, https://stellarium.org), which are distributed under the
GNU General Public License, version 2 or later. This file is offered under the same licence.
It lists, for each constellation, pairs of Hipparcos catalogue numbers that are joined by a line.

stars.json is derived from the Hipparcos Catalogue (ESA, 1997, The Hipparcos and Tycho
Catalogues, ESA SP-1200): stars to magnitude 6.0, positions rounded to 0.01 degree.