# Data sources and licences

## Stars: HYG database

`stars.json` comes from the HYG star database, version 3.8, by David Nash
(https://github.com/astronexus/HYG-Database, now at
https://codeberg.org/astronexus/hyg). It is licensed under Creative Commons
Attribution-ShareAlike 2.5 (https://creativecommons.org/licenses/by-sa/2.5/),
and `stars.json` is shared under the same licence.

What we changed: kept only the stars of magnitude 6.0 or brighter (the Sun
left out), turned right ascension from hours into degrees, rounded positions,
magnitudes and B-V colours to 2 decimals, wrote 0.6 where a star has no B-V
colour, sorted brightest first, and kept the constellation, distance (as
light years) and Bayer letter or Flamsteed number of every star, with the
proper names of named stars. Alpha Centauri A and B are set to
4.4 light years (HYG has 4.3).

## Constellations, Milky Way and deep-sky objects: d3-celestial

`constellations.json`, `milkyway.json` and the positions in `dsos.json`
come from d3-celestial by Olaf Frohn (https://github.com/ofrohn/d3-celestial).

What we changed: right ascension moved from -180..180 to 0..360 degrees and
rounded. Constellation lines and centres were merged into one file with
English names that a teacher would say, and the Latin spellings of Crux
(Crucis) and Corona Australis were corrected. The Milky Way outlines were rounded
to 0.1 degrees, and points closer than 0.5 degrees to the one before were
dropped. In `dsos.json`, the names, sizes, magnitudes, distances and
descriptions were written for this game; only the positions of most objects
come from d3-celestial.

Copyright (c) 2015, Olaf Frohn
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice,
   this list of conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice,
   this list of conditions and the following disclaimer in the documentation
   and/or other materials provided with the distribution.

3. Neither the name of the copyright holder nor the names of its contributors
   may be used to endorse or promote products derived from this software
   without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.

## Places

`places.json` was written for this game: town and city positions rounded to
0.01 degrees, with their IANA time zones. No licence applies.