STARWATCH'S STAR AND OBJECT DATA
The data inside Starwatch, the live sky map for Garmin watches, shared under the
Creative Commons Attribution-ShareAlike 4.0 licence:
https://creativecommons.org/licenses/by-sa/4.0/

You may copy, share and adapt it, including commercially, as long as you credit the
sources below and share anything you make from it under the same licence.


SOURCES

- Stars and deep-sky objects: the HYG Database v4.1 and its deep-sky catalogue, by
  David Nash (https://www.astronexus.com/hyg), CC BY-SA 4.0.
- Corrections to 14 stars' spectral types, and the deep-sky objects' distances: Wikipedia
  (its pages on those stars, its lists of Messier and Caldwell objects and its pages on the
  others), CC BY-SA 4.0.
- Variable stars' brightness ranges: the General Catalogue of Variable Stars (N. N. Samus
  and others, Sternberg Astronomical Institute, Moscow), as listed in Wikipedia's List of
  variable stars, CC BY-SA 4.0.


WHAT WAS CHANGED

From HYG: the stars down to magnitude 7.0 only (15,598 of them); positions moved to the
epoch 2027.0 (proper motion, then precession); each star's B-V colour index turned into one
of four colours; named stars given a colour and type in words from their spectral type, with 14
spectral types corrected; distances rounded to about 0.3%. From the deep-sky catalogue: 150 objects
(all 110 Messier objects and 40 others), with some sizes, brightnesses and types corrected by
hand, and distances added from Wikipedia.


THE FILES

starwatch-stars.csv, one row per star:
  ra_deg, dec_deg   right ascension and declination in degrees, epoch 2027.0
  magnitude         apparent visual magnitude, to 0.1
  colour            white, blue, yellow or orange, from the B-V colour index
  constellation     the constellation the star is in, as HYG gives it
  name              its proper name, or Bayer or Flamsteed designation, where it has one
  type              colour and type in words, from the spectral type (named stars only)
  distance_ly       distance in light years, where known
  variable_range    for 22 well-known variable stars, the range of their brightness

starwatch-objects.csv, one row per deep-sky object:
  label, name       catalogue label (M31, NGC 869...) and common name
  type              galaxy, open cluster, globular cluster, nebula, planetary nebula,
                    supernova remnant, nebula and cluster, dark nebula, asterism,
                    star cloud or double star
  ra_deg, dec_deg   position in degrees, epoch 2027.0
  magnitude         apparent visual magnitude (none for the dark nebula)
  size_arcmin       its longest extent, in minutes of arc
  distance_ly       distance in light years, where known

json/: the same data exactly as the watch uses it, packed into whole numbers to save memory
(catalog.json, the stars in five brightness tiers cut into pieces as starsT_P.json, names.json
and objects.json). Starwatch's README explains the packing.
