Explanation
Data and licences
Where each part of the data comes from, what each licence lets an MIT package pass on, and what is deliberately left out.
The code is MIT. The data is in tiers, and a tier is in the package only if its licence lets an MIT package pass it on. NOTICE.md in the repository names every source, the sentence relied on and the day it was read; this page is the short version.
| Part | Source | Footing |
|---|---|---|
| The 5,080 stars | The Yale Bright Star Catalogue (Hoffleit and Warren 1991), from NASA HEASARC | The catalogue calls itself public domain and asks for credit, which the notice gives. There is no formal licence text, so the footing is informal. |
| Star names | The IAU Working Group on Star Names | A list of facts. |
| The 88 constellations, in English and Japanese | The IAU list; the National Astronomical Observatory of Japan | Names are facts, typed from published lists. No Wikipedia text. |
| Constellation boundaries | N. G. Roman (1987) from E. Delporte (1930), VizieR VI/42 | No licence stated; kept with credit and removed on request. |
| Constellation lines | Ours | Decided from the star data; no figure is copied from a book, atlas or program. |
| Messier, NGC and IC objects | Wikidata (CC0), checked against NASA/IPAC NED | CC0; positions corrected from NED where they disagree. |
| The Milky Way's brightness | SAO star counts (NASA HEASARC), the IRAS 100 micron dust map and COBE DIRBE (NASA), and a bulge of our own figures | The SAO catalogue states no licence: used with credit and removed on request. The two infrared maps are NASA mission data (public domain). No picture of the sky is read or traced. |
| Projections, sidereal time, refraction | Snyder's Map Projections and Meeus's Astronomical Algorithms | Formulas; no book text or library code. |
Left out on purpose
- ESA's Hipparcos, Tycho and Gaia are CC BY-NC 3.0 IGO: non-commercial, which an MIT package cannot pass on.
- HYG, AT-HYG and OpenNGC are CC BY-SA, which would put share-alike on this package's data.
- Stellarium's sky-culture files are GPL, and d3-celestial's data has no stated licence. The constellation figures here are our own for that reason.
Stars fainter than 6.0 are not in the package. When a clear-licence catalogue is found they will be a tier of their own.
How a number is checked
A test holds each count and each famous value: 15, 50, 174, 518, 1,630 and 5,080 stars to magnitudes 1 to 6; every bright star lies in the constellation the catalogue names, by the boundaries; every line's stars lie in its own constellation; the Messier, NGC and IC positions are NED's wherever Wikidata's was more than a minute of arc away. A failing test is a reason not to publish.