The Journal · July 30, 2026

Data sources and credits

SkyChart stands on decades of work by astronomers, cartographers, illustrators and open-source developers. Every catalogue, texture and illustration in the app is listed below with its source and licence. Where a licence requires attribution, this page is that attribution.

Stars

HYG Database v4.1 — the 41,600 stars shown, down to magnitude 8. David Nash's compilation of the Hipparcos (ESA), Yale Bright Star and Gliese catalogues. Licence CC BY-SA 4.0.
IAU Catalog of Star Names — the 420 proper names, as approved by the IAU Working Group on Star Names. Public data.
NASA Exoplanet Archive — the 443 stars flagged as hosting confirmed exoplanets. Operated by Caltech under contract with NASA. Public domain.

Constellations

Line figures — the Sky & Telescope set, distributed through the Stellarium sky cultures project under CC BY-SA 4.0. These are the figures found in most star atlases.
Boundaries — the official IAU boundaries, digitised by Olaf Frohn for d3-celestial (BSD 3-clause), after Eugène Delporte's 1930 delimitation adopted by the IAU.
Illustrations — artwork by Johan Meuris, distributed with Stellarium under the Free Art License.

Sky cultures

The alternative sky cultures are contributed work from the Stellarium project. They are not decorative reinterpretations: each one documents how a specific people reads the same sky.

Inuit — contributed by Karrie Berglund (Digitalis Education Solutions), after The Arctic Sky by John MacDonald. Data GNU GPL v2, illustrations Free Art License.
Boorong — the Boorong people of Lake Tyrrell, Australia. Contributed by John Morieson and Alex Cherney. Data and illustrations CC BY-SA.
Romanian — contributed by Mircea Lite and the Baia Mare Planetarium (Traditional Romanian Constellations, 2012-2013), after Romanian peasants beliefs in stars and sky by Ion Ottescu. Texts, lines and illustrations CC BY-SA.

Deep sky

OpenNGC — the 1,735 deep-sky objects, including the complete Messier and Caldwell catalogues. Mattia Verga's database, licence CC BY-SA 4.0.
Nebula and cluster imagery — photographic textures distributed with Stellarium (GPL v2+). Individual photographers are credited per object in the app.
Meteor showers — activity periods, peak dates and zenithal hourly rates from the International Meteor Organization.

Solar system

Ephemerides — computed with astronomy-engine by Don Cross (MIT), which implements VSOP87 and other standard theories. Nothing is read from a table: every position is calculated for your exact time and place.
Orbital elements for Ceres and Vesta — JPL Small-Body Database, NASA/JPL-Caltech.
Planetary textures — distributed with Stellarium (GPL v2+), largely derived from NASA and USGS imagery in the public domain.

Satellites

Orbital elements — two-line element sets from CelesTrak, refreshed several times a day.
Propagation — SGP4 via satellite.js (MIT).

Observing conditions

Light pollution — the Bortle class and sky brightness estimate come from David J. Lorenz's Light Pollution Atlas 2024, derived from VIIRS/DNB satellite observations.
Weather — forecasts from Open-Meteo (CC BY 4.0).
Maps — Leaflet (BSD 2-clause), tiles from OpenStreetMap contributors and CARTO, satellite imagery from Esri, Maxar and Earthstar Geographics.

Typography

Playfair Display, Montserrat, Spectral and IBM Plex Mono, all under open licences (SIL Open Font License and Apache 2.0).

A note on accuracy

We compute rather than approximate, and we say so when we cannot. Positions are accurate to the arcminute or better for everything the naked eye and binoculars can reach. Two limits we state openly: the Bortle class is an estimate derived from satellite measurements, not a reading taken where you stand; and the positions of Ceres and Vesta come from Keplerian elements that ignore planetary perturbations, so they hold to well under an arcminute over about eighteen months and drift beyond that.

If you spot an error, or a credit we have missed, write to us and we will fix it.