Sources & credits

The data and methods behind the star maps. Updated July 2026.

Constellation figures

The constellation stick figures (which stars are joined into each shape) are derived from the official IAU constellation figures by Sky & Telescope (Alan MacRobert, Roger Sinnott, Rick Fienberg), used under the Creative Commons Attribution (CC BY) licence. The line connections were recovered from the CC BY figure art and re-projected onto our own star catalog; the line joining Procyon and Gomeisa in Canis Minor is the common two-star asterism.

Star positions and brightness

Star coordinates and magnitudes are physical facts drawn from the Hipparcos catalogue, the Yale Bright Star Catalogue, and the HYG compilation. Factual astronomical measurements are not subject to copyright.

Constellation boundaries

The 88 constellations and their boundaries are the official scheme adopted by the International Astronomical Union (IAU) in 1928.

Planetary positions

Planetary and lunar positions are computed from the VSOP87 planetary theory (Bretagnon and Francou, Bureau des Longitudes) and standard algorithms from Jean Meeus, Astronomical Algorithms. These are published scientific methods; Undersky's implementation is entirely its own.

Places

Birthplace search runs entirely on your device against an offline extract of the GeoNames geographical database, used under the Creative Commons Attribution 4.0 licence. Nothing you type into that field leaves the phone.

Typefaces

Undersky is set in Fraunces and Mulish, both offered under the SIL Open Font License and bundled with the site so your visit is never tracked by a font host.

Contact

Questions: hello@undersky.app