Sources

Where the sky comes from.

Positions and brightness

Yale Bright Star Catalogue, 5th Revised Edition (Hoffleit and Warren, 1991; VizieR V/50). Every star brighter than visual magnitude 5.5 is included. The position is J2000 right ascension and declination. The dot size is the Johnson V magnitude from that catalog.

Names

d3-celestial star names, compiled by Olaf Frohn in 2015. Each drawn star takes the name of the Hipparcos star within 0.05° of it. A proper name is preferred, then a Bayer designation such as β Ori, then a Flamsteed number, then the Hipparcos number. The twenty-one brightest proper names are set by hand so the label does not depend on that match.

Distances

Gaia Data Release 3 (ESA, 2022; VizieR I/355) when that parallax is usable: larger than 0.5 mas, at least 5 times its stated uncertainty, and with a renormalised unit-weight error under 1.4. Otherwise the distance is the 2007 re-reduction of Hipparcos (van Leeuwen; VizieR I/311), on the same 0.5 mas cutoff. Light-years are 3261.563777 divided by the parallax in milliarcseconds. Under 100 light-years the figure keeps one decimal. Beyond that it is rounded to the nearest light-year. A star with neither measurement is labeled distance unknown.

Constellations

d3-celestial constellation lines. The stick figures are the rank 1 and rank 2 lines. Copyright 2015 Olaf Frohn, BSD-3-Clause. The fainter rank 3 figures are left out.

Time

Each draw uses the clock at that moment. Greenwich mean sidereal time, in degrees, is approximated as 280.46061837 + 360.98564736629 × days since J2000.0. Adding the longitude, east positive, gives local sidereal time. Catalog positions stay at J2000. The sky does not keep turning while it sits on the screen. The next draw, after a drag or a new place, reads the clock again.