Data Sources

Stars
Big Sky Catalog - compilation of Hipparcos, Tycho-1, Tycho-2 in Epoch J2000

Constellation Lines
Stellarium (via Sky & Telescope)

Constellation Borders
IAU Constellation page
Catalogue of Constellation Boundary Data; Davenhall A.C., Leggett S.K. (1989) VizieR VI/49 (via d3-celestial)

Deep Sky Objects (DSOs)
OpenNGC - compilation of the New General Catalogue (NGC) and Index Catalogue (IC)

Moon & Planet Sizes
NASA - Solar System Sizes
NASA - Moon Facts

Milky Way Outline
Created by Steve Berardi with QGIS + GDAL from NASA's Deep Star Maps