SkyRef computes every position in your browser from published catalogues and ephemerides. Nothing here is guessed at, and where a number is an estimate it says so.
All 9,096 stars SkyRef draws, with J2000 coordinates, visual magnitudes and B−V colour indices. Hoffleit & Warren, Astronomical Data Center.
VSOP87 and JPL-derived ephemerides, evaluated locally. Also supplies rise, set and transit times, twilight boundaries and lunar phase.
IAU constellation line figures and label positions, by Olaf Frohn. 89 figures, 150 line segments.
City search. Results are proxied and cached by SkyRef so the service is not queried repeatedly for the same place. © OpenStreetMap contributors.
There is no openly licensed dataset of night-sky brightness that permits commercial use — the standard reference, Falchi's World Atlas of Artificial Night Sky Brightness, is CC-BY-NC. SkyRef therefore treats Bortle class as something you set yourself, and any default it offers is labelled an estimate. It will not show you a precise-looking number it cannot stand behind.