The sky.
All around you.

Stars use the catalogue’s J2000 coordinates, with precession and nutation. Astronomy Engine calculates the Sun, Moon and planets for your observing location in topocentric coordinates. Altitudes are geometric, without atmospheric refraction. Without a landscape, the ground is a flat horizon at 0°. The photograph is fixed scenery from Stará Lesná, Slovakia; it does not reproduce terrain at your selected location.

The available period is 1900–2100. Stellar proper motion, parallax and aberration corrections are not modelled. Enriched Messier objects and NGC/IC targets use OpenNGC J2000 positions when available. Centre pointing and the equatorial grid use the equator and vernal point of the displayed date; star and deep-sky details show J2000 coordinates. The planner has its own refraction model, so small altitude differences near the horizon are possible.

Reality mode renders day, twilight, stars with soft brightness profiles and a generated Milky Way in the galactic frame. Its structure and dust lanes are illustrative, without photometric calibration. The Sun, Moon and proximity to the horizon affect the rendering. It is neither a weather forecast nor a full light-pollution simulation. Simple mode uses a schematic appearance; both modes share the same calculated positions.

Hipparcos supplies 5,044 bright stars. The Tycho-2 subset adds stars with mean J2000 positions and estimated V ≤ 11. The effective limit rises from 6 in wide views to 11 at high zoom, capped by your slider. Unique HIP/TYC cross-matches within 2 arcseconds are merged; ambiguous components remain separate. B−V colours and brightness are illustrative. Sky lighting and extinction near the horizon can hide stars.

In Reality mode the Moon uses the NASA/LRO photographic map, with calculated lighting, libration and orientation. Planets use reference illustrations, synthetic clouds for Venus and schematic rings for Saturn. Phases and angular diameters are calculated; clouds and surface details are not live images. Small bodies retain a minimum marker. “See close up” adjusts the zoom; turn off the ground to explore the theoretical position of a hidden object.

Messier photos are illustrative vignettes, mostly shown when zoomed in or when a target is selected. Their framing, size and orientation are not astrometrically calibrated. Eyepiece field ≈ apparent field ÷ magnification: instrument resolution, contrast and image inversion are not simulated. Actual observations depend on the sky, your instrument and your horizon.

The portal’s red night theme changes interface colours; the planetarium’s sun button changes sky lighting. Results describe a theoretical sky.

• d3-celestial, Olaf Frohn : snapshot dated 19 October 2026, 5,044 stars up to magnitude 6 and constellation lines and boundaries, in J2000 coordinates. Three-clause BSD licence. Astrometry and photometry: Hipparcos ESA 1997, retrieved directly from I/239; additional Gaia DR3 parameters, ESA/Gaia/DPAC · CC BY-NC 3.0 IGO. Names and designations: Kostjuk (2002), Smith (1996), Samus et al. and Gliese et al. indexes, referenced by d3-celestial. Translations from the sky culture tables are not included.
• Astronomy Engine, Don Cross, version 2.1.19: ephemerides, celestial frames and rotations. MIT licence.
• NGC and IC catalogues: OpenNGC · Mattia Verga, CC BY-SA 4.0. 8,373 NGC entries and 5,597 IC I and IC II entries. Locatable targets can be searched and selected in the sky. J2000 coordinates and symbolic markers.
• Messier objects: Steve Cimolino’s catalogue, NASA HEASARC and OpenNGC, Mattia Verga, coordinates adapted under CC BY-SA 4.0. Planner sources.
• Cities, approximate elevations and time zones: GeoNames, retained extract dated 18 October 2026, CC BY 4.0. Local time conversion: browser time zone database.
• Photographic landscape: Stará Lesná Meadows, Ľubomír Hambálek. Original PNG retained; projection and brightness adapted for display. CC BY 4.0 according to the original package. Landscape sources.
• Milky Way: Universum procedural rendering in the galactic frame supplied by Astronomy Engine. Lunar map: NASA/LRO; see lunar atlas sources and credits. NASA/LRO.

An independent creation for Universum · Steve Cimolino. Inspired by the open sky exploration offered by planetarium software; no affiliation with Stellarium. The sky is rendered using data retained on this site, without an external mapping service.