README.md

Stellata

Explore the universe.

A physically accurate 3D model of our local corner of the universe at every scale astronomy has measured it. Experience what it would actually look like to be there: from individual stars and their planets, through the local interstellar medium, out to the structure of the galactic disc, and beyond into the intergalactic void.

Every object in Stellata comes from a published observational catalogue and direct measurement: if we've measured it, it's here. Theoretical predictions and conjectured structures are excluded. The model's scope is bounded by what has been observed, currently enclosing a volume up to 6.5 million light years from our solar system.

Try it at https://stellata.xyz.

Highlights

• Everything is rendered live, from where you are. Over 330,000 real stars and objects — planets and moons, multiple-star systems, the volumetric Milky Way, the Local Group dwarf galaxies, and the 3D dust between them continually re-render against the current camera position each frame. Fly halfway to Sirius and the sky changes: parallax, reddening, and occlusion are all real, not fabricated.

• Close-up stars resolve as physical objects. Approach a star and it stops being a dot: its disc grows to its actual radius (from catalogue absolute magnitude + spectral class via Stefan–Boltzmann) and occludes whatever is behind it. Supergiants like Betelgeuse fill half the viewport; white dwarfs render as crisp small points.

• Interstellar dust dims and reddens stars correctly. The vertex shader raymarches the Edenhofer 2023 3D dust map from camera to star at run time, so stars behind dense ISM look fainter and redder, exactly as you would see them.

• Molecular clouds have real shape. The local star-forming clouds (Taurus, Orion, Ophiuchus and their neighbours) render as dust silhouettes traced directly from the Edenhofer field, and dim the diffuse background behind them.

• Variable stars pulsate. ~3,700 stars cross-matched with GCVS pulse at their true catalogue period on the model clock — brightness, disc radius, and colour all swing together. Open the time scrubber (T) to accelerate time and watch a Cepheid or Mira run through a cycle.

• The solar system at live planetary positions. Around Sol, the eight planets and Pluto render at their current heliocentric positions (JPL Standish ephemerides, sub-arcminute accurate 3000 BC – 3000 AD), with their major moons, atmospheres, and axial rotation, inside the asymmetric heliopause shell measured by Voyager and IBEX. A small clock in the corner shows the UTC time the positions correspond to.

• The Milky Way is volumetric, not a skybox. A bounded raymarch through galactic-scale density meshes produces the surface- brightness band. Fly past the galactic centre and it reorients with proper parallax. Analytical mid-plane dust means the dark lane reads correctly.

• A paper-chart mode for when you want to read the sky like a star atlas. A second visual mode is inspired by Sky Atlas 2000.0: flat hard-edged discs sized by apparent magnitude, full Bayer/Flamsteed labels, constellation names, double-star wings, variable-star rings.

• Navigate, observe, warp. Orbit any star (navigate), or land on it and look at the sky from its location (observe). Pick a second star to measure the distance, then warp: an animated camera flight between the two stars with full physical scaling.

• Shareable views. All settings plus camera pose pack into the current URL, so any view can be bookmarked and shared.

Grounded in published science

Everything you see is calibrated against the source data. Star sizes come from absolute magnitudes via Stefan–Boltzmann; halo softness tracks MK luminosity class; double and multiple stars come from the Washington Double Star Catalog and ORB6, with Gaia DR3 NSS and the Pulkovo Multiple Star Catalog for orbits; dwarf galaxies in the Local Group come from Pace 2024's Local Volume Database with hand-curated structural detail for the LMC, SMC, M31, M33, and Sagittarius dSph from the primary literature.

The full record of sources, formulas, and deliberate modelling simplifications lives in SCIENCE.md. Read for citations, DOIs, and what is and isn't observationally grounded.

Things to try

Stellata rewards exploration more than reading. A short curated list of viewpoints and objects, each chosen because it exercises something the renderer does that doesn't quite show up in a screenshot.

See the giants as physical objects

Approach these slowly. The discs grow to the star's real radius computed from its catalogued absolute magnitude and spectral class, so they fill the viewport long before you'd expect.

• Betelgeuse (α Orionis) — the canonical red supergiant. M2 Ia at 152 pc; the disc resolves to a large fraction of the viewport at close range.
• Antares (α Scorpii) — the other canonical red supergiant. M1.5 Iab at 170 pc. Visibly redder than Betelgeuse.
• Rigel (β Orionis) — blue supergiant in the same constellation as Betelgeuse. B8 Ia at 265 pc, intrinsically brighter than Betelgeuse — but hotter, so Stefan–Boltzmann gives it a smaller physical radius. The Rigel / Betelgeuse pair makes the L = R²T⁴ trade-off visible.
• Deneb (α Cygni) — A2 Ia supergiant at 433 pc, in Cygnus. Renders as a notably bright white-blue disc.

Watch variables pulse

Variables pulse at their true GCVS period on the model clock. Open the time scrubber (press T) to accelerate time, then focus on one and watch it swing in brightness, size, and colour:

• δ Cephei — the namesake Cepheid.
• η Aquilae — another bright classical Cepheid.
• Mira (o Ceti) — the long-period prototype; the amplitude is dramatic.
• Betelgeuse — a slow, low-amplitude pulse, visible as both a brightness swing and a physical disc-radius change if you're focused close in.

Fly out and watch the constellations break

The constellation lines come from Earth's viewpoint. Move just a few tens of parsecs and the figures visibly deform — this is the moment the model stops being a planetarium and starts being a 3D map.

• Orion — Betelgeuse (~152 pc) and Rigel (~265 pc) are at very different distances; flying through Orion stretches the figure asymmetrically.
• Big Dipper / Ursa Major — most members belong to the Ursa Major moving group, but Dubhe (α UMa) and Alkaid (η UMa) don't. The asterism breaks lopsidedly as you back away.
• Cygnus — Deneb is at ~433 pc, the rest of the Northern Cross much closer. Backing the camera off tilts the cross dramatically.

Visual doubles, in chart mode

Switch to chart mode while observing from a focused star to see the double-star wings glyph. The model flags ~13,000 doubles via the Hipparcos CCDM cross-match.

• Mizar + Alcor (ζ + 80 UMa) — the classic naked-eye double. Both stars are in the catalogue at distinct positions, so they render as two separate discs; Mizar additionally carries the binary wings glyph in chart mode.
• Albireo (β¹ + β² Cygni) — Earth's favourite colour-contrast pair, gold and blue. Stellata's 3D positions reveal it as an optical double rather than a true binary: β¹ at 111 pc, β² at 122 pc, ~35 light-years apart along the line of sight — far too distant to be gravitationally bound. The colour contrast is real; the pairing is a chance alignment. (This matches the modern post-Gaia consensus, which retired Albireo from binary- catalogue status around 2018.)
• ε Lyrae — the wide "double double" pair. ε¹ and ε² Lyr are catalogued separately and render as a visible naked-eye pair; each carries the binary wings glyph in chart mode (each is itself a close binary that Hipparcos resolves).

Beyond the heliopause

The default first-load view parks you 5 AU from Sol facing the galactic centre — a deliberate "you are here, that's our system" anchor. From there:

• From Pluto, looking inward. The Sun is just one bright star among many; the heliopause shell sits overhead.
• Cross the heliopause at the upwind apex (~122 AU) and look back. The model's asymmetry — ~115 AU at the flanks, ~200 AU into the heliotail — reads from outside the bubble.

Watch the dust shape the sky

Set the magnitude limit to "All" (showing all ~330,000 stars) and pull the camera out to ~3 kpc from Sol, then orbit around. The Edenhofer 2023 3D dust grid is real volumetric structure, not an analytical shell — as you move, extinction patterns paint themselves across the stellar density as filaments and clumps that follow the actual local ISM. Stars behind dense lanes dim and redden; stars in clear windows shine through. Combined with the live per-camera apparent-magnitude recomputation (further = dimmer), the effect reads more like a map of the local ISM than a star-chart background.

Galactic-scale views

The Milky Way is volumetric, not a skybox. These viewpoints prove it:

• Park 8 kpc above the galactic centre and look down. The disc and bulge render as illuminated 3D structures; their orientation responds to camera motion.
• Stand on a star a few kpc out and look around. The MW band wraps continuously, with parallax that wouldn't be possible from a flat backdrop.
• Fly toward the galactic centre. As you cross into the bulge, the surface brightness of the volumetric band ramps. The dark dust lane along the midplane (a Drimmel–Spergel analytical profile baked into the band's own raymarch) reads correctly as you orient along the disc plane.

Local Group destinations

For ambitious distances. The Local Group layer renders LineLoop wireframes for confirmed-galaxy members out to 2 Mpc.

• Sagittarius dSph (~26 kpc) — our closest companion dwarf, currently being tidally torn apart by the MW. The wireframe shows the elongated structural axis that captures.
• LMC / SMC (~50 / 63 kpc) — the Magellanic Clouds render with hand-curated structure (LMC: inclined disc at i = 32°; SMC: triaxial along line of sight) rather than the default oblate ellipsoid.
• M31 (Andromeda, 776 kpc) and M33 (Triangulum, 840 kpc) — the two major spirals beyond the MW; M31's inclined disc (i = 77°) is visible.

Browser support

• WebGL2 required (any browser from 2018 onward — Safari 15+, Chrome 56+, Firefox 51+).
• Loads and renders on any device, but the user interface for mobile devices / small viewports is currently pending a future update.

Gestures

The two-finger rotate gesture (roll the view around the screen centre) is available on:

• Mobile / touch — iOS Safari, Android Chrome, any browser that exposes multi-touch touchmove events.
• Desktop Safari — via the macOS trackpad two-finger rotate gesture, detected through Safari's non-standard gesturechange event.

Chrome and Firefox on desktop do not expose a rotate gesture (they consume two-finger trackpad input for scroll/pinch only), so roll is unavailable in those browsers by design. All other navigation (orbit, zoom, pan) works the same everywhere.

Known limitations

• Only ~3,700 variables pulse — those successfully cross-matched between AT-HYG (via HIP or HD) and GCVS. Variables without a HIP/HD cross-reference, or whose GCVS entry lacks a parseable period, render as non-variable.
• Emission and reflection nebulae are not modelled yet. The local molecular clouds (Zucker 2020/2021) now render as traced dust silhouettes, but catalogued H II regions, planetary nebulae, and reflection nebulae are not yet drawn as discrete objects.

Sponsorship

Stellata is built and maintained in my spare time. If it's useful to you and you'd like to support continued development, sponsorship through GitHub Sponsors is warmly welcomed.

Contributing

The issue tracker is open. Bug reports and enhancement suggestions are welcome. External pull requests are not currently accepted; see .github/CONTRIBUTING.md for the full rationale and how to write a useful bug report or feature request.

Licence

The code in this repository is licensed under AGPL-3.0-only. See LICENSE.

Data sources retain their own licences:

• AT-HYG v3.3 (stellar catalogue) — David Nash, Codeberg, CC-BY-SA-4.0. The generated catalog.bin and search-index.json are derivatives and carry the same licence.
• Gaia DR3 (astrometry, astrophysical parameters, NSS orbits) — ESA / Gaia / DPAC, Gaia archive, CC-BY-4.0 (Gaia data-release policy).
• Bailer-Jones et al. 2021 (Gaia DR3 geometric distances) — via CDS/VizieR; cite the paper (10.3847/1538-3881/abd806).
• SIMBAD (cross-identifications + validation sample) — CDS Strasbourg, simbad.cds.unistra.fr; publicly accessible per CDS policy (academic / non-commercial), cite Wenger et al. 2000.
• GCVS 5.1 (variable stars) — Samus et al at the Sternberg Astronomical Institute, http://www.sai.msu.su/gcvs/gcvs/. Free for research and educational use with attribution.
• Hipparcos Main Catalogue + CCDM (ESA SP-1200, 1997; Dommanget & Nys 1994) — public domain via CDS.
• Washington Double Star Catalog + ORB6 (double-star geometry and visual orbits) — U.S. Naval Observatory, astro.gsu.edu/wds; public domain (U.S. Government work).
• Multiple Star Catalog (hierarchical multiple-star orbits) — Tokovinin 2018, via CDS/VizieR (J/ApJS/235/6); standard academic use, cite the paper.
• Stellarium modern sky culture (constellation stick figures) — Stellarium, MIT-licensed (line data; illustrations not used).
• Edenhofer et al. 2023 3D dust map — Zenodo, CC-BY-4.0. The resampled voxel grid in data/dust/ is a derivative and carries the same licence.
• Pace 2024 Local Volume Database (dwarf galaxies) — arXiv:2411.07424, CC0. The dwarf_all snapshot at data/local-group/lvdb-snapshot.csv is a frozen copy of the upstream table.
• Zucker 2020 + 2021 (molecular cloud distances and bounding boxes) — 10.3847/1538-4357/ab9d24 and 10.3847/1538-4357/ac1f96.

See SCIENCE.md and docs/science-local-group.md for citation details and the peer-reviewed papers underpinning hand-curated Local Group overrides (LMC, SMC, M31, M33, Sgr dSph, M 32, NGC 205).