Outer Horizon
Stellar map · The known universe, to scale
Outer Horizon is a map you zoom out of. It starts at home and lets you travel outward, level by level: past the planets, to the nearest stars, through the Milky Way, into the Local Group and on to the edge of what we can observe. Every distance and size is real. Nothing is shown that has not been catalogued, and beyond the horizon the map is black.
The point is proportion. Neptune is far. The nearest star is thousands of times further. The next galaxy is almost a million times further than that. Zooming through those steps with your own fingers makes the numbers mean something.
How to read the map
- Names appear when they belong to the level you are at. Zoom out and planets give way to stars, stars to galaxies.
- The scale bar in the corner tells you how wide the view is, from kilometres to billions of light-years.
- The round overview shows where you are: rings are distances from the Sun on a logarithmic scale, the dot is you, the circle around it is your view. Tap a ring to jump there.
- "Next:" tells you what comes after the last thing you saw, and how many times further it is.
- Models are marked. We cannot see the Milky Way from outside, and the Oort Cloud has never been imaged. Where a shape is a model or an illustration, the info card says so. Its position is still real.
- Black means unknown. No decorative stars, no invented background. Empty space is empty because that is what we know.
Controls
| Action | Touch | Mouse / trackpad |
|---|---|---|
| Move | One finger | Drag |
| Zoom towards a point | Pinch | Scroll or pinch |
| Rotate | Two fingers | Right-drag or Shift + drag |
| Info | Tap | Click |
| Fly in | Double-tap | Double-click |
| Home | House button | H |
| Search | Magnifier | / |
"Center & lock" in the info card keeps an object centred; dragging then orbits it. Zooming is limited to about one order of magnitude per second, so a flick never skips a level.
Scale and accuracy
Positions are computed in astronomical units at full double precision and rendered relative to the camera, which keeps the view steady from the Moon's orbit to the cosmic horizon. Planets, dwarf planets and comets move on their real orbits from published orbital elements, correct to the day for the planets and approximate for the small bodies. Stars and galaxies sit at their catalogued coordinates and distances. Distances in the catalogue are rounded; distances to far galaxies and clusters carry the uncertainty of the literature they come from, often 5–10%.
Bodies are never shown closer than a quarter of the screen. This is a map of where things are, not of what their surfaces look like.
Data sources
Every object in the catalogue names its source. The providers ask to be credited as follows.
| Source | Used for |
|---|---|
| SIMBAD | Stars, star clusters and nebulae: coordinates, distances, spectral types and temperatures |
| NED | Galaxies, galaxy clusters and large-scale structures: coordinates and distances |
| JPL Solar System Dynamics | Planetary mean orbital elements (J2000) and the Small-Body Database for dwarf planets and comets |
| NASA | Planetary and satellite fact sheets: radii, orbital periods, moon distances; Voyager and New Horizons positions |
| Event Horizon Telescope | Sagittarius A* |
| Gaia DR3 | The stellar background: the brightest stars within about 1,000 light-years, with distances from parallax and colours from temperature |
| 2MRS | The galaxy background: the 2MASS Redshift Survey, about 45,000 galaxies with distances from redshift |
| Literature | Superclusters, walls and voids, where no single catalogue entry exists |
This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France (Wenger et al. 2000, A&AS 143, 9).
This research has made use of the NASA/IPAC Extragalactic Database (NED), which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology.
Orbital elements and small-body data courtesy of the JPL Solar System Dynamics group, NASA/JPL-Caltech.
This work has made use of data from the European Space Agency (ESA) mission Gaia (cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC, cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement.
This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. 2MRS: Huchra et al. 2012, ApJS 199, 26, via the VizieR catalogue access tool, CDS, Strasbourg, France.
Star colours are computed from each star's effective temperature as black-body radiation. The Milky Way model follows the mapped bar and spiral arms with the Sun 26,700 light-years from the centre; the shapes of other galaxies, clusters and nebulae are illustrations placed at their real positions.
Adding to the catalogue
The catalogue is a plain data file with one entry per object: a name, a type, a position and a source. New discoveries are added as data, without touching the map itself.
Privacy
The map runs entirely in your browser. It stores your language and home-view choice on your device and nothing else. There is no tracking. If you open a Wikipedia summary from an info card, your browser fetches it directly from Wikimedia's servers, which then see your request like any visit to Wikipedia.