XEphem sky viewer, reborn in the browser

Public quest. Recreate the Sky View of XEphem — the Motif/X11 ephemeris that has looked like 1993 since 1993 — as a browser app. The astronomy is a solved problem; the UI is the project. Rohan has never run the app, only seen screenshots, and loves exactly that: the 90s Unix aesthetic, on purpose.

The program being honored

The Sky View is the window that matters: an interactive star chart — zoom, pan, coordinate grids, constellation figures, catalog overlays, marks, DSS image downloads. (Mouse-wheel zoom only arrived in 4.2.0, Feb 2024 — the interface stayed period-correct for three decades, which is the whole charm.)

What to build (cheapest first)

1. The chrome — the actual quest. Motif bevels and separators, a chunky button row, fixed-width labels, a menu bar that reads File Edit View Data, a status strip for RA/Dec / alt-az / time, colors from an 8-bit palette. A modern canvas wearing the 1993 window manager.
2. Stars. The HYG catalog (Hipparcos + Yale Bright Star + Gliese, ~120k stars) — pre-filter at build time to naked-eye and ship compact. J2000 positions precessed to the date of view, then projected.
3. Time and place. An observer (lat/lon), and a clock you can scrub — that is the ephemeris part: the sky tomorrow night, the sky on the night of 1993-12-01.
4. Sun, Moon, planets. astronomy-engine (MIT, pure JS): VSOP87/ELP2000, sub-arcsecond for the ten traditional planets over ~1700–2200 CE, with Horizon() for alt/az and rise/set/phase searches.
5. The XEphem extras, in order of payoff: coordinate-grid toggles · constellation figures · object list + info panel (the "you clicked a star, here's the catalogue entry" moment) · DSS imagery pull · and then stop — telescope control (XEphem drives Meade/Celestron hardware over INDI) is out of scope for the browser.

Stack notes (all free for this use)

Running the original locally (done 2026-09-28)

xephem/ in this repo runs the real thing in a container — same Motif widgets, same fonts, no admin password, viewable in a browser over noVNC:

cd xephem && docker build -t xephem-viewer . && ./fetch-data.sh
docker run --rm -p 6080:6080 -v "$PWD/share:/opt/xephem-share" --name xephem xephem-viewer
# → http://localhost:6080/vnc.html?autoconnect=1&resize=scale

It opens with the Sky View already up, the site set to Chicago, and 43 auxil files + catalogs staged. See xephem/README.md for the whole story.

The native macOS window (the nicer experience, one admin step): brew install openmotif openssl is done; run brew install --cask xquartz once (asks for your password), then xephem/run-native.sh fetches, builds and launches it as a real XQuartz window. Verified 2026-09-29 on this machine (Intel, macOS 26.6.2): 4.3.0 compiles clean against brew's Motif and links libXm/libXt/libXmu/libX11. groff turned out to be unnecessary — upstream lists it, but it only serves man pages and drags in ghostscript + tesseract + pango.

Three traps, paid for once so nobody pays again:

1. The Sky View aborts (SIGABRT) without auxil/. No message beyond auxil/logo.gif: No such file or directory; Sun/Moon/Earth views are unaffected, so it looks like a Sky-View bug. The GitHub tarball's auxil/ is partial — the rest (moon.fts, marsmap.fts, xephem_sites, xephem_skyhist, …) survives on an ESO mirror.
2. XEphem.SkyViewUp: 1 aborts at startup — the app's own saved-window-state resource kills the process before it draws. The Sky View has to be opened from the View menu.
3. make -j fails — upstream builds its bundled libs in the same pass as the final link, so a parallel make races into ld: cannot find -lastro.

And the site is configured by X resources, not a config file: XEphem.Sitename (default "Chicago, Illinois" with obviously wrong 0:0:0 coordinates), XEphem.Lat / XEphem.Long (+ north / + WEST, d:m:s), XEphem.TZone (hours behind UTC), and XEphem.ShareDir (where auxil/ and catalogs/ live).

The palette, from the program's own resources

Free gift for the rebuild — GUI/xephem/fallbacks.c gives the exact colors, so the browser version can be faithful instead of "90s-ish":

Planet tones too (moonColor #d9d9d9, marsColor #ffb568, saturnColor #efcb9e, …), and the sky's default trail state is SkyViewTrailState: 4 3 2 1 0 0 10 0 0.0.

Open questions (Rohan's call)

• Scope: just the Sky View, or the other XEphem windows too (Earth / Moon / Sun / planet views)?
• Local sky vs atlas: the sky above Chicago right now, or a free-floating chart you can pan to any date and place? (XEphem is both; the scrubber makes it cinematic.)
• How retro: Motif chrome around a crisp modern canvas (my instinct — readable and evocative), or full pretend-1993 with bitmap fonts and dithered 8-bit color?
• Where it lives: a public route, likely /sky, like /streets and /muscle-up. Confirm the route name.
• Naming: MIT means the name is usable with attribution, but this is its own thing — "xephem" as homage vs its own name is your call.
• Catalog depth: naked-eye (~9k stars, tiny payload) vs full HYG (~120k, still fine as binary).
• Is this a "learn the sky" tool or an art piece? It changes the answer to nearly every layout question above.

Status

Germ, plus a running original. Nothing of the rebuild exists yet — but the real XEphem 4.3.0 is now running locally in xephem/ (container, browser-viewable), so the UI can be studied directly instead of from screenshots. Page written 2026-09-28 from research and a live session with the program.

Sources

• XEphem — Wikipedia (lineage, 1993 first release, Motif, license history)
• XEphem/XEphem on GitHub (MIT since 4.0.0; releases 4.2.0 / 4.3.0; 2025 maintainership)
• Astronomy Engine (JavaScript) — MIT; VSOP87/ELP2000; accuracy window ~1700–2200 CE
• astronexus/HYG-Database — Hipparcos + Yale BSC + Gliese merged catalog
• d3-celestial — reference browser planetarium built on HYG-derived data
• three-starmap — three.js point-mesh star map (~8,900 naked-eye stars, 88 constellations)