Astrolabe — AR Planetarium

Most sky apps can tell you that bright dot is Jupiter. Astrolabe tells you whether tonight is worth going outside for, which way to turn, and how long before it sets.

A precision AR planetarium built like an instrument.

■ THE SKY, THROUGH YOUR CAMERA
Raise your phone and the live viewfinder is overlaid with the sky computed for your exact time and place: 25,791 stars to magnitude 7.5, the Sun, the Moon with observer parallax, all eight planets from VSOP87, 88 constellations, traditional Chinese asterisms, deep-sky objects, the Milky Way and the galactic center at Sgr A*. Gravity and magnetometer give the camera's true bearing, corrected for magnetic declination, so labels land where the objects actually are. A transparency slider runs from pure camera, through blended AR, to a full star chart, and zoom drives the field of view.

■ POINT, DON'T JUST BROWSE
Pick a target and Astrolabe stops describing and starts directing. A centerd altitude/azimuth ring with a directional sector shows exactly which way to rotate until the object is in frame. Haptics confirm the moment you are on it: at night you look at the sky, not the screen.

■ TONIGHT, IN ONE ANSWER
The Observation screen opens with a single verdict: a score for tonight, the usable window between twilight and moonrise, and the one target most worth your time. Tap it and you are in AR navigation. Everything else stays folded away until you ask.

■ PLAN ANY NIGHT
The ephemeris lists every object with its altitude and azimuth right now, and expands in place into a 24-hour altitude curve with civil, nautical and astronomical twilight bands plus rise, transit and set times. Pick any date in the calendar and the sky recomputes. Scrub time by ±24 hours or run it forward and backward at up to 3600×.

■ ECLIPSES, DRAWN NOT STOCK
Eclipses are rendered frame by frame, not illustrated. Moon phase comes from the live ephemeris, not four fixed images. Total and annular differ because the disc either covers or leaves a ring of fire. A lunar eclipse turns copper inside the umbra — what reaches the Moon is sunlight refracted through Earth's atmosphere.

■ SATELLITES OVERHEAD
Orbits propagate with SGP4/SDP4, Stellarium's model, so the ISS and the rest of the catalog cross your AR sky in real time, with pass predictions for your location.

■ ASK THE ADVISOR
An AI observing advisor sits on the same engine and reads instruments instead of guessing: twilight stage, Moon altitude and illumination, Bortle class, naked-eye limiting magnitude, cloud, humidity, wind. Ask "is tonight any good?" or "what should I photograph?" and it answers with rise and set times, suggests focal length and aperture, then points the AR view at the target and sets the time for you. No sign-in; a free daily allowance comes with the install.

■ BUILT FOR DARK-ADAPTED EYES
Night-vision mode transforms the whole interface, not just the star chart, so changing screens will not throw a bright page at eyes that spent twenty minutes adapting. Twilight-aware colors, a light-pollution magnitude limit matched to your real sky, and monospaced readouts so live numbers stop twitching as they change.

■ EVERY SCREEN SIZE
Portrait and landscape; phones, tablets, foldables. Wide screens get a two-column observing layout, not a stretched phone one.

■ OFFLINE BY DESIGN
Star catalogs, ephemerides, planetary theories and orbital elements live on the device, so the sky computes with no signal — which is where the good skies usually are. Only the AI advisor needs a connection. No ads, no account, no purchases.

Astrolabe is named for the classical instrument that made celestial geometry something you could hold and navigate by. That is the design brief: data is the interface, the phone is the instrument, the sky is the answer.

Star data: HYG v4.3. Constellation lines: d3-celestial (BSD). Planets: VSOP87 with Schlyter elements as fallback. Satellites: predict4java (Apache 2.0). Portions derived from Stellarium data (GPL v2).