Compass Observation App is a celestial-navigation and compass-checking toolkit for deck officers, watchkeepers, yachtsmen and students of navigation. It turns your position and the UTC time into the true bearings, altitudes and rise/set times of the Sun, Moon, planets and navigational stars — so you can check your gyro and magnetic compass, reduce a sight, build a deviation card, and find your way around the sky.
Everything is computed on the device and works fully offline — no signal required at sea.
Everything a watchkeeper needs
From a single azimuth to a full deviation card — every tool speaks the language of the bridge.
Check gyro & magnetic error
- Work out gyro and magnetic/standard compass error from an azimuth of any celestial body.
- Automatic true bearing, compass error, variation and deviation.
- SOLAS gyro-error and 5° deviation cautions.
- Save readings straight to the logbook or a deviation card.
Intercept method
- Enter sextant altitude (Hs), index error, height of eye and limb.
- Get observed altitude (Ho), calculated altitude (Hc), azimuth (Zn) and the intercept — toward or away — ready for plotting.
Swing ship
- Record deviation at any heading and build a proper deviation card.
- Smooth deviation curve with A–E coefficients so you can read the deviation at every heading.
- Delete individual readings and export a clean PDF report (vessel, date, adjuster, notes).
Sky finder
- Live sky view that rotates with your phone’s compass, with pinch-zoom and manual mode.
- Full star field, accurate Moon phase, twilight times and a “GoTo” pointer for any body.
- AR mode overlays the stars and planets on the live camera — or a galaxy backdrop — to help you identify what you’re looking at in the real sky.
Persistent history
- Persistent history of compass checks and sight reductions with position, time and headings.
- Export everything to CSV or save to your device.
The whole almanac
- Sun, Moon, Venus, Mars, Jupiter, Saturn and the 57 Nautical-Almanac navigational stars (plus Polaris).
- Rise, set, transit and civil/nautical/astronomical twilight times.
- Magnetic variation from the World Magnetic Model.
Built for the bridge
- Manual position/UTC entry or GPS.
- Light, dark and a red night-vision theme to protect dark adaptation on watch.
Sextant-grade computation
Positions are computed with established astronomical algorithms (Meeus / VSOP87 / ELP-2000), including nutation, aberration, refraction and topocentric parallax — agreement of a few arcseconds for the Sun, planets and stars and sub-arcminute for the Moon, comfortably within sextant precision.