Compass Observation App

Compass error, Gyro error, sight reduction & AR star finder for mariners.

Compass Observation App is a celestial-navigation and compass-checking toolkit for deck officers, watchkeepers, yachtsmen and students of navigation. Enter your position and UTC time and it computes 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 sextant sight, build a deviation card, and find your way around the sky.

Everything runs on the device and works fully offline — no signal needed at sea.

COMPASS ERROR
• Gyro and standard/magnetic compass error from an azimuth of any celestial body, in real observation-book order.
• Automatic true bearing, compass error, variation and deviation.
• Editable variation — use the chart value or the built-in World Magnetic Model.
• SOLAS gyro-error and 5° deviation cautions.
• Save readings to the logbook or a deviation card.

SIGHT REDUCTION (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 to plot.

DEVIATION CARD (Swing Ship)
• Record deviation at any heading and build a proper deviation card.
• Smooth deviation curve with A–E coefficients; read the deviation at every heading.
• Delete or replace readings; export a clean PDF report.

STAR DOME & AR SKY FINDER
• Live sky view that rotates with your phone's compass, with pinch-zoom.
• Full star field, accurate Moon phase, twilight-aware horizon, and a constellation lines/names toggle.
• AR mode overlays stars, planets and the real (moving) Milky Way on your camera, with on-device alignment calibration and a "GoTo" pointer for any body.

LOGBOOK
• Persistent history of compass checks and sights, with headings and position.
• Filter, view details, undo deletes, and export to CSV.

BODIES & DATA
• Sun, Moon, all seven planets, the 57 Nautical-Almanac stars and Polaris, plus a background star field and the 88 constellations.
• 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 — carried through to the sky views.

Positions are computed with established astronomical theory (Meeus / VSOP87 / ELP-2000), agreeing with reference ephemerides to a few arcseconds — comfortably within sextant precision.

Please note: this app is a navigation aid and practice tool. It is not a legal replacement for the official Nautical Almanac or approved navigation equipment. Always cross-check with official publications and keep a proper lookout.