Sextant — Celestial Nav

A complete celestial navigation toolkit for sailors, students, and the curious.

When the GPS quits, the sun, moon, planets, and stars still work. Sextant takes you all the way from a single sextant reading to a line of position on a map — with every correction shown, so you can check the math by hand if you want to.

Point the camera at the sky
The Sky tab labels every navigational body in view — the sun, the moon, all four navigational planets, and 58 navigational stars — using the magnetic compass and on-device ephemeris. Spot a star, tap its name, and a sight starts with that body identified and the time stamped.

Sight with your camera, or a real sextant
The camera flow measures altitude along the camera's line of sight from the phone's gravity sensor and shows how upright you're holding it. Multi-shot mode takes a series and saves the trimmed mean. Or just type your altitude from a brass sextant and let the app do the reduction.

Every body you'll ever shoot
Sun, moon, all four navigational planets — Venus, Mars, Jupiter, Saturn — and all 58 standard navigational stars. Positions computed from astronomical theory (VSOP87 for the Sun and planets, ELP-2000 for the Moon, star positions with precession and proper motion), not stale tables, and tested against U.S. Naval Observatory data. Works fully offline.

Noon Sight in one tap
Take the sun's altitude at meridian passage; the app gives you latitude. It also predicts the exact UTC of local apparent noon so you know when to look.

Plot your fix
Every sight draws a line of position on a real map. Take more than one, apply dead reckoning between them, watch your running fix come together — exactly like the paper-chart workflow.

Tools sailors actually use
- Polaris one-shot latitude
- Solar Compass — true bearing of the sun, for compass deviation checks
- Starfinder — what's above the horizon right now
- Reduction tables (dip, refraction, semi-diameter)
- DMS / decimal converter

Learn celestial navigation as you go
Step through your first sight with a guided walk-through. Every screen has inline help, and every correction in the sight reduction — dip, refraction, semi-diameter, parallax — has an explanation a tap away. Check the app against your hand calculations, or let it do all the work.

Share your work
Export sight records as CSV or as a printable PDF work-form in the classic HO 229 layout.

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