Sextant
A modern logbook for celestial navigation and a sight-reduction calculator for
sailors, students, and anyone who wants to know where they are without GPS.
Enter an observation — the body, the precise UTC time of the mark, your
sextant altitude, your height of eye — and Sextant does the rest: almanac
lookup, altitude corrections (dip, refraction, semi-diameter, parallax),
intercept-method reduction, and an on-screen plotting sheet you can read
like the paper original.
Read the user manual · Privacy policy · Report an issue
What’s in the app
- Sun, Moon, Venus, Mars, Jupiter, Saturn, and the 57 nautical-almanac stars.
- Fully offline, always. Ephemerides computed from Meeus, VSOP87 and
ELP‑2000 algorithms — no almanac files to update, no yearly app refresh.
- Sync across iPhone, iPad, Apple Watch, and Mac through your private
iCloud database.
- Apple Watch companion. One tap on MARK captures the precise instant of
an observation, then syncs to your phone to finish the entry.
- AR sextant. Line up the body in your camera viewfinder and the device
records the altitude — handy when you don’t have a brass sextant aboard,
or for teaching.
- Five reduction modes — single Sights, Noon‑sight latitude, Polaris,
Running fix, AR — and a Star Chart for planning twilight observations.
- GPX / KML chart overlays for routes and waypoints on the plot sheet.
- No tracking. No advertising. No third‑party SDKs. Nothing leaves your
iCloud account.
Built for navigators who want the dignity of the mathematics, not the
seduction of a black box.
Getting started
- Download Sextant on the App Store.
- Open the app, tap Try a sample voyage on the empty Voyages screen —
you’ll get a complete demo “Hawaiian Passage” with three days of sights
you can poke at.
- Read the manual — a friendly tour of how celestial
navigation works and how to use every screen.