COMING SOON

A celestial navigation app from Hartshorne Marine

Celestial navigation on your phone. No signal needed.

I've done a lot of ocean miles, and I've seen GPS let people down: a lightning strike, a flat battery, a wet plug. The sextant still works. This app is the almanac, the workform and the plotting sheet in one, for when you want to check your position the old way, or when you have to.

What it does

  • Plans your sights. Enter your DR, the date and your height of eye to get sunrise, sunset, civil and nautical twilight and noon, plus the stars and planets you'll see, with altitude, bearing and the sextant reading to preset.

  • Keeps the time. A chronometer log and a big one-thumb MARK button. It logs the watch error and daily rate and corrects every sight for you.

  • Every correction, line by line. Laid out like the workform you learned on, with intercept, azimuth, a computed fix, running fixes and noon latitude.

  • Built for sea. Works fully offline with no account, no sign-in and no tracking. A red night mode keeps your night vision.

  • A PDF sight log. The full working for each sight, plus the fix and a plot.

Accuracy: the almanac is computed from NASA JPL DE440 and the ESA Hipparcos star catalogue. Across more than 4,700 comparisons with the US Naval Observatory's almanac, the worst difference was 0.11 minutes of arc.

Who it's for

Small adventurous sailboats, bluewater cruisers, ocean passage makers, offshore racers and Yachtmaster Ocean students. Anyone who carries a sextant and wants to use it.

Planned for iPhone and Android.

Guide only

This app is a navigation aid and a guide only. It doesn't replace the Nautical Almanac, sight reduction tables, a proper lookout or good seamanship. Check your sights by hand before you rely on them, especially near land, and always check the rules for any exam or race.

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