Cover the camera with a solar filter before you aim at the sun, and never look at the sun yourself. Aim with the screen.
A clip-on solar filter for your phone is highly recommended to keep your phone’s camera safe.
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The phone’s sense of gravity stands in for the horizon. The camera finds the sun or moon, the clock times the sight, and two or more sights cross to give your latitude and longitude.
Version 1.0.15
Take a bearing of the sun, moon, a planet or a star with your ship’s or hand-bearing compass. The app knows its true bearing, so it gives your compass error and, with the chart variation, the deviation.
Reduce a made-up sight from somewhere at sea, the way you would by hand, then check your answers. Every exercise is real sky: the body, time and place are consistent with the almanac.
Enter a sight taken with a real sextant. It joins your other sights and goes into the fix.
Corrections applied: index, dip (sea horizon), halving (artificial horizon), semi-diameter (sun and moon limbs), and refraction and parallax in the comparison with the almanac.
Take a photo with your camera app, using any lens including 0.5×, with the sea horizon and the sun or moon in the same picture. Or load one you’ve already taken. The app finds the horizon and the body in the photo and measures the angle between them, using the time stored in the photo.
360 cameras work too: load the stitched 360 photo (or a fisheye picture) and the app finds the horizon all the way round. Run a Star check on a night 360 photo once to measure how true the camera’s geometry is.
A solar filter hides the horizon, so sun photos have to be taken without one. Keep it to a single quick shot, and never look at the sun. The moon needs no filter.
Measures the accelerometer’s built-in offset. Turning and flipping the phone cancels any slope in the surface, so a kitchen counter works. Each measurement starts by itself once the phone has settled. The bubbles show how level the phone thinks it is; green means within a quarter degree, though the calibration works on a gentle slope too. On a slope the bubbles swap sides after the half turn; that’s expected, and it’s how the slope gets canceled.
Measures the camera’s field of view and distortion. These matter most in horizon mode, and whenever the body sits away from the center. With the filter on, press Start, then move the phone slowly so the sun drifts from the top of the picture to the bottom and out toward the corners, for 15 seconds or so. Press Stop when done. Each camera and zoom setting is calibrated separately.
Why. Any small error in the app’s idea of the lens is zero at the center of the picture and grows toward the edges. The sweep measures it, so off-center sights become trustworthy.
Before you start. Steady sunshine, solar filter over the camera, and the lens or zoom you want to calibrate selected. Plant your feet; move the phone with your arms. Press Start lens sweep: the sheet closes and the Sight button becomes Stop.
Step 1: top to bottom. Aim just below the sun so it sits near the top of the picture, then tilt the phone up slowly, over about five seconds, so the sun drifts down through the center to the bottom.
Step 2: the corners. Tilt and turn together so the sun travels from one corner, through the center, to the opposite corner. Then do the other diagonal. The corners are where distortion shows.
Step 3: watch the progress, then Stop. The top of the screen shows frames, how much of the height you’ve covered, and how far toward the corners. It needs at least 60 frames and 45% of the height; aim for 80% of the height and 70% to the corner, usually 15 to 20 seconds. Press Stop; it also stops by itself after 30 seconds.
Step 4: the result. Three rising beeps and a message such as “field of view 66.4°, distortion −0.021, scatter fell from 8.3′ to 0.9′.” Scatter is how much the sun’s altitude wandered as it moved around the picture; the drop is the improvement. “No improvement found” means the lens was already right or the sweep was too small or jerky, and the old settings are kept.
Go slowly, keep the sun in the picture the whole time (frames where it leaves are skipped), and don’t walk. At night a Star field sight does this automatically, and even better.
Catches what is left: the camera sitting slightly crooked against the sensor, lens centring, and residual tilt. Set a reference position in Settings, take several sights there, then measure. Level and horizon sights get separate corrections.
Sextant measures how high the sun or moon stands above the true horizontal, using gravity in place of the sea horizon. Each sight puts you somewhere on a circle on the Earth. Where the circles cross is your position.
Put a certified solar filter (eclipse-viewer film or glass) over the camera before aiming at the sun, and keep it there. The lens focuses sunlight onto the sensor whether or not the picture looks dark, so darkening the exposure does not protect it. Zoomed or telephoto lenses are at most risk. Never look at the sun directly or through any optics. The moon needs no filter.
A clip-on solar filter for your phone is highly recommended to keep your phone’s camera safe.
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Install Sextant from the menu while you have signal; after that it works with none. Under way, set your course and speed in Fix to get running fixes. Night red mode keeps your eyes dark-adapted for star sights, and Compass check gives compass error and deviation from any body.
Almanac gives GHA and declination for any body and time, with an hourly table like a printed almanac page. Each sight in the list has a Working button that shows its reduction step by step. Practice makes up sights for you to reduce by hand and checks your answers. Logbook keeps your fixes on an offline map, shows how each method measures up against your reference position, and exports GPX or KML or printable reduction forms.
At night, choose Sky, then Star field, and aim at any patch of sky with several bright stars. The app recognizes the stars from their pattern, labels them, and takes a sight on every one at once. Give it a rough position (under Sky) so it can tell symmetric patterns such as Orion from their mirror image. The stars also check and refine the lens calibration.
The moon moves against the stars by about its own width each hour, so the angle between the moon and a planet or bright star tells the time. Choose a Moon–body pair under Sky and get both in the picture. Each lunar distance reports how far off your clock is, and the fix solves for the clock error along with your position. Close pairs are the most accurate: an error of 0.1′ in the angle is roughly 12 seconds of time.
At sea, switch to Horizon and hold the sea horizon and the body in the same picture. The app finds the horizon line and measures the angle up to the body, as a sextant does, so tilt and sensor error drop out. Set your height of eye in Settings and calibrate the lens first. A solar filter hides the horizon, so live horizon mode suits the moon best. For the sun, use a single Photo sight (in the menu) taken without the filter.
Each minute of altitude error is one nautical mile of position error, so steadiness and calibration decide the accuracy. Expect a few to a few tens of miles.
An odd.place experiment by Jason Buchheim.
Version 1.0.15, installed 2026-11-06 02:12 UTC
The camera stopped sending pictures.