How to Use a Nautical Sextant

Pull down the shade lenses of your sextant if you will be navigating by the sun. These shades protect your eyes from harm when you look at the sun, as the telescope of a sextant will intensify the brightness two to three times. Pull down all the shades until you determine the level of protection you will need. Skip this step if you will be navigating by the moon or a star.

Loosen the micrometer head and slide it back along the sextant's arc until it reads zero degrees.

Look through your sextant's telescope and focus on a celestial body.

Slowly slide the micrometer along the arc. As you slide the micrometer, follow the celestial body down toward the horizon.

Once you have leveled the celestial body with the horizon, fine-tune the micrometer until the celestial body is as close as possible to the horizon line. Take the reading when your vessel is at the crest of a wave to ensure you are viewing the true horizon, not the crest of another wave. This might take several minutes of adjusting to catch the perfect point.

Check the time, or have an assistant check the time the moment you level the celestial body with the horizon. Check the reading on the arc and micrometer drum for the exact angle of the celestial body when you took the time. Use a nautical chart to determine your location.