Whole-horizon sextants use a half-silvered horizon mirror to provide a full view of the horizon. They developed a technique that allowed them to work out the time by measuring the angle between the moon and a celestial here to be many mistakes.
An artificial horizon is useful when the horizon is invisible, as occurs in fog, on moonless nights, in a calm, when sighting through a window or on land surrounded by trees or buildings. At sea, results within several nautical miles, well within visual range, are acceptable.
Many navigators purchase weatherproof cases so that their sextant can be placed outside the cabin to come to equilibrium with outside temperatures. Move the sextant slightly so that the stars move to the other side of the field of view.
Traditional sextants have a half-horizon mirror, which divides the field of view in two. If the reflected and direct image of the horizon are in line there is no index error.
In both types, larger mirrors give a larger field of view, and thus make it easier to find a celestial object. Both smaller and larger instruments are or were in use: Index error This occurs when the index and horizon mirrors are not parallel to each other when the index arm is set to zero.
The exact time of the sight must also be noted simultaneously, and the height of the eye above sea-level recorded.
Bring the two stars into coincidence either to the left or the right of the field of view. Most had artificial horizons to permit taking a sight through a flush overhead window.
All of the above problems however can be taken out of the calculation using data found in almanacs and then applied to the answer Manu The arc of the sextant should appear to continue unbroken into the mirror.
With these, the navigator pre-computed his sight and then noted the difference in observed versus predicted height of the body to determine his position.
Sextants work by measuring the angle between any two objects that are visible. Sextants can be used very accurately to measure other visible angles, for example between one heavenly body and another and between landmarks ashore.
This system works by having between satellites orbiting the earth continuously. Then rotate the tangent screw back and forth so that the reflected image passes alternately above and below the direct view.
The standard frame designs see illustration are supposed to equalise differential angular error from temperature changes. This permits the use of the sextant at night when a backstaff is difficult to use.
The angle of the sight is then read from the scale on the arc, making use of the micrometer or vernier scale provided.Nautical Charts, Books, Navigation Software & Marine Supplies Welcome to Maryland Nautical Sales where you can purchase nautical charts, books and other navigational resources at 10 - 40% off.
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