Various types of artificial horizons have been used, including a bubble, gyroscope, and pendulum. Of these, the bubble This type of instrument is fitted as a backup system to inertial and other positioning systems in a few aircraft, fulfilling the requirement for a selfcontained, non emitting system. On land, a skilled observer using a 2-minute averaging bubble or pendulum sextant can measure altitudes to an accuracy of perhaps 2', (2 miles). This, of course, refers to the accuracy of measurement only, and does not include additional errors such as abnormal refraction, deflection of the vertical, computing and plotting errors, etc. In steady flight through smooth air the error of a 2-minute observation is increased to perhaps 5 to 10 miles.

At sea, with virtually no roll or pitch, results should approach those on land. However, even a gentle roll causes large errors. Under these conditions observational errors of 10-16 miles are not unreasonable. With a moderate sea, errors of 30 miles or more are common. In a heavy sea, any useful observations are virtually impossible to obtain. Single altitude observations in a moderate sea can be in error by a matter of degrees.

When the horizon is obscured by ice or haze, polar navigators can sometimes obtain better results with an artificial horizon sextant than with a marine sextant. Some artificial horizon sextants have provision for making observations with the natural horizon as a reference, but results are not generally as satisfactory as by marine sextant. Because of their more complicated optical systems, and the need for providing a horizontal reference, artificialorizon sextants are generally much more costly to manufacture than marine sextants.

Altitudes observed by artificial horizon sextants are subject to the same errors as those observed by marine sextant, except that the dip (height of eye) correction does not apply. Also, when the center of the Sun or Moon is observed, no correction for semidiameter is required.

• Parts and principle of the sextant - 2009-07-02 - 11:25:19
• Reducing Star Sights to a Fix - 2009-04-24 - 02:08:03
• Convert A Polaris Sight To Latitude - 2009-04-24 - 04:45:52
• Longitude at Meridian Passage - 2009-04-24 - 04:15:10
• Latitude at Meridian Passage - 2009-04-23 - 01:03:09
• Reducing A Planet Sight - 2009-04-23 - 12:37:29
• Reducing A Moon Sight - 2009-04-23 - 12:18:18
• Reducing A Sun Sight - 2009-04-23 - 11:56:15
• Celestial Body’s Amplitude - 2009-04-23 - 09:29:35
• Compass Error By Azimuth Of Polaris - 2009-04-23 - 09:11:02

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