That which is added to or subtracted from a reading, as of an instrument, to eliminate the effect of an error, or to reduce an observation to an arbitrary standard. |
That which is added to or subtracted from a reading, as of an instrument, to eliminate the effect of an error, or to reduce an observation to an arbitrary standard. |
Related Terms |
PRECOMPUTATIONThe process of making navigational solutions in advance; applied particularly to the determination of computed altitude and azimuth before making a celestial observation for a line of position. When this is done, the observation must be made at the time used for the computation, or a correction applied. |
NOCTURNALAn old navigation instrument which consisted of two arms pivoted at the enter of a disk graduated for date, time and arc. The nocturnal was used for determining time during the night and for obtaining a correction to be applied to an altitude observation of Polaris for finding latitude. |
REDUCTION TO THE MERIDIANThe process of applying a correction to an altitude observed when a body is near the celestial meridian of the observer, to find the altitude at meridian transit. The altitude at the time of such an observation is called an EX-MERIDIAN ALTITUDE. |
SEMIDIAMETER CORRECTIONA correction due to semidiameter, particularly that sextant altitude correction, when applied to the observation of the upper or lower limb of a celestial body, determines the altitude of the center of that body. |
ASSUMED LONGITUDEThe longitude at which an observer is assumed to be located for an observation or computation, as the longitude of an assumed position or the longitude used for determining the latitude by meridian altitude. Also called CHOSEN LONGITUDE. |
ASTRONOMICAL POSITIONA point on the earth whose coordinates have been determined as a result of observation of celestial bodies. The expression is usually used in connection with positions on land determined with great accuracy for survey purposes. |
AIR TEMPERATURE CORRECTIONA correction due to nonstandard air temperature, particularly the sextant altitude correction due to changes in refraction caused by difference between the actual temperature and the standard temperature used in the computation of the refraction table. The Nautical Almanac refraction table is based upo |
BAROMETRIC PRESSURE CORRECTIONA correction due to nonstandard baro- metric pressure, particularly the sextant altitude correction due to changes in refraction caused by difference between the actual baro- metric pressure and the standard barometric pressure used in the computation of the refraction table. |
ASSUMED LATITUDEThe latitude at which an observer is assumed to be located for an observation or computation, as the latitude of an assumed position or the latitude used for determining the longitude of time sight. Also called CHOSEN LATITUDE. |
BACK SIGHTA marine sextant observation of a celestial body made by facing away from the body, measurin |
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