PERISCOPE SEXTANT

A sextant designed to be used in conjunction with the periscope of a submarine.

Related Terms

HEIGHT OF EYE CORRECTION

The correction to sextant altitude due to dip of the horizon. Also called DIP CORRECTION

height_of_eye_correction correction sextant altitude dip dip_correction sextant_altitude to_dip

INDEX PRISM

A sextant prism which can be rotated to any angle corresponding to altitudes between established limits. It is the bubble or pendulum sextant counterpart of the INDEX MIRROR of a marine sextant.

index_prism angle bubble sextant index_mirror prism

INDEX MIRROR

The mirror attached to the index arm of a marine sextant

index_mirror arm sextant index_arm

INDEX ARM

A slender bar carrying an index; particularly the bar which pivots at the center of curvature of the arc of a marine sextant and carries the index and the vernier or micrometer.

index_arm bar sextant vernier arc curvature

The error in the reading of an instrument equal to the difference between the zero of the scale and the zero of the index. In a marine sextant it is due primarily to lack of parallelism of the index mirror and the horizon glass at zero reading.

index_error instrument difference scale error sextant horizon horizon_glass index_mirror

IRRADIATION CORRECTION

A correction due to irradiation, particularly that sextant altitude correction caused by the apparent enlargement of the bright surface of a celestial body against the darker background of the sky.

irradiation_correction surface correction sextant altitude apparent celestial celestial_body sextant_altitude

SHIFT TIDES

Sighting the positions of the sun and moon using a sextant and using a nautical almanac to determine the location and phase of the moon and calculating the relative effect of the tides on the navigation of the ship

shift_tides sextant nautical_almanac phase ship relative almanac nautical

LIMB

1. The graduated curved part of an instrument for measuring angles, such as the part of a marine sextant carrying the altitude scale, or ARC. 2. The circular outer edge of a celestial body, usually referred to with the designation upper or lower

limb instrument sextant altitude celestial edge

AIR TEMPERATURE CORRECTION

A 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

air_temperature_correction temperature air difference standard correction nautical_almanac sextant almanac altitude nautical

ALTITUDE INTERCEPT

The difference in minutes of arc between the computed and the observed altitude (corrected sextant altitude), or between precomputed and sextant altitudes. It is labeled T (toward) or A (away) as the observed (or sextant) altitude is greater or smaller than the computed (or precomputed) altitude

altitude_intercept difference sextant t altitude arc observed_altitude