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Astrolabe is an instrument used to determine the altitude of celestial objects before the introduction of the sextant. The first recorded use by Greek astronomers in around 200 B.C.

The Local Hour Angle (LHA) is the angular distance to the Meridian of the celestial body's Geographical Position, as measured Westwards from the observer's local Meridian.

The Local Hour Angle is calculated from the Greewich Hour Angle (GHA) of the celestial body and the Longitude of your Estimated Position in the following way:-

☛ LHA = GHA - Longitude, if the Longitude is West

☛ LHA = GHA + Longitude, if the Longitude is East

CC or Compass Course is the course to steer which has been corrected for current, variation, and deviation.

Copernicus is 1473-1543, Polish astronomer credited with disproving the Ptolemaic System.

Doldrums is the Inter-tropical Convergence Zone (or ITCZ) a belt of very still air between 5 degrees north and 5 degrees south of the equator.

Horizon is the apparent line, for an observer where the earth’s surface and the sky meet. Also a circle formed on the celestial sphere by a plane tangent to a point on the Earth's surface.

North Magnetic Pole is the northerly point toward which a compass' needle always points, the north of the earth’s magnetic field as opposed to the geographic north pole

Standard port is a port for which the Tide Tables give full details and from which Secondary Port details con be extrapolated. Strait is a narrow channel of water connecting two larger bodies of water.

Actual depth is the true depth of water as opposed to a predicted depth. Tidal height from table added to the charted depth.

If sight of the natural Horizon is not available, an Artificial Horizon is some means by which an observer can refer to a horizontal plane through his position. With a marine sextant, it is common to use a mirror in the horizontal plane. The angle between the celestial body as seen in the sky and as reflected in the mirror is measured with the sextant. Halving this angle gives the Altitude of the celestial body above the Horizon.

Bearing is the compass reading taken of a object in relation to the observer.

Compass Rose is is a design on a chart that shows direction. It points which way is north, south, east, west, and some intermediate directions.

Drift is the speed in knots of the effect of current or tide on a vessel's progress.

Horizon Glass is or Horizon Mirror half clear glass half mirror, on a sextant it allows the observer to view the horizon at the same time as a reflection of whatever is showing in the Index Mirror. Read more:

Ptolemy is Claudius Ptolemaeus, c. AD 90 to c. 168 a Roman mathematician, astronomer, geographer, possibly of Greek or Egyptian origin.

Almanac is an annual publication containing Tide Tables astronomical ephemerals etc.

The Greenwich Hour Angle (GHA) is the angular distance to the Meridian of the celestial body, as measured Westwards from the Greenwich Meridian (0° Longitude, also called the Prime Meridian).

Crux is the Southern Cross a constellation seen in the southern hemisphere.

Anabatic Winds is caused by warm air rising up a slope to be replaced by cooler air, as opposed to kabatic, descending winds.

Westerlies is are the prevailing west-to-east winds of the middle latitudes of both hemispheres on Earth.