Professional Navigation Teacher Interview Preparation Guide

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A Meridian is a Great Circle line which passes through the poles of the earth. A local Meridian is one that passes through the observer's local position. The Greenwich Meridian passes through Greenwich, England, and is defined as having 0° Longitude.

Sector Lights is light emitted from a single position which will show up as either red, white or green depending on the angle of the observer, designed to indicate a safe navigational area.

Limb is when taking a sun or moon sight it is difficult to guess where the center is so the observer aligns either the top edge (Upper Limb) or more usually the bottom edge (Lower Limb) of the object on to the horizon. The sight is then corrected using the appropriate correction tables.

Running fix is advancing a LOP or previous line of position forward to a current line of position. A fix based on two separated bearings of the same fixed object and the distance run between the bearings.

Local Noon is the time when the sun reaches its highest altitude at your position and is directly north or south of you. it will then be at your Zenith and its GHA will correspond to your longitude.

Celestial sphere is an imaginary sphere with the earth at its center, on whose surface the stars, planets and other heavenly bodies appear to be situated.

Snellius construction is a method for combining three compass bearings to obtain a position fix, one where magnetic variation and deviation need not to be taken into account.

ITCZ, Intertropical Convergence Zone is the varying area of normally still air lying approximately between 5⁰ north and south of the equator.

The Estimated Position is the latitude and longitude at which the observer estimates his position to be, before fixing his actual position with the use of a sextant.

Declination is the angular distance to a point on the celestial sphere measured north and south from the celestial equator along the hour circle.

Mercator projection is a method for representing the spherical globe as a flat map with lines of latitude and longitude intersecting at right angles. Devised by Geradus Mercato in 1569.

Cardinal Marks is buoyage marks indicating the direction of safe water with reference to the cardinal points.

International Date Line is the imaginary line in the Pacific Ocean at which the date changes. This line varies from the 180⁰ meridian to avoid populated land areas.

A plane through the centre of the earth intersects the surface of the earth on a Great Circle. So the centres of Great Circles are always at the centre of the earth.

Drying height is the height above chart datum, on a chart, of any areas which are uncovered at low water.

Course is the direction in which a vessel is heading or is intended to be steered, the direction through the water.

Quadrant is a precursor to the sextant as an instrument used to measure altitudes up to 90° or one quarter of a circle, hence the name. First proposed by Ptolemy as an improvement on the astrolabe.

Jetsam is are objects that have been thrown overboard from a vessel, originally stuff jettisoned by a ship which was in trouble.

Geographical Position or GP is in celestial navigation it is the point on the earths surface directly beneath the Zenith, and the bit of the surface you are standing on is your body’s Geographical Position or GP.

Conversion tables is used to convert units of one system to units in another.

Electronic logs or E log books is a method of standardising the keeping of logs digitally on commercial vessels.

Cocked hat is a triangle formed by a series of three LOPs which do not meet at an exact point.

Apparent wind is the wind as felt on board, this will be the actual wind modified by the wind created by the vessels movement.

Having passed through the vacuum of outer space, the light from the celestial body has to pass through the atmosphere before it is observed using a sextant. The atmosphere tends to bend the path of the light as it passes through, so that the celestial body appears higher in the sky than it would be if there was no atmosphere.

A calculated Altitude assumes the earth has no atmosphere, so the sextant Altitude has to be corrected for Refraction so that it can be compared to the calculated Altitude. Refraction tables are always included in Almanacs used for celestial navigation.

Azimuth is the horizontal angular distance from a reference position to a celestial body, usually measured clockwise in degrees from the direction of the nearest pole.