Navigation Teacher

Line Of Position, LOP is a line drawn on a chart on which the position of the vessel must lie. The line deduced from either a compass bearing of a mark or a sight reduction. A minimum of two or preferably more are necessary to establish a fix.

Fathom is an old fashioned unit of measurement to measure depth, approximately equal to 6 feet or 1.8 meters.

Course made good is the direction in which the vessel is actually traveling as opposed to the direction in which it is pointing. Corrections is alterations made to charts to update navigational information.

Celestial navigation is a method of navigating by referring to the stars or other objects in the sky.

The celestial body will be in one of four Azimuth Quadrants. If it is to the NORTH WEST, (Azimuth 0° to 90°), then it is in the NORTH WEST quadrant and so on for the SOUTH WEST, SOUTH EAST and NORTH EAST.

Altitude is the angular distance of a celestial body above the viewers horizon.

Beaufort Scale is a numerical method of describing wind strength.

Cross bearing is using LOPs from several navigational aids or marks to obtain a position fix.

First Point of Aries is a point on the celestial sphere which is used as a reference point, it is in fact where the ‘Ecliptic’ and the Celestial Equator cross.

Parallax is the apparent differences in the positions of objects viewed along different lines of sight.

Zenith is the point directly above the observer’s head.

Greenwich meridian is the Prime Meridian it is the 0°longitude line, it is referred to as the Greenwich Meridian because it passes through the Royal Observatory at Greenwich in the UK.

Civil twilight is times given in the almanac, for listed latitudes for approximately the best time to take a morning or evening sight, when both the horizon and the heavenly bodies are visible.

Aries is the constellation of the Ram in the Northern Celestial Hemisphere, see also, First Point of Aries.

Cardinal Points is the four main points of the compass, North, East, South and West.

Dip is a correction to be applied to sextant attitudes to compensate for height of eye above sea level.

Barometer is an instrument for measuring atmospheric pressure.

CMG is the Course Made Good is the course over the ground.

Deviation is the compass errors caused by metallic o magnetic objects on board the vessel.

South Magnetic Pole is the southerly point toward which a compass' needle always points, the south of the earth’s magnetic field as opposed to the geographic south pole.