Navigation: Charts Flashcards
What is true direction?
True direction is measured with reference to true north.
What is magnetic direction?
Magnetic direction is measured with reference to magnetic north.
Note: The magnetic north pole is near to the geographic true north pole but is not in exactly the
same place.
What is magnetic variation?
Variation is the difference between the direction of magnetic north and true north. It is therefore the
difference between all true headings and their corresponding magnetic headings at any point.
Variation is not a constant across the earth but varies in magnitude from place to place. Variation is
described as either east (plus) or west (minus).
What is compass direction?
Compass direction is measured with reference to compass north. Compass north is the deviated
direction away from magnetic north indicated by a compass needle
What is compass deviation?
Deviation is the difference between the direction of magnetic north and compass north.
What are the lines that run from pole to pole on the earth called?
Meridians of longitude run from pole to pole and converge at both poles.
Meridians of longitude are described by their angle away from the prime meridian, namely, the
Greenwich meridian. The units of measurement used to describe a meridian’s position are degrees,
minutes, and seconds, and they are named east or west depending on where they lie in relation to the
prime meridian. The maximum longitude of 180 degrees is known as the Greenwich antimeridian.
Additionally, meridians at 15-degree intervals in an easterly direction are classified as alpha to zulu.
The Greenwich meridian is known as zulu.
How do you measure a change of latitude?
A change of latitude, i.e., north-south distances, along a meridian of longitude is measured as 1
nautical mile equals 1 minute (60 minutes = 1 degree).
Note: North-south distances can be measured across a pole where points lie on opposite meridians
of longitude.
What are the lines that run east-west on the earth called?
Parallels of latitude run east-west on the earth.
Parallels of latitude are described by their angle above or below the equator. The units of
measurement used to describe a parallel of latitudes position are degrees, minutes, and seconds (1 degree = 60 minutes, 1 minute = 60 seconds). The maximum possible latitude is 90 degrees north or
south, i.e., north or south pole
How do you measure a change of longitude?
A change of longitude, i.e., east-west distance, (along a parallel of latitude) has a varied distance
(nautical miles) per degree at different latitudes. The distance along the equator is measured as 1
nautical mile equal to 1 minute. As we move away from the equator, the east-west distance (nautical
miles) decreases for the same change in longitude until eventually, at the poles, the distance between
the meridians has reduced to zero. Therefore, the change of longitude distance decreases as latitude
increases, and this is known as departure
What is departure?
Departure is an east-west distance along a parallel line of latitude, other than the equator, that
requires the use of the following formula to calculate the variable east-west distance (nautical miles)for a given change of longitude at different latitudes.
Departure (nautical miles) = change of longitude (minutes) × cosine of latitude
What is a great circle track?
A great circle track is a line of shortest distance between two points on a sphere (or a flat surface)
with a constantly changing track direction as a result of convergence
What is a rhumb line?
Rhumb lines are tracks with a constant track direction between two points on a sphere and therefore
must be a longer distance than a great circle track.
What is convergency?
Convergency represents the change of direction experienced along east-west tracks, except rhumb
lines, as a result of the way direction is measured due to the effects of converging meridians at the
poles. The change of direction experienced between two points is known as convergency.
Convergency is clearly dependent on latitude; it is zero at the equator, where the meridians are
parallel, and a maximum at the poles, where the meridians converge. It is also dependent on how far
you travel. A short distance traveled will have only a small change of direction, whereas a long
distance will have a large change of direction.
What is a conversion angle?
Conversion angle is the angle of difference in direction between the rhumb line and the great circle
track between two points and therefore is used to calculate a rhumb line direction given a great circle
track, or vice versa.
What is chart scale?
Scale is defined as the ratio of chart distance to earth distance
