Longitude & Latitude
Longitude & Latitude ( Go To Top )
Once
your position is known the location can be determined in degrees of
latitude and longitude. Lines of latitude are circular
bands running east and west parallel to the equator. Lines of latitude are designated from zero to 90 degrees north and south
of the Equator. Lines of longitude are circular bands which run north
and south through the two poles. Lines of longitude are
designated from zero to 180 degrees east and west of the Greenwich
Observatory in London, England.
Degrees of latitude and longitude are divided into 60 minutes. Depending upon the chart, each minute of latitude is either divided into tenths or sixths (each division equal to 10 seconds). As measured on the Earth, lines of longitude converge on each other the further north one travels, as the distance between the lines of latitude stays the same. Thus, a minute of latitude (measured on the vertical scale of the chart) is used as the definition of one nautical mile. It should be noted that a flat chart will distort distances found on a round globe. Thus, always determine the distance of a nautical mile on the latitude scale which is closest to where you are charting.
To
measure the distance of your planned track, place your dividers on the
vertical scale of the chart and measure the distance of one nautical mile
by measuring the distance of one minute. Now walk your dividers down the track and measure its distance. View Video on How to Measure Distance
To
determine the direction of travel use the parallel ruler and the chart's
compass rose. Walk the ruler for the track to the compass rose and
read the direction in degrees True North or degrees Magnetic North.
View Video on How to Use a Parallel Ruler and
Compass Rose to Determine Direction
In the
Northern Hemisphere,
the north star can be used to roughly determine latitude. Using a
sextant, the degrees the star is above the horizon will roughly equal
the ship's position in latitude. The north star can be found at the
tail of the Little Dipper or by following the line produced by the two
stars on the cup of the Big Dipper.
The sun can also be used to
determine direction. In the northern hemisphere at 12:00 noon
shadows will fall to the north; in the southern hemisphere the shadows
will fall to the south.
More about early navigation methods (Mariners' Museum).
http://www.marinersmuseum.org/education/viking-ships
