Module 1 • Arctic Exploration: Navigation
Teacher Notes 1-2a
Graticule
Latitude (lat.) is the angle between any point
and the equator. Lines of constant latitude
are called parallels. They trace circles on
the surface of Earth, with each pole being 90
degrees (North Pole 90° N; South Pole 90° S).
The equator, an imaginary line that divides
the globe into the Northern and Southern
Hemispheres, is located at 0° latitude.
Longitude (long.) is the angle east or
west of an arbitrary point on earth: The
Royal Observatory, in Greenwich, England
is the international zero-longitude point
(long.=0 degrees). The antipodal meridian of
Greenwich is both 180°W and 180°E. Lines
of constant longitude are called meridians.
The meridian passing through Greenwich
is the Prime Meridian. Unlike parallels, all
meridians are halves of great circles, and
meridians are not parallel: they intersect at
the north and south poles.
By combining these two angles, the horizontal position of any location on Earth can be specified.
For example, Baltimore, Maryland (in the United States) has a latitude of 39.3° North, and a longi-
tude of 76.6° West (39.3° N 76.6° W). Therefore, a vector drawn from the center of earth to a point
39.3° north of the equator and 76.6° west of Greenwich will pass through Baltimore.
This latitude/longitude “webbing” is known as the common graticule.
Traditionally, degrees have been divided into minutes ( _ ) and seconds ( _ ). There are several formats
for degrees, all of them appearing in a lat.-long. order:
DM Degree:Minute (49:30.0-123:30.0)
DMS Degree:Minute:Second (49:30:00-123:30:00)
DD Decimal Degree (49.5000-123.5000), generally with 4 decimal numbers.
To change from DM or DMS to DD, Decimal degrees = whole number of degrees, plus minutes divided
by 60, plus seconds divided by 3,600.
Source: http://en.wikipedia.org/wiki/Geographic_coordinate_system
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