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Arctic
Circle is a circle of
latitude at 66° 33' North.
On summer solstice (in the
Northern Hemisphere), the Sun is
above the horizon at local
midnight time at all points in
this region.
Antarctic Circle is a
circle of latitude at 66°
33' South. On summer solstice (in
the Southern Hemisphere), the Sun
is above the horizon at local
midnight time at all points in
this region.
Azimuth is the measurement
in degrees of an arc along the
horizon from true north (0
degrees) to any position from 0
to 360 degrees.
Cardinal direction is
one of the astronomical
directions on the Earth's
surface: North, South, East, or
West.
Cartography is the science
and technology of map
production.
Compass is an device which
displays the direction of
magnetic North.
Declination (1) the angle
at the center of a sphere between
the equatorial plane and a line
to a point on a sphere. (2) The
arc between the Equator and a
point on a great circle
perpendicular to the Equator. (3)
The angular distance of a star or
planet above or below the
celestial Equator. (4) Magnetic
declination is the angle between
true (geographic) north and
magnetic North (the direction of
the magnetic compass needle).
Magnetic declination varies for
different locations because of
variation of the magnetic north
pole.
Equator is the central
circle of the Earth (0 degrees
latitude) that divides Earth in
half, North and South.
GMT Greenwich Mean Time is
the time zone for Greenwich
England, also known as Universal
Coordinated Time (UTC) and
Zulu.
Great Circle is a circle
created by any plane which passes
through the center of a
sphere.
Heading is the direction
you are traveling.
International Date Line is
a line on the Earth running from
the North to South Pole generally
following the 180° meridian,
measured from the Prime Meridian.
Neighboring regions on either
side of the line differ by one
day.
Latitude is the angular
distance north or south from the
earth's equator measured 0
through 90 degrees.
Longitude is the distance
parallel to the earth's equator
from the prime meridian usually
given in degrees.
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Minute
is 1/60th of a degree or 1/60th
of an hour.
Nautical Mile is 1/60th of
a degree of a great circle and
the defined length of a knot (One
Nautical mile per hour). One
Nautical Mile equals 1.150779
English/US Mile (Statute
Mile).
North Pole is 90 degrees
latitude North representing where
the Earth axis intersects the
surface of the Northern
Hemisphere.
Prime Meridian runs
through the original site of the
Royal Observatory at Greenwich,
England, which is defined as 0
degrees longitude along a great
circle around the earth. Also
known as the Greenwich Meridian
or International Meridian where
Zulu Time occurs.
South Pole is 90 degrees
latitude South representing where
the Earth axis intersects the
surface of the Southern
Hemisphere.
Time Zone is a
geographical region where time
was defined in 1884 to be the
same in 24 one-hour regions of
the world. Each zone having a
width of 15 degrees (24 X 15
degrees = 360). Each country is
responsible for its own time zone
definitions and considerable
variations have occurred since
the original definition.
Tropic of Cancer is
the latitude of 23° 27'
north, where the Sun reaches its
greatest northerly declination
(or summer solstice, for the
Northern Hemisphere) about June
21 (the start of summer and the
day with the longest daylight in
the Northern Hemisphere.
Tropic of Capricorn is the
latitude of 23° 27' south,
where the Sun reaches its
greatest southerly declination
(or summer solstice, for the
Southern Hemisphere) about
December 21 (the start of summer
and the day with the longest
daylight in the Southern
Hemisphere.
UTC is Universal
Coordinated Time, which is the
time at the prime meridian (0
degrees longitude) and is useful
as a standard for scientists and
navigators for avoiding the
confusion of time zones. Also
known as Greenwich Mean Time
(GMT) and Zulu.
Zenith is the point
directly above an observer,
forming a line from the center of
Earth, through the observer to
the point overhead.
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