Locating Positions on Earth
Coordinate Systems
Earth scientists use the
latitude-longitude coordinate
system to identify locations on
Earth’s surface. Latitudes and
longitudes are measured in
degrees (°) and minutes (‘).
Each degree (°) is made up of
60 minutes (‘).
Sydney, Australia =
34°0’S, 151°0’E
Latitude
The equator (0°) marks
the middle of the Earth
–halfway between the
North and South poles.
Latitude
The latitude of any
point on the Earth is
the angular
measurement
between the location
and the equator
using the center of
the Earth as a focal
point.
Latitude measurements
above the equator are
referenced with an “N” for
Northern Hemisphere.
Latitude measurements
below the equator are
referenced with an “S” for
Southern Hemisphere.
Measuring Latitude
Scientists may use the position of stars in the night
sky to determine the latitude of their position on the
Earth’s surface.
Polaris (The North Star) is seen by observers in the
Northern Hemisphere. The star is positioned in the
night sky nearly directly over the North Pole.
Measuring Latitude
A sextant is an instrument used by an observer to
determine the angle between Polaris and the
horizon.
Pointer stars in the “Big Dipper” constellation
allow the viewer to find Polaris .
Polaris
observer
horizon
Longitude
The prime meridian (0°)
marks the middle of the
Earth –halfway between
the Eastern and Western
Hemispheres.
Longitude
Western
Hemisphere
Eastern
Hemisphere
The meridian that passes
through Greenwich,
England has been
designated as the prime
meridian (0°).
The longitude of any location
on the Earth’s surface is the
number of degrees between
the location and that of the
prime meridian.
Longitudes increase east and
west from the prime meridian
to the International Date Line
(180°)
Longitude
measurements
east of the prime
meridian are
referenced with
an “E” for
Eastern
Hemisphere.
Longitude
measurements
west of the prime
meridian are
referenced with a
“W” for Western
Hemisphere.
Measuring Longitude
The longitude of a position on
Earth’s surface can be
determined if one studies the
rate of Earth’s rotation over
time.
0°
12 pm
Measuring Longitude
Scientists will use GMT =
Greenwich Mean Time as a
means by which to gauge
the local time and location
of longitude for an
observer.
For example, if the sun has
reached its highest altitude
in the sky (local noon – 12
pm) at Greenwich, it will be
11am at 15° E and 1pm
15°W.
15°E
1 pm
15°W
11 am
Remember*** The
Earth rotates from
west to east at a rate
of 15° per hour.
Measuring Longitude –
Sample Problem
“If it 6 pm at Greenwich England, at
which location would it be 10 pm?”
D
B
A
C