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• Dead ahead, through the pitch-black night, the
captain sees a light on a collision course with his ship.
He sends a signal: "Change your course ten degrees
"Change yours ten degrees west," comes the reply.
The captain responds, "I'm a United States Navy
captain! Change your course, sir!"
"I'm a seaman second class," the next message
reads. "Change your course, sir."
The captain is furious. "I'm a battleship! I'm not
changing course!"
"I'm a lighthouse. Your call."
How do we know where we are?
You are here. Huh?
When people first started going out in
boats they tended to stay close to shore
so they could use landmarks to guide
As people ventured further (the
Hawaiians 3000BC could travel over
1000km between islands) they needed to
find other landmarks so they turned to
the stars.
Celestial navigation
• The pattern of
stars and planets
seen from Earth
are constant in
The celestial
• It is useful to be
able to precisely
specify positions
on the celestial
• The North Celestial
Pole is the point on the
celestial sphere directly
above the Earth's North
Similarly, the South
Celestial Pole is directly
above the Earth's South
• The star Polaris, in the
constellation Ursa Minor,
is located very close to
the North Celestial Pole.
Polaris is therefore also
called the North Star.
Tools of the trade…
• Sexton: measures the angle between celestial bodies
and the Earth to determine position.
• Compass: Point to magnetic North, so you can follow
a course by knowing our position in relation to North.
• Loran C: radio transmissions from set positions on
the surface of the Earth, that triangulate to give you a
• GPS: is a worldwide radio-navigation system formed
from a constellation of 24 satellites and their ground
• a device that
measures the angle
between two objects.
It uses the position
of stars to find
latitude & longitude.
Loran C
• LORAN-C was originally developed to provide radionavigation service for U.S. coastal waters and later all
of the continental U.S.
• Twenty-four U.S. LORAN-C stations work in
partnership with Canadian and Russian stations to
provide coverage in Canadian waters and in the
Bering Sea.
• LORAN-C provides better than 0.25 nautical mile
absolute accuracy.
• Loran-C is a low frequency/long wave electronic
position fixing system using radio signals
transmissions @ 100 KHz from 3 or more
transmitters, linked in a chain. It gives a latitude and
longitude readout position to marine, aero and land
The Global Positioning System (GPS)
• The GPS is a worldwide radio-navigation system formed
from a constellation of 24 satellites and their ground
• GPS uses these "man-made stars" as reference points to
calculate positions accurate to a matter of meters (or
better than a centimeter in advanced models)!
• GPS receivers are becoming very economical, which
makes the technology accessible to virtually everyone.
• These days GPS is finding its way into cars, boats,
planes, construction equipment, movie making gear,
farm machinery, balloons, and even laptop computers.
What happens when you are
not a good navigator!!!