What is a True Circumnavigation?
'[A] true circumnavigation of the world ...
where the track passes over 2 points antipodal to each other ... a circumnavigation
where the vessel passes through two points on the earth's surface which are diametrically
opposite each other ...'
Sir Francis Chichester, Gipsy Moth Circles the World, 1967.
THE FIRST CIRCUMNAVIGATION OF THE GLOBE passing through antipodal points
was completed in 1522 by 18 members of Ferdinand Magellan’s expedition to find a
route to the Spice Islands by sailing west. Magellan himself was killed en route
on the island of Mactan in present day Philippines.
EXPLANATION of TRUE CIRCUMNAVIGATION
The most efficient way to measure a true circumnavigation by any means of propulsion
is for the track to pass through at least one pair of antipodal points; two places
on the surface of the globe that are diametrically opposite to each other. To cross
a pair of antipodal points means automatically crossing and travelling the minimum
distance of the equator, and spending equal time in both northern and southern hemispheres
Any other attempt at quantifying a circumnavigation inevitably involves a complicated
concoction of criteria such as minimum distances, minimum number of oceans/landmasses
crossed, minimum meridians crossed etc and as such is inherently open to persistent
manipulation and dispute.
EXPLANATION of ANTIPODAL POINTS & GREAT CIRCLES
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To understand the significance of antipodal points in a true circumnavigation one
must first define a Great Circle: the largest circle which can be drawn on the surface
of globe by a plane cutting through the sphere at its centre. All longitudes (meridians)
are Great Circles because the plane cutting through every meridian of longitude
cuts through the centre of globe as well as the north and south poles.
Following a Great Circle inevitably entails crossing at least one pair of Antipodal
Points en route and as such is the only way of ensuring a fair circumnavigation
is achieved regardless of where on the planet the circumnavigation begins.
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If planes are put through the latitudes, only the one through the Equator will also
cut through the centre of the globe and therefore the Equator is the only latitude
which is a Great Circle.
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In practice, a sailing vessel cannot follow a Great Circle because of obstruction
by land masses. The most effective way to prove that a circumnavigation attempt
has followed a Great Circle is to put the plane through any point of the travelled
route and through the centre of the globe, and then to find the opposite point on
that plane – the point called the antipode. Simply put, if a sailing vessel’s track
crosses at least one pair of antipodes, the route approximates a Great Circle as
closely as possible and can therefore claim a 'true' circumnavigation.
This also ensures that:
The equator is crossed at least twice
a minimum distance of 22,600 nautical miles or more, equal or greater than the circumference
of the earth (or the length of the equator) has been travelled.
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HISTORIC PRECEDENT of TRUE CIRCUMNAVIGATIONS by SAIL
Magellan's ship Victoria (1522) - two pair of antipodes along the route
Sir Francis Drake's Golden Hind (1580) - four pair of antipodes along the route
Joshua Slocum's Spray (1898) - five pair of antipodes along the route
Sir Francis Chichester's Gypsy Moth IV (1967) - two pairs of antipodes along the
route
Sir Robin Knox-Johnston's Suhaili (1969) - two pairs of antipodes along the route
Chay Blyth's British Steel (1971) - two pairs of antipodes along the route