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Geodesy - the Earth isn't flat!
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Until just a few hundred years ago, people believed that the Earth was
flat, and that if you kept moving in a straight line you would
eventually fall off the edge of it!
As early as the year 140 AD, Greek mathematicians began to develop
theories that the Earth was actually round. Ptolemy produced a map of
the spherical Earth at that time. However, the Greek mathematical ideas
didn't gain much ground in other areas of the world.
In medieval times the Christian Church found the view that the Earth
was not flat (with Heaven above and Hell below) heretical, and many
mathematicians and scientists of the time were imprisoned, and even
executed, for daring to suggest otherwise.
In the 14th, 15th and 16th centuries, explorers such as Columbus and
Vasco de Gama began to travel further and further afield. Finally, the
only surviving ship in the Portuguese explorer Ferdinand Magellan's
small fleet completed a circumnavigation of the globe in 1522, finally
proving conclusively that the Earth was in fact round.
After this period, a coordinate system developed, based around the
North and South pole of the Earth, whereby every position on the
Earth's surface could be defined by its latitude (or number of degrees
North or South of the Equator, half way between each of the Poles) and
its longitude, or number of degrees East or West of a defined line (or
meridian) running between the North and South Poles. For years, many
different lines of longitude were used as meridians and each country
had its own mapping scheme. Finally, in 1884, at a conference in
Washington DC, USA, 25 countries agreed that a meridian running through
the Royal Observatory in Greenwich, England, would be the "Prime
Meridian", from which all longitudes are derived.
But
It Isn't Round Either!
For hundreds of years, a round, or spherical, model of the Earth proved
to be enough to allow ships to navigate effectively. However, in the
19th century, geographers gradually began to realise that the Earth
isn't entirely round either! In fact, the globe is slightly flattened
at the poles and is wider at the Equator! This shape is called an
'ellipsoid', as it is shaped like a three-dimensional ellipse, or
near-circle. There is an entire field of study devoted to defining the
shape and size of the Earth and developing mathematical and geometric
models
for determining positions upon its surface. This field of study is
called
geodesy.
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