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Introduction
I
cebergs are bits of glaciers that have broken off into the sea. An iceberg has over
twice as much ice under the water.
Under the Ice
The great land masses of the northern
hemisphere
form the
edges of the Arctic Ocean, with North America to one side,
and Eurasia on the other. The gaps are nearly filled by
islands such as Greenland and Spitzbergen. The North
Atlantic and Bering Strait are the only way in by ship. Early
explorers in small wooden vessels braved these passages.
In 1977, a Russian nuclear-powered icebreaker was
able to push its way right across the Arctic Ocean, smashing
a track through the sea ice and reaching the North Pole.
Submarines have traveled beneath the ice, surfacing near
the North Pole through cracks in the ice.
T
he Arctic Ocean is covered by sea ice most of the year. This ice is always moving
and cracks suddenly open or close.
Lines on the Earth
The globe can be divided up by lines
encircling the Earth starting at the
Equator, which is exactly around the
middle, and going north and south.
These are called lines of latitude. And
it can be divided by lines running from
the North Pole to the South Pole. These
are lines of longitude. The point where
lines of longitude and latitude cross
gives an exact description of a position
on the globe.
Latitude was known to early Greek
and Arab navigators. They made simple
devices to measure the angle of the
Sun above the horizon at midday.
A calculation showed how many degrees
they were away from the Equator. The
Equator is 0° and if you travel north
your latitude gradually increases to 90°
at the North Pole. For each degree you
travel about 68 miles (110 km).
Confusingly, the same thing happens
when you travel south from the Equator.
Latitude must always have north (N) or
south (S) added to show which side of
the Equator you are. So, London is
51°N, and the North Pole 90°N. But
Sydney, Australia, is 33°S, and the
South Pole 90°S.
To work out the exact position,
degrees are broken down into
minutes
.
Just as there are 60 minutes in an hour,
so there are 60 minutes in a degree.
L
ines of latitude and longitude on the globe.