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The diagram shows the winter conditions in the northern hemisphere - and is based on a real satellite
image taken by the GMS orbiter above the Pacific Ocean on November 30th 1998
(to see the original image click the diagram above).
The plane of the Earth's orbit around the Sun lies at an angle of
23½° to the rotational axis of the Earth (the imaginary line -
North/South - around which the Earth spins). As the Earth moves around the
Sun in its year long orbit, the Sun appears to drift northwards during our
summer and south during our winter. On December 21st, the Sun reaches its
maximum southerly position. On this day, the Sun will appear to be directly
overhead to anyone standing along a line around the world at 23½°S
- the Tropic of Capricorn. Each day after this the Sun will seem to be
overhead a little further north, on March 22nd it will appear overhead to
anyone on the Equator then on June 21st it will appear overhead at
23½°N - the Tropic of Cancer.
Print out the larger image of the Earth - measure the angle between the North/South line and the line of the shadow
across the globe.....
Is it nearly 23½°?
In the far south of Antarctica (at the South Pole), the Sun will never drop below the horizon during December and January. There
will be 24 hour daylight with the Sun travelling right around the sky - dropping towards the southern horizon during what passes
for night! Look at the diagram - as the Earth rotates, the area below the lower blue line will never experience total darkness.
In the far north, in the north of Norway, Greenland, Siberia etc, the complete opposite will be true. In December, the Sun is so low
in the sky that it never climbs above the southern horizon - even at mid-day. A dim grey light is all that changes night into day - and
if weather conditions are poor then there is likely to be no difference at all between night and day.
In the north, the low altitude of the Sun means that heat energy arriving at the Earth is spread over a large area - and the heating effect is
low. Northern temperatures fall - and by mid-winter there will be ice and snow, maybe even across parts of the UK!
In the south, the strong solar radiation means higher temperatures and the heat and dust of summer across Australia and southern Africa. Christmas
in the southern hemisphere is not ice and snow - it is summer and their Christmas carols are different!
Check out these two versions of an old favourite - one from the cold winter of the north and one from the hot dry Christmas summer of Australia.
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