Time differences in the world.

The Earth turns once around
the sun during one year.
Our planet is tilted and
also turns around her
own axis.
Due to the fact that the Earth
also turns around her own axis,
the most territories
come in the daylight of day
for some time
and in the dark of the night
for some time.
In June, the days on the
northern hemisphere are longer
than the nights on the southern
hemisphere. It's just
the opposite.
By the equator the day is
as long the night.
The sun rises at six o'clock
and sets in the
evening again at six o'clock.

It can't take place at the same time
all over the world because
the earth also turns around
her own axis.
At the end of the 19th century
the world was divided into
24 time zones, each 15
degrees wide. The lines on the
border of zones are called
meridians.
The meridian of Greenwich,
UK, is the zeropoint of the
zonecounting and the
zones are counted from
0 until 23 eastwards.
The sun passes the meridian of
Greenwich at 12 o'clock in
the afternoon.

On a meridian next to it,
it is an hour either earlier
or later.
All the West-European countries have
adapted themselves to the
Mid-European time (MET),
except for England and
Ireland of course,
they stick to the Greenwich Mean Time (GMT).
In the summer, a big number of
the countries has the summertime.
With the summertime an hour
is added, and the clock is
changed to an hour later.
The time is now the same as
the time that it should be
in the zone next to it.
(eastwards)

Since 1956 one distinguishes
UT0 the universal Time (UT )
or worldtime (WT)
as noticed in Greenwich (GMT);
UT1, corrected for poleheightmovements;
UT2 in which the influence of
the season depended rotation
movements are corrected.
There will stay some
irregularities in the earth
rotation
which are unpredictable.
To eliminate these as well,
one has introduced,
for astronomic purposes,
the 'efemeriden' time,
with an unit of length of the
tropic year,
which started at January zero
1900 at 12 o'clock
'efemeriden' time.
(= December 31st 1899
at 12 o'clock
'efemeriden' time =
12 o'clock GMT
at 4.5 seconds past
December 31st 1899.)

Day and night.

When the Earth is turning
around the sun in her course,
it keeps
getting a different corner
where the sun falls in.
Because the Earth also turns
around it's own axis you get
day and night.
If the sun comes in front
of the earth from the right
like in the picture above,
then the right side of
the earth is lighted.
It is day there.
The Earth turns and that
is how every part of
it comes in the light
and dark part once in
the 24 hours.

Summertime and wintertime.

The reason that the days
in the northern hemisphere
(in the summer) last longer
is that the time is set
forward one hour and because
the sun between
the Tropic of Cancer and
the Tropic of Capricorn
moves back and forth every year.
When it is summer, on
the northern hemisphere the
sun is on the highest
tropic and closer to the
northern hemisphere.
When it is summer here in the north,
it is the opposite in the south.
(winter)