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Time Zones
•in early days everyone set their clocks
according to the sun - it was noon (12:00
p.m.) when the sun was at its highest point
(its "zenith") in the sky
•in larger communities, the military often
would fire off a gun to signal this
occurrence and everyone would reset their
watches; or, they would listen for the
tolling of the clock in town hall
•because the length of daylight changes,
this would not be exactly 24 hours, from
noon to noon
•as commerce developed and railways and
then telegraph communication became
more widespread, this use of solar time
became very difficult as each town would
have a slightly different solar time
(because the sun is not overhead all
places at the same time)
•conductors on trains often had
ludicrously complicated jobs, trying to
keep track of the correct time in various
small communities as they tried to keep
the trains running on time
•in 1886 the international community
adopted a series of measures that solved
this and other vexing navigational
problems at a huge conference in Berlin
(this was when all of Europe was at peace
- a rare occurrence - an international
agreement could be possible)
•a Canadian, Sir Sandford Fleming, had
devised the notion that became known as
"standard time", which depended on a
consistent system of latitude and
longitude
•latitude was easy - the equator was 00
and math determined the rest - but
where is the 00 line for longitude - it
could go anywhere and different
countries thought it should be through
their country
•in 1886 the world agreed that it should
pass through Greenwich, England (outside
London) as this was where a very
important observatory was located - This
line was called the Prime (or "first")
Meridian of longitude
•it was further agreed that the world
would be divided into 24 equal time zones
•since the earth is relatively round, there
would be 3600 of longitude
and therefore each time zone would be 150
wide (360/24 = 15)
•in each of these time zones everyone
would adopt the same time and as you
crossed from one time zone to another you
changed your watch by one full hour
Time Zones
Time Zones
•this was a huge improvement on the old
system and it was quickly adopted
•the agreement also allowed for nations to
alter the borders of each time zone
somewhat so that places that have a lot to
do with one another could be in the same
time zone for convenience sake
•there were some other variations as well,
eg. Newfoundland time
The International Dateline
If I could travel around the earth (to the
east) in an instant I would cross 24 time
zones. Each time I would cross a time
zone I would move my clock up one hour.
When I get back to where I started I
would be one DAY ahead of everyone else!
This happened to a famous explorer by the
name of Ferdinand Magellan. In order to
correct this problem The International
Dateline was created. It is an imaginary line
that simply tells travelers to adjust their
calendars. If you are traveling east and
cross the dateline you go back one day. The
dateline is the 180 degree line of longitude,
directly opposite the Prime Meridian.
Monday
Sunday
The End!