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What in the World are Time Zones?
Transcript of What in the World are Time Zones?
And why do we have them?
Mass transportation and telecommunication c
Using local solar time became confusing.
Every railroad stop was based on a different local time.
For example, in Britain, local time differed by as much as 20 minutes from London.
New England, 1853, two trains heading toward each other on the same track collided because the train guards each had a different time on their watch. 14 passengers died.
Many countries today use variations of the original time zones. For instance, the land area of China covers 5 time zones, but the country of China uses one time zone 8 hours before Greenwich. Other countries use half-hour zones. In some places time zone "lines" are moved to incorporate areas claimed by different countries or for convenience so that all of one country, state, city, etc. is in the same time zone.
The rotation of the earth on its axis causes day and night. As the earth rotates, some locations move away from the sun into night while others move toward the sun into day.
There are 24 time zones to correspond with 24 hours in a day. The 360 degrees of the earth divided by 24 hours = time zones of 15 degrees. Each zone is based on a central meridian and extends 7 1/2 degrees on each side.
Sunrise & sunset occur at different times due to rotation of the earth.
Sundials used to tell time into Middle Ages.
Mechanical clocks invented
Each city set own time based on sun
Travelers had to reset watch every new city
Sir Sanford Fleming, Canadian, came up with a world-wide system for keeping time in 1878.
Based on 24 hour day and 360 degrees of longitude.
International Prime Meridian Conference held in Washington, D.C. in 1884.
Selected Greenwich, England as 0 degrees longitude, Prime Meridian. 24 time zones established from Prime Meridian.
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