1. BY:
Muhammad Sajjad (907)
Ph# +923346544625

2.  Time Zone
• Introduction
• History
 World Time Zones
 International data line (IDL)
• Introduction
• History
• Location
 How IDL Works

3.  Any region of the globe throughout which the
same standard time is used, is called time
zone.

4.  Before 1972, all time zones were specified as an offset
from Greenwich Mean Time (GMT), which was the mean
solar time at the meridian passing through the Royal
Observatory in Greenwich, London.
 In January 1972, however, the length of the second in both
Greenwich Mean Time and atomic time was equalized.
 Today, many countries operate on variations of the time zones
proposed by Sir Fleming.
 All of China (which should span five time zones) uses a single
time zone.
 Australia uses three time zones - its central time zone is a
half-hour ahead of its designated time zone.

5.  Before the invention of clocks, people marked the time of day
with apparent solar time.
For Example, the time on a sundial – which was typically different for
every settlement.
 The concept of standard time was adopted in the late 19th century .
 Sir Sandford Fleming outlined a plan for worldwide standard time in the
late 1870s.
 He recommended that the world be divided into twenty-four time zones,
each spaced 15 degrees of longitude apart.
 The present system employs 24 standard meridians of longitude (lines
running from the North Pole to the South, at right angles to the Equator)
15º apart, starting with the prime meridian through Greenwich, England.

6.  There are 25 integer World Time Zones from -12 through 0 (GMT) to
+12. Each one is 15° of Longitude as measured East and West from the
Prime Meridian of the World at Greenwich, England. Some countries
have adopted non-standard time zones, usually 30 minutes offset which
have a * designation.

8.  GMT is an absolute time reference and does not change with the seasons.
 London time is the same as Greenwich Mean Time less than half of the
year.
 GMT was established in 1884 at the International Meridian Conference,
when it was decided to the place the Prime Meridian at Greenwich,
England.

9.  The International Date Line is an imaginary line which runs
from the North Pole to the South Pole and is 180° away from
the Greenwich Meridian.

10.  While the world is divided into 24 time zones
 There has to be a place where there is a difference in
days
 There should be a place where the day truly "starts" on
the planet.
 Thus, the 180° line of longitude, exactly one-half way
around the planet from Greenwich, England and 0°
longitude is approximately where the International Date
Line is located.

11.  The International Conference in 1884 deemed that there would be a single
Universal Day and that this would begin at mean midnight at Greenwich.
 Twenty five time zones were established to the east and west of
Greenwich with the International Date Line lying along the 180° line of
longitude. The line deviates in places to avoid crossing any land. Along
this line the calendar moves into a new day but only in local time, which is
measured relative to Greenwich Mean Time.
 The earliest recommendations issued referring to the date line appear to
date from 1899 and 1900
 Two adjustments of the date line took place in 1910 near the island chain
of Hawaii and between Samoa and the Chatham Islands

12.  Philippines
 1844
 Alaska
 18 October 1867
 Samoan Islands and
Tokelau
 4 July 1892

13. •Over the years, the position of the International Date Line has changed
several times. Until 1845, the Philippines were on the eastern side of it. When
the United States bought Alaska in 1867 the line was moved to the west of it.
•The most recent change in the line was in 1995 when Kiribati moved a large
segment of it to the east, so that the entire nation would be on the same side of
the International Date Line.

14.  Let's say you fly from the United States to Japan. Let's suppose you leave
the United States on Tuesday morning. Since you're traveling west the
time advances slowly thanks to time zones and the speed at which your
airplane flies, but once you cross the International Date Line, it's suddenly
Wednesday.
 On the reverse trip home you fly from Japan to the United States. You
leave Japan on Monday morning but as you cross the Pacific Ocean, the
day gets later quickly as you cross time zones moving eastward in an
airplace. However, once you cross the International Date Line, the day
changes to Sunday.

15.  http://wwp.greenwichmeantime.com/info/time-zones-history.htm
 http://geography.about.com/od/physicalgeography/a/timezones.htm
 http://wwp.greenwichmeridian.com/date-line.htm
 http://geography.about.com/od/physicalgeography/a/idl.htm
 http://www.worldatlas.com/aatlas/infopage/dateline.htm
 http://aa.usno.navy.mil/faq/docs/international_date.php
 http://www.fao.org/fileadmin/templates/wfd2007/images/GMT_timezone-1.jpg