Time Zones What is a Time Zone A

Time Zones

What is a Time Zone? • A time zone is a region that has a standard time throughout it • There are 24 times zones throughout the world

Why do We Need Standard Time? • Before the late 1800 s, towns and cities would set their own times based on the sun • Due to the Earth’s rotation, each location’s time was different

Why do We Need Standard Time? • When railroads and telecommunications began to improve, it became difficult for each location to have its own time Table showing different times across the U. S. in 1857

Time Zones • In 1884, the international standard time system was established • The prime meridian was also established passing through Greenwich, England at 0° longitude

Time Zones • By the year 1900, almost everywhere on Earth used some form of standard time

Time Zones • Since there are 360° of longitude around the Earth and 24 time zones, each time zone is approximately 15° of longitude wide

Time Zones • The prime meridian is at 0° longitude • The international date line, where new days begin, is at 180° longitude

Time Zones • Time zone boundaries are irregular primarily due to political reasons – often it is helpful for a country to be completely within one time zone

Time Zones • Some countries are so large that they span multiple time zones • Notable examples include: – The United States (6) – Russia (11) – Brazil (3) Russia’s different time zones

Time Zones • Other large countries use single time zones that are larger than 15° of longitude • Notable examples include: – China – India

Time Zones • Many countries use daylight savings time (DST) during part of the year • Typically during DST, clocks are advanced one hour forward in the spring and adjusted back one hour in the fall Blue = currently uses DST, orange = once used DST but not currently, red = has not used DST

Time Zones • There are six time zones in the United States • Four time zones are in the continental United States: – Eastern – Central – Mountain – Pacific • The other two time zones are: – Alaska time – Hawaii time

Determining Times • If you know your local time, you can determine what time it is across the world

Determining Times • As you move east, add one hour to your time for each time zone you move through, for example: 3 pm 4 pm 5 pm 6 pm

Determining Times • Conversely, as you move west, subtract one hour for each time zone, for example: 10 am 11 am 12 pm 1 pm

Practice Questions