1. Time Zones

2. What is a Time Zone?

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

4. 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

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

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

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

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

9. 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

10. Some countries are so large that they span multiple time zones Notable examples include: – The United States – Russia – Brazil Russia’s different time zones

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

12. 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

13. 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

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