1. Time Zones
Map: By TimeZonesBoy [CC BY-SA 3.0 ( or Public domain], via Wikimedia Commons

2. 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
Map: By TimeZonesBoy [CC BY-SA 3.0 ( or Public domain], via Wikimedia Commons

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
Pictured is a sundial – they were used to determine times in towns and cities across the world before standard times were adopted
Image: By Pearson Scott Foresman [Public domain], via Wikimedia Commons

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
Until the 1880s, most towns in the United States had their own local time, usually based on “high noon,” the time in the town when the sun was at the highest point in the sky
Table: "Comparative-time-table" by Dinsmore (1857) - Dinsmore’s American Railroad and Steam Navigation Guide and Route-Book.. Licensed under Public Domain via Wikimedia Commons -
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
The prime meridian was established at Greenwich, England since England was a major shipping country and already had several ships using a meridian at Greenwich and because there was a well-respected observatory in Greenwich at the time
Image:

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

7. Time Zones
Since there are 360° of longitude around the Earth and 24 time zones, each time zone is approximately 15° of longitude wide
Image: By Pearson Scott Foresman [Public domain], via Wikimedia Commons

8. Time Zones The prime meridian is at 0° longitude
The international date line, where new days begin, is at 180° longitude
Map: "TimeZones" by as seen on Licensed under Public Domain via Wikimedia Commons -

9. 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
Map: "TimeZones" by as seen on Licensed under Public Domain via Wikimedia Commons -

10. Russia’s different time zones
Some countries are so large that they span multiple time zones
Notable examples include:
The United States (6)
Russia (11)
Brazil (3)
Map: PlatonPskov [CC BY-SA 2.5 ( via Wikimedia Commons
Russia’s different time zones

11. Time Zones
Other large countries use single time zones that are larger than 15° of longitude
Notable examples include:
China
India
Map: "IST-CIA-TZ" by Nichalp, Ambuj.Saxena, Cpm0813 at en.wikipedia. - Source: en:Image:Timezones optimized.png Originally from en.wikipedia; description page is/was here.. Licensed under Public Domain via Wikimedia Commons -

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
One way many people remember how to adjust clocks during daylight savings time is by thinking of it as “spring” forward and “fall” back
Map: "DaylightSaving-World-Subdivisions" by Paul Eggert - based on Image:BlankMap-World-Subdivisions.PNG, plus the data in the tz database, plus data in the maps on the INMS's Time Zones & Daylight Saving Time page.. Licensed under CC BY-SA 3.0 via Wikimedia Commons -
Blue = currently uses DST, orange = once used DST but not currently, red = has not used DST

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
Map: "National-atlas-timezones-2006". Licensed under Public Domain via Wikimedia Commons -
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
Map: "TimeZones" by as seen on Licensed under Public Domain via Wikimedia Commons -

15. 3pm4pm 5pm  6pm Determining Times
As you move east, add one hour to your time for each time zone you move through, for example:
3pm4pm 5pm  6pm
Map: "National-atlas-timezones-2006". Licensed under Public Domain via Wikimedia Commons -

16. 10am11am12pm 1pm Determining Times
Conversely, as you move west, subtract one hour for each time zone, for example:
10am11am12pm 1pm
Map: "National-atlas-timezones-2006". Licensed under Public Domain via Wikimedia Commons -

17. Practice Questions
If it is 9am in California, what time is it in Colorado? (10am)
If it is 6pm in Iowa, what time is it in New York? (7pm)
If it is 3pm in Louisiana, what time is it in Maine? (4pm)
If it is noon in Georgia, what time is it in Arkansas? (11am)
If it is 6am in Ohio, what time is it in Wyoming? (4am)
If it is 10pm in Nevada, what time is it in Illinois? (12am/midnight)
If it is 2pm in Michigan, what time is it in Alabama (1pm)
If it is 8am in Montana, what time is it in South Carolina? (10am)
If it is midnight in West Virginia, what time is it in the state of Washington? (9pm)
If it is 11am in New Mexico, what time is it in Massachusetts? (1pm)
Most of Arizona does not use daylight savings time
Map: "National-atlas-timezones-2006". Licensed under Public Domain via Wikimedia Commons -