RAP• Given the following pie chart, explain ALL the

data. (You need to duplicate the pie graph in your ISN.)

Time Zones• With the advent of rapid travel by trains in the

19th century, it became necessary to standardize the time for all cities within a certain region.

• In November 1883, the railroad companies divided the continental United States into four time zones: Eastern, Central, Mountain, and Pacific.– Everyone in a time zone set their clocks to the same

standard time.

Time Zones• In 1884, an international conference was held

in Washington D.C. by 26 countries.– The world was divided into 24 time zones, with

each zone being roughly 15 degrees wide in longitude.

– Since there are 24 hours in a day, and 360/24=15, the time in each zone differs from the time in adjacent zones by one hour.

Time Zones• By international agreement, longitude is measured

from the prime meridian. • This meridian passes through the Royal Observatory

in Greenwich, England. • Time is measured from Greenwich, England and is

called Greenwich Mean Time (GMT)• For each time zone east of the prime meridian,

clocks must be set one hour ahead of GMT.• For time zones west of the prime meridian, clocks

are set one hour back from GMT.

Time Zones• Time zones do not follow meridians exactly;

political boundaries are often used to draw time zone lines.

• Times zones have been modified for political, social, and economic reasons.

Time Zones• International Date Line runs north-south

through the Pacific Ocean at 180 degrees. This time is 12 hours from GMT.

• There is a time difference of 24 hours between the two sides of the 180 degree meridian. It is called the International Date Line because when you cross it the date and day change.

Cross from east to west – gain a dayCross from west to east – lose a day

Time Zone Changes• Some countries have made changes. • For example, most of the US has daylight

savings time in the summer to have more evening hours of daylight.

A.M. and P.M.

• At midday, the Sun is on your meridian.– this occurs close to, or at noon.–A.M. comes from ante meridiem (before

midday)–P.M. comes from post meridiem (after

midday)

Time Zone Practice

• If it is 12:00 P.M. in the Central Time Zone, what time is it in the Pacific Time Zone?• If it is 7:00 P.M. in the Eastern Time Zone,

what time is it in the Mountain Time Zone?• If it is 7:44 A.M. in the Pacific Time Zone, what

time is it in the Central Time Zone?

WIOhttp://teachersites.schoolworld.com/webpages/NCouncil/

– Draw a rough map of the continental United States.– Divide the United States into the four continental time

zones.– Write and answer the following questions:1. If it is 1:00 P.M. in the Mountain Time Zone, what time

is it in the Eastern Time Zone?2. If it is 10:00 A.M. in the Pacific Time Zone, what time is

it in the Central Time Zone?3. If it is 4:00 A.M. in the Pacific Time Zone, what time is

it in the Eastern Time Zone?

Resources

• http://www.astro.virginia.edu/SST/resources/The%20Seasons.pdf