In The Sun Shows the Way you saw that the Sun rises in the east. Morning reaches the East Coast first, then moves west across the country. That is why clocks are set differently in different places.
Key idea
The 50 states use six time zones. From east to west: Eastern, Central, Mountain, Pacific, Alaska and Hawaii-Aleutian. Each zone is one hour earlier than the zone to its east.
Why it works
Why zones? Long ago, every town set its clocks by its own noon, when the Sun was highest. Towns a few miles apart had slightly different times, which made train schedules a mess. In 1883 the railroads agreed on a few standard zones, each about one hour of the Sun's motion wide, and later the law made them official. Everyone in a zone shares one clock time.
Worked example: Noon in New York
It is 12:00 noon in New York. What time is it in Los Angeles?
- New York is in the Eastern zone; Los Angeles is in the Pacific zone.
- Going west: Eastern to Central to Mountain to Pacific is 3 zones.
- West is earlier, so subtract 3 hours: 9:00 a.m.
Answer: 9:00 a.m.
Common mistake
It is easy to think the West is "later." It is the other way around. The Sun rises in the East first, so Eastern clocks are ahead. When New Yorkers eat lunch, people in California are just starting their morning. Also, some states are split: most of Texas is Central, but its far western corner (El Paso) uses Mountain Time.