Four standard time zones for the continental U.S.A. were introduced in 1883.

Before 1883, over 300 local "sun times" were used to calculate time across the continental U.S. Each city had its own time standard based on the location of the sun. This system worked adequately until railroad travel became popular. Railroad travel enabled people to travel longer distances more quickly than ever before, and the many time differences began to create problems. Railway schedules were confusing when different rail lines used different time standards, and when trains needed to change the times on their schedules as they passed through different time zones. In response to the problem, U.S. railway managers agreed to stop using the local time zones. Instead, they would use four standardized time zones, Eastern, Central, Mountain and Pacific. After getting the cooperation of the cities the railroads passed through, the American Railway Association requested that the U.S. Naval Observatory, which kept the official time for the U.S, make the change to four time zones. At noon Greenwich Mean Time on this day in 1883, the U.S. Naval Observatory began broadcasting the new time, and people across the country reset their clocks and watches to match the time in their new time zone. Instantly, a hodgepodge system of local time zones was transformed into the simpler system that is still in use today.

Illuminations
In Grouchy Lessons of Time (Pre-K-2), part of the unit Magnificent Measurement (Pre-K-2),students learn the concept of time. The activities focus students' attention on the attributes of time and enable students at varying levels to develop knowledge and skills in telling time. Assessment tools in Microsoft Word and PDF (Adobe Acrobat) formats are also included.

ReadWriteThink
Students are introduced to time zones using the time zone map in their phone book in one of several activities in Teaching Language Skills Using the Phone Book (3-5).

Science NetLinks
Most people agree that time flies when you're having fun, but time also flies when you're taking an impossible math test. The Science Update Time Flies (6-12) examines a new study that may explain why.

EDSITEment
In I Hear the Locomotives: The Impact of the Transcontinental Railroad (3-5), students analyze archival material in order to make connections between the arrival of the railroads and many of the changes that occurred subsequently in the United States and its territories.