In the United States, time is divided into nine standard time zones covering the states, territories, and other US possessions, with most of the country observing daylight saving time (DST) during the spring, summer, and fall months. The time zone boundaries and DST observance are regulated by the Department of Transportation, and highly precise timekeeping services (clocks) are provided by two federal agencies: the National Institute of Standards and Technology (NIST) operating WWV radio, and the United States Naval Observatory (USNO). The clocks run by these services are kept synchronized with each other as well as with those of other international timekeeping organizations.
USA Time Zones
Here’s why we have different time zones:
1. Earth’s Rotation: As the Earth rotates, different regions enter and exit daylight at varying times. To account for this, we divide the world into time zones.
2. Historical Complexity: In the past, every US city used its own local time standard, resulting in over 300 local sun times. Time zones were a compromise, balancing geographic variations while still approximating mean solar time.
3. Scientific Basis: Earth completes one full rotation (360 degrees) in approximately 24 hours. Each hour corresponds to about 15 degrees of rotation, forming the basis for assigning time zones.
4. Economical Reasons: Farming, manufacturing, and other industries profit from DST with safer and longer daylight hours.
The four main U.S. time zones are: Eastern Time Zone, Central Time Zone, Mountain Time Zone, & Pacific Time Zone plus Alaska and Hawaii have their own unique time zones.
Originally DST ran from the last Sunday in April until the last Sunday in October. Two subsequent amendments, in 1986 and in 2005 have shifted these days so that daylight saving time now runs from the second Sunday in March until the first Sunday in November. This is another great technology beneficial to humanity. Bob Larson is a technologist and marketing director for 50 Plus.