Episode 8 (formerly 1508): Time Zones in the USA


The United States is a vast country. With its 50 states plus territories and commonwealths, some part of it occupies nine different time zones. To more effectively communicate with people in specific locations, it is helpful to understand time zones in general.

Coordinated Universal Time (UTC) is the 24-hour worldwide time standard system. UTC divides the globe into 24 equal zones based on longitude lines, or meridians. Meridians are imaginary lines drawn from the North Pole to the South Pole. The distance between each time zone meridian is 15 degrees of longitude, or 15 degrees of an imaginary circle drawn around the earth parallel to the equator.

The Prime Meridian, which runs through Greenwich in the United Kingdom, is considered point zero on the circle. Fifteen degrees in either direction constitutes a time zone. Each zone has a designated time that is one hour earlier than its adjacent zone to the east.

The area from the Prime Meridian to 15 degrees to the east is designated as UTC. The next time zone to the east is UTC +1 and so on. The time zone to the west of UTC is UTC -1, etc. The meridian where UTC +12 and UTC -12 meet is known as the International Date Line.

Note that the global time zone system is entirely arbitrary. People have agreed to use the system in order to communicate time consistently from place to place. However, in many places, the actual lines separating time zones do not accurately follow longitudinal lines, mainly because of political reasons. That is, countries and states can change the time zone borders however they wish, resulting in very irregular time zone borders.

Because UTC is a standardization system, not a naming convention, time zones have more common names. For example, UTC is also known as GMT (Greenwich Mean Time), UTC +1 is called CET (Central European Time), and so on. Furthermore, DST (Daylight Savings Time) is implemented in many places on Earth. Clocks are set one hour forward in the spring and one hour back in the fall, changing the time one hour on the clock.

The continental USA occupies four time zones in North America. The east coast falls under EST (Eastern Standard Time or UTC -5) for cities such as Miami, New York and Boston. One time zone to the west is CST (Central Standard Time or UTC -6), which has locations such as New Orleans, Dallas and Chicago.

People residing one more time zone further west live with MST (Mountain Standard Time or UTC -7), which contains Denver, Albuquerque and Salt Lake City. The West Coast, including Los Angeles, San Francisco and Seattle, uses PST (Pacific Standard Time or UTC -8).

In addition to the “lower 48”, Alaska designates its time zone as AKST (Alaska Standard Time), which is UTC -9. Hawaii uses HAST (Hawaii-Aleutian Standard Time), which is UTC -10.

The territories of American Samoa and the Midway and other islands use SST (Samoa Standard Time or UTC -11). The commonwealth of Puerto Rico and the territory of the US Virgin Islands enjoy AST (Atlantic Standard Time or UTC -4). The territories of Guam and the Northern Mariana Islands employ ChST (Chamorro Standard Time or UTC +10).

Not every place observes Daylight Savings Time (DST), but in places that do, the time zone acronym designation changes the S to D. For example, EST becomes EDT, and so on. The word “Savings” in the common name of the time zone becomes “Daylight”, as in “Eastern Daylight Time”. Nevertheless, the UTC designation does not change.

Practical reasons to know time zone differences come into play when telephoning someone in a different time zone. The same applies to doing business with people in faraway time zones. If you live near a time zone border meridian, you may need to know where your local TV station broadcasts from to determine what local time you can see the program. For this reason, many television stations specify two time zones. For example, the announcer might say, “See this show at 8:00 p.m. Eastern, 7:00 Central.”

It can be confusing to know which time zone a location is in and whether Daylight Savings Time is in effect. However, numerous websites on the Internet can tell you what time zone, UTC designation and local time pertains to any given location.

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One thought on “Episode 8 (formerly 1508): Time Zones in the USA

  1. Pingback: Episode 1609: United States Regions – Slow American English

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