Official map of U.S. Time Zones, courtesy of NationalAtlas.gov.
Time zones are the dividing lines that make the days more uniform in the world according to daylight and night.
Without time zones, midnight would be dark in one part of the world while the sun would shine in another hemisphere. In the United States, there are six official time zones and one special time zone for the territory of Puerto Rico and the Virgin Islands. This blog post will focus on the United States’ time zones and delve more deeply into their locations and history.
According to the National Atlas, a website published by the U.S. Government, time zones in the United States, as well as Canada, were mandated on November 18, 1883 by the railroad companies. As mentioned in an earlier blog post by OnlineClock.net about time zones, American cities had used their own method of timing before this. They based their method on the position of the sun and solar time. Later in March of 1918, the use of Standard Time with time zones was introduced into the U.S. laws. The Interstate Commerce Commission, or ICC, had the task of deciding on the boundaries for each time zone. As seen on time zone maps, the distances are evenly spaced.
Soon after that, the United States Department of Transportation was given the authority to define boundaries. Official records of the time zone boundaries are outlined in the Code of Federal Regulations, Title 49- Transportation, Subtitle A, Office of the Secretary of Transportation, Part 71 – Standard Time Zone Boundaries. The United States Naval Observatory keeps current records of all time zones observed in the United States and outlying territories. The National Institute of Standards and Technology clarifies the reason why U.S. time zones’ edges appear crooked on maps. This is due to convenience and preferences of local populations that are along the boundaries. Using the U.S. Naval Observatory’s time zone coordinates, the official U.S. zones will each be explained in the following paragraphs.
Beginning from east to west, the first time zone uses Atlantic Standard Time, which is obtained by subtracting 4 hours from UTC, or Coordinated Universal Time. Also it may be listed as GMT-4, meaning four hours subtracted from Greenwich Mean Time. It is the 60th meridian west of the Greenwich Observatory. Included in this time zone are Puerto Rico and the U.S. Virgin Islands.
Eastern Standard Time Zone
The next time zone on the map is the Eastern Standard Zone. The offset from UTC is -5 hours, also written as GMT-5. As the 75th meridian west of the Greenwich Observatory, this zone includes several eastern states in the U.S. Seventeen states and the District of Columbia are part of this time zone. There are 6 states that are split between Central and Eastern time. The Eastern zone includes most of Florida, except the Panhandle area. Kentucky, Michigan and Tennessee are all split by Central and Eastern time. There are a few portions in Indiana that observe Central time, but most of it is in the Eastern Standard Zone. Alabama is a Central zone state, except for a few communities, according to the Decatur Daily’s online publication. These include Smiths Station, Phenix City, Valley and Lanett, which are part of Georgia’s Columbus metro area.
The following states are included wholly in the Eastern Standard Time Zone:
- Connecticut
- Delaware
- Georgia
- Maine
- Maryland
- Massachusetts
- New Hampshire
- New Jersey
- New York
- North Carolina
- Ohio
- Pennsylvania
- Rhode Island
- South Carolina
- Vermont
- Virginia
- West Virginia
Central Time Zone
The Central Standard Time Zone is defined as UTC-6 or GMT-6 and is the 90th meridian west of the Greenwich Observatory. As mentioned in the above paragraph, Alabama is officially in this zone, with a few communities being exceptions. Oklahoma is another state that has one exception that excludes it from being entirely a Central zone state. The community of Kenton in the Panhandle area is the only town that observes Mountain time. Several states are mostly in the Central zone, but also have significant parts that fall in the Mountain time zone. These states are Kansas, Nebraska, South Dakota and North Dakota. Texas has a few small counties that fall in the Mountain Standard Zone also. States which are wholly included in the Central Standard Time Zone are:
- Arkansas
- Illinois
- Iowa
- Louisiana
- Minnesota
- Mississippi
- Missouri
- Wisconsin
Mountain Standard Time Zone
Mountain Standard Time is GMT-7 or UTC-7 and is the 105th meridian west of the Greenwich Observatory. As with every other time zone, Daylight Savings is always one number off from the Standard reading. So for Mountain time, it would be UTC-6 during Daylight Savings. However, most of the state of Arizona does not observe Daylight Savings Time, so it is continually on MST. This means that during the summer, the time in Arizona is always concurrent with Pacific Standard Time. The area that does observe Daylight Savings is the Navajo Nation Reservation. We have already discussed the states that border with CST, but there are a few that are divided between Pacific time and MST. These states are Oregon, Idaho and Nevada. The states that are wholly MST include:
- Arizona
- Colorado
- Montana
- New Mexico
- Wyoming
- Utah
Pacific Standard Time Zone
The Pacific Standard Time Zone is the last time zone in the continuous part of the U.S. It is defined as GMT-8 or UTC-8 and is the 120th meridian west of the Greenwich Observatory. Since the coordinates of the time zone fall so far west in the United States, most of the states in this zone are partially covered by MST also. The only two states that are entirely in the PST zone are California and Washington.
Alaska Standard Time is defined as UTC-9 or GMT-9 and is the 135th meridian west of the Greenwich Observatory. Originally, Alaska’s time zone was called “Central Alaskan Standard Time,” or CAT. According to the 1918 40 Stat. 450 & 56 Stat. 9 of the United States Congress, Alaska was to be considered UTC-10, which made it two hours behind the PST zone, instead of one hour. In 1967, according to United States Time Notes, Alaska was put into the AHST zone, which was Alaska-Hawaii Standard Time, still measured at UTC-10. It wasn’t until 1983 that most of Alaska was moved into the new AST zone that measured UTC-9 instead of UTC-10. Today the Aleutian Islands of Alaska remain in the UTC-10 zone, along with Hawaii. According to Greenwich Mean Time’s website, any old legal records that refer to Yukon Standard Time in Canada must now be timed concurrent with AST, as both UTC deductions are equal.
The Hawaii-Aleutian Standard Time Zone, or HAST, is GMT-10 and is the 150th meridian west of the Greenwich Observatory. One interesting fact about Hawaii is that it does not observe Daylight Savings Time. This means that during the summer months, Hawaii is 3 hours behind the PST zone instead of 2. From 1900 until 1947, Hawaii used a measurement of GMT-10:30. Their zone is also shared with the Cook Islands, Tokelau and parts of French Polynesia.
Although they are not part of the United States’ time zones, the United States Naval Observatory also includes two additional time zones in the list of U.S & Outlying Territories zones. These are Chamorro Standard Time and Samoa Standard Time. Samoa Standard Time is calculated as UTC-11, while Chamorro Standard Time is calculated by UTC+10, making it have a significant time difference ahead of all other territories and the United States. When traveling through the U.S., it is helpful to know what areas observe certain time zones and adjust car clocks and watches accordingly. Most cell phones, thanks to GPS chips, will automatically update when crossing time zones. However, many phones must receive a text or call to update, so send a text message to yourself to get the correct time.
And whatever you do, while you’re traveling between time zones, don’t forget to update the time for your computer’s settings. Our Online Alarm Clocks always use the time settings from your own computer to automatically show you the correct time. So, when you’ve traveled to a new time zone, all you have to do is update your computer’s time settings for your new location, and the correct time for the new time zone will automatically be shown on OnlineClock.net ! If for whatever reason you’d prefer to display the time from where you’ve come from on Online Clock, no problem – just leave your computer set to the time zone where you’ve come from.
We hope you’ve enjoyed geeking out with us about time zones today and have even learned a new thing or two about this wonderful system we’ve developed for standardizing the time across the entire U.S. of A.
Until next time, Clock Fans, we’re zoning on out of here…
Related posts: