Time Zones

Many years ago before the current standardization. Individual towns and cities had their own means of determining time. Time could vary from one town to another by as much as 30 minutes or more. Which played havoc with time schedules.

Time zones were first used in 1883 by the railroads in order to standardize their schedules. The continental US was divided into four time zones with Noon being when the sun is highest in the sky. Later, to conserve energy and candles, Most states, with the exception Hawaii and most of Indiana and Arizona, go on daylight saving time (DST) from April until October.

GMT - Greenwich Mean Time

Originally, the local time at the Royal Greenwich Observatory in Greenwich, England was chosen as standard at the 1884 International Meridian Conference, leading to the widespread use of Greenwich Mean Time in order to set local clocks. This location was chosen because by 1884 two-thirds of all charts and maps already used it as their prime meridian.

The Greenwich Meridian (Prime Meridian or Longitude Zero degrees) marks the starting point of every time zone in the World. GMT is Greenwich Mean (or Meridian) Time is the mean or average time that the earth takes to rotate from noon-to-noon. Which is the astronomical basis for time.

The Meridian Line is an imaginary line which runs from the North Pole to the South Pole. By international convention it runs through "the primary transit" instrument which is the main telescope at the Royal Observatory in Greenwich. This also includes the line that runs 180° from Greenwich also known as the International Date Line. Which is on the opposite side of the world.

Greenwich Mean Time is the international or world time standard, which is the basis of the world time clock. GMT marks precision time and military time sometimes called Zulu Time.

Where is Greenwich, England?

Latitude 51° 28' 38"N (North of the Equator) Longitude 0° 0' 0" Located across the Themes River North of London, England. GMT remains the same all year around.

UTC - Coordinated Universal Time

UTC is not a true acronym; it is a variant of Universal Time, or UT, and has a modifier C (for "coordinated") appended to it just like other variants of UT. It is sometimes erroneously expanded into "Universal Time Code".

English speakers and French speakers each wanted the initials of their respective languages' terms to be used internationally: CUT for coordinated universal time and TUC for temps universel coordonné. As a compromise, a variation of the English term - with the verbal adjective trailing as in French - supplied the initials of the abbreviation: "universal time, coordinated" became UTC. In the U.S. it is said Coordinated Universal Time.

Coordinated Universal Time or UTC, also sometimes referred to as "Zulu Time" or "Z", is an atomic realization of Universal Time (UT) or Greenwich Mean Time (GMT). Time zones around the world are expressed as positive and negative offsets from UT. The Atomic clock is adjusted by using "Leap Seconds" because it is very linear and constant and the Earths rotation and orbit isn't.

The UT time zone is sometimes denoted by the letter Z since the equivalent nautical time zone (GMT) has been denoted by Z since about 1950, and by a "zone description" of zero hours since 1920. Since the NATO phonetic alphabet and radio-amateur word for Z is "Zulu", UT is sometimes known as Zulu time.

DST - Daylight Savings Time

The United States uses eight time zones. From east to west they are Atlantic Standard Time (AST), Eastern Standard Time (EST), Central Standard Time (CST), Mountain Standard Time (MST), Pacific Standard Time (PST), Alaskan Standard Time (AST), Hawaii-Aleutian Standard Time (HST), and Samoa Standard Time (UTC-11) for the American Samoan Island Group in the Pacific.

Currently, in the United States, Daylight Saving Time begins at 2:00 a.m. local time on the first Sunday in April. On the last Sunday in October areas on Daylight Saving Time return to Standard Time at 2:00 a.m.

In the United States, Under the Uniform Time Act, the Department of Transportation is in charge of time zones in the United States and ensuring that jurisdictions observing Daylight Saving Time begin and end on the same date.

On Monday August 8, 2005 President Bush signed into law a broad energy bill that will extend Daylight Saving Time by four weeks in 2007. The provisions of the bill call for Daylight Saving Time to begin three weeks earlier on the second Sunday in March and end one week later on the first Sunday in November. Currently Daylight Saving Time starts on the first Sunday in April and ends on the last Sunday in October.

In 2007 when the provisions take effect Daylight Saving Time will begin on March 11 and end on November 4, 2007. This change will become permanent and the added four weeks time will be observed every year in an effort to conserve energy.

While polls indicate most people favor extending Daylight Saving Time there are opponents who fought against the extension. The airline industry has said it will cost millions of dollars to change schedules and some school systems have concerns that students will be waiting for the bus in darkness in the mornings. It is expected that school systems will issue advisories to both parents and students on how to handle these situations.

There have been many proponents of extending Daylight Saving Time, including operators of golf courses, theme parks and businesses providing outdoor activities.

Pros

Energy Savings - will possibly save 100,000 barrels of oil daily. People will turn interior and exterior lights on later in the day which will save electricity. Lighting for evening sports events can be turned on one hour later.

Recreation Time - people will have more time to enjoy outdoor activities such as golf, tennis and theme parks.

Farming - many farmers work part time and will have an extra hour to work after they arrive home. Full time farmers may not benefit.

Cons

School Children - will possibly wait in the pitch dark for the school bus. Example, in Louisville, Kentucky sunrise will occur at 8:01 on March 11, 2007, however, Louisville schools currently begin classes at 7:40 for middle and high school.

Business - the airline industry claims it will cost millions of dollars to adjust schedules.

Computers, Clocks and Gadgets - many electronic devices automatically adjust for day light saving time. Some of these devices will show incorrect times. Some computer software will have to be rewritten or updated.

How To Convert To GMT, UTC, Zulu Time.

You first must convert local time from a 12 hour clock to a 24 hour clock. Then you must know what time zone you are in and how many hours that time zone is before or after Greenwich, England time.

We are in the Eastern Standard Time Zone which is UTC-5 or 5 hours behind Greenwich, England Time or GMT. In the conversion the minutes and seconds, if used, do not change. Only the hours.

For example: If you wanted to convert 6:43 am to Zulu Time for today's date. 6:43 am would be 0643 hours in the 24 hour clock. Then you would ADD 5 hours to calculate for Zulu Time or 1143Z hours today's date.

If you wanted to convert 9:27 pm to Zulu Time for today's date. 9:27 pm would be 2127 hours in the 24 hour clock. Then you would ADD 5 hours to calculate for Zulu Time or 0227Z hours tomorrows date.

The catch to all of this is that this works in the winter months when we are on Eastern Standard Time. When we are on Eastern Daylight Savings Time in the summer the UTC Zone changes because we move the clocks ahead one hour. So you would use UTC-4 hours instead of UTC-5 hours. Which means you would ADD 4 hours instead of 5 hours.