Time in Various Cities
Source: DaysPedia.Com
GMT - UTC - ZULU
Greenwich Mean Time (GMT) is the clock time at the Prime Meridian (0 degrees longitude) in Greenwich, England. Here, the word "mean" means "average." It refers to the fact that noon GMT is the moment on average each year when the sun is at its highest point in the sky at the Greenwich meridian. (Because of Earth's uneven speed in its elliptical orbit and it's axial tilt, noon GMT isn't always when the sun crosses the Greenwich meridian.)
For astronomical purposes, the GMT day was said to start at noon and run until noon the following day. For everyone else, the GMT day started at midnight. When everyone switched to the midnight-based convention in the 1920s and 1930s, this midnight-based time standard was given the new name of Universal Time. Since this change, the term GMT isn't used much anymore, except by those living in the UK and its Commonwealth countries where it's used to describe the local time during the winter months.
Coordinated Universal Time is a modern version of Greenwich Mean Time. One of the biggest differences between GMT and UTC is that UTC does not observe Daylight Savings Time. Another name for UTC Time is "Zulu" (sometimes called miliary time, or "Z Time.")
The abbreviation for Coordinated Universal Time is UTC which represents a compromise between the English (Coordinated Universal Time) and the French phrase - Temps Universel Coordonne.
London observes daylight savings time called BST (British Summer Time) which is 1 hour ahead of UTC (Coordinated Universal Time). During the winter, GMT - Greenwich Mean Time(UTC+0) is in use. In the UK, the clocks go forward 1 hour at 1am on the last Sunday in March, and back 1 hour at 2am on the last Sunday in October. The period when the clocks are 1 hour ahead is called British Summer Time. There’s more daylight in the evenings and less in the mornings (sometimes called Daylight Saving Time). When the clocks go back, the UK is on Greenwich Mean Time.
For comparison, below is the current time in Coordinated Universal Time (UTC) and the current time in London.
Coordinated Universal Time (UTC)
Current Time in London UK
The United States' Time Zone History
The US was divided into 4 standard time zones on November 18, 1883, and jurisdiction for the zones was given to the Interstate Commerce Commission (ICC). Since 1967, the US Department of Transportation (DOT) has been responsible for governing time zones in the country.
Time zones in the USA are defined in the U.S. Code, Title 15, Chapter 6, Subchapter IX - Standard Time. The time zones in the law are defined by their offset from Coordinated Universal Time (UTC).
There are 9 official time zones according to the law. In addition the uninhabited atolls of Baker Island (AoE) and Wake Island (WAKT) add to the time zone count, making 11 the total number of time zones in the US.
Almost all states in the US use Daylight Saving Time (DST). Most of Arizona and Hawaii do not use DST.