In order to keep track of the complexities of the world's time zones, most computer operating systems and software applications use one of the following two common data sources. You may not realize it, but this happens all over the world, dozens of times every year! Time Zones in Computing The reason more than one rule can exist is simple: Governments often change their minds! Whenever a government decides that their time zone should either move to a different base offset, enact or rescind daylight saving time, or change the transition dates of when daylight saving time begins or ends, the existing rule becomes invalid, and a new rule goes into effect. Time Zones of the Continental United States Time zones can change! Likewise, UTC-4 is associated with "Eastern Daylight Time" and abbreviated "EDT". For example, in the US Eastern Time zone, UTC-5 is associated with "Eastern Standard Time" and abbreviated "EST". The transition dates and times that daylight saving time starts and endsĮach offset within the rule will usually have an associate name and abbreviation. This is usually (but not always) one hour greater than the standard offset. One or more rules which consist of: The effective date and time for the rule A standard offset from UTC, such as UTC-5 If the time zone uses daylight saving time: The daylight offset, such as UTC-4.A legal name (or a common name), such as "Eastern Time".A geographic boundary that can usually be plotted on a map.Time Zone CharacteristicsĪ time zone consists of all of the following: Therefore, a time zone cannot be represented by just a single number. In fact, many time zones have two offsets - one that is followed during "standard time", and one that is followed during "daylight time" (which is sometimes called "summer time"). An offset is simply one characteristic of a time zone. Time Zone != OffsetĪ time zone is not just an offset from UTC or GMT. However, there are also time zones that are in place by convention, without any governing laws. Usually these rules are set by the laws of that region. Within the boundaries of a time zone, all local clocks should follow the same set of timekeeping rules. When talking about time zones, it's important to recognize that you are talking about a real place on the surface of the Earth. If you enjoy this topic, please consider watching the video course! A time zone is a geographic region This material is also covered in my Pluralsight course, Date and Time Fundamentals.
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