what is the time difference between utc and gmt
Coordinated Universal Time For most common and legal-trade purposes, the fractional second difference between UTC and UT (GMT) is inconsequentially small. Greenwich Mean Time is the legal standard in Britain during the winter, and this notation is familiar to and used by the population.[21]
Time in the United Kingdom The United Kingdom uses Greenwich Mean Time or Western European Time (UTC) and British Summer Time or Western European Summer Time (UTC+01:00).
Coordinated Universal Time The time zone using UTC is sometimes denoted UTC±00:00 or by the letter Z—a reference to the equivalent nautical time zone (GMT), which has been denoted by a Z since about 1950. Time zones were identified by successive letters of the alphabet and the Greenwich time zone was marked by a Z as it was the point of origin. The letter also refers to the "zone description" of zero hours, which has been used since 1920 (see time zone history). Since the NATO phonetic alphabet word for Z is "Zulu", UTC is sometimes known as "Zulu time". This is especially true in aviation, where "Zulu" is the universal standard.[24] This ensures all pilots regardless of location are using the same 24-hour clock, thus avoiding confusion when flying between time zones.[25] See the list of military time zones for letters used in addition to Z in qualifying time zones other than Greenwich.
Daylight saving time The dates on which clocks are to be shifted also vary with location and year, consequently, the time differences between regions also vary throughout the year. For example, Central European Time is usually six hours behind North American Eastern Time, except for a few weeks in March and October/November, while the United Kingdom and mainland Chile could be five hours apart during the northern summer, three hours during the southern summer, and four hours a few weeks per year. Since 1996, European Summer Time has been observed from the last Sunday in March to the last Sunday in October; previously the rules were not uniform across the European Union.[41] Starting in 2007, most of the United States and Canada observe DST from the second Sunday in March to the first Sunday in November, almost two-thirds of the year.[42] Moreover, the beginning and ending dates are roughly reversed between the northern and southern hemispheres because spring and autumn are displaced six months. For example, mainland Chile observes DST from the second Saturday in October to the second Saturday in March, with transitions at 24:00 local time.[43] In some countries time is governed by regional jurisdictions within the country so that some jurisdictions shift and others do not; this is currently the case in Australia, Brazil, Canada, Mexico, and the United States.[44][45]
Colon (punctuation) Syntactical-descriptive colons may separate the numbers indicating hours, minutes, and seconds in abbreviated measures of time.[5]
12-hour clock The American Heritage Dictionary of the English Language states "By convention, 12 AM denotes midnight and 12 PM denotes noon. Because of the potential for confusion, it is advisable to use 12 noon and 12 midnight."[22]