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Greenwich Mean Time (GMT) is the local mean time at the Royal Observatory in Greenwich, London, counted from midnight. At different times in the past, it has been calculated in different ways, including being calculated from noon; as a consequence, it cannot be used to specify a particular time unless a context is given. The term "GMT" is also used as one of the names for the time zone UTC+00:00 and, in UK law, is the basis for civil time in the United Kingdom.
A time zone is an area which observes a uniform standard time for legal, commercial and social purposes. Time zones tend to follow the boundaries between countries and their subdivisions instead of strictly following longitude, because it is convenient for areas in frequent communication to keep the same time.
Universal Time is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle with respect to the International Celestial Reference Frame (ICRF), called the Earth Rotation Angle. UT1 is the same everywhere on Earth. UT1 is required to follow the relationship
Japan Standard Time, or Japan Central Standard Time, is the standard time zone in Japan, 9 hours ahead of UTC (UTC+09:00). Japan does not observe daylight saving time, though its introduction has been debated on several occasions. During World War II, the time zone was often referred to as Tokyo Standard Time.
The modern 24-hour clock is the convention of timekeeping in which the day runs from midnight to midnight and is divided into 24 hours. This is indicated by the hours passed since midnight, from 00(:00) to 23(:59), with 24(:00) as an option to indicate the end of the day. This system, as opposed to the 12-hour clock, is the most commonly used time notation in the world today, and is used by the international standard ISO 8601.
The Mountain Time Zone of North America keeps time by subtracting seven hours from Coordinated Universal Time (UTC) when standard time (UTC−07:00) is in effect, and by subtracting six hours during daylight saving time (UTC−06:00). The clock time in this zone is based on the mean solar time at the 105th meridian west of the Greenwich Observatory. In the United States, the exact specification for the location of time zones and the dividing lines between zones is set forth in the Code of Federal Regulations at 49 CFR 71.
Indian Standard Time (IST), sometimes also called India Standard Time, is the time zone observed throughout the Republic of India, with a time offset of UTC+05:30. India does not observe daylight saving time or other seasonal adjustments. In military and aviation time, IST is designated E* ("Echo-Star"). It is indicated as Asia/Kolkata in the IANA time zone database.
The Alaska Time Zone observes standard time by subtracting nine hours from Coordinated Universal Time (UTC−09:00). During daylight saving time its time offset is eight hours (UTC−08:00). The clock time in this zone is based on mean solar time at the 135th meridian west of the Greenwich Observatory.
Central European Time (CET) is a standard time of Central, and parts of Western Europe, which is one hour ahead of Coordinated Universal Time (UTC). The time offset from UTC can be written as UTC+01:00. It is used in most parts of Europe and in a few North African countries. CET is also known as Middle European Time and by colloquial names such as Amsterdam Time, Berlin Time, Brussels Time, Budapest Time, Madrid Time, Paris Time, Rome Time, Prague time, Warsaw Time or Romance Standard Time (RST).
Standard time is the synchronization of clocks within a geographical region to a single time standard, rather than a local mean time standard. Generally, standard time agrees with the local mean time at some meridian that passes through the region, often near the centre of the region. Historically, standard time was established during the 19th century to aid weather forecasting and train travel. Applied globally in the 20th century, the geographical regions became time zones. The standard time in each time zone has come to be defined as an offset from Universal Time. A further offset is applied for part of the year in regions with daylight saving time.
Hong Kong Time is the time in Hong Kong, observed at UTC+08:00 all year round. The Hong Kong Observatory is the official timekeeper of the Hong Kong Time. It is indicated as Asia/Hong_Kong in the IANA time zone database.
The Newfoundland Time Zone (NT) is a geographic region that keeps time by subtracting 3.5 hours from Coordinated Universal Time (UTC) during standard time, resulting in UTC−03:30; or subtracting 2.5 hours during daylight saving time. The clock time in this zone is based on the mean solar time of the meridian 52 degrees and 30 arcminutes west of the Greenwich Observatory. It is observed solely in the Canadian province of Newfoundland and Labrador. The Newfoundland Time Zone is the only active time zone with a half-hour offset from UTC in the Americas.
UTC+07:00 is an identifier for a time offset from UTC of +07:00. In ISO 8601 the associated time would be written as 2024-06-11T23:05:58+07:00. It is 7 hours ahead of UTC, meaning that when the time in UTC areas is midnight (00:00), the time in UTC+07:00 areas would be 7:00 in the morning.
The time in China follows a single standard time offset of UTC+08:00 based on the National Time Service Center of Chinese Academy of Sciences located in Mount Li, Lintong District, Xi'an City, Shaanxi Province, even though the country spans five geographical time zones. The official national standard time is called Beijing Time domestically because it is based on the 120th meridian east, where Beijing City is located, and China Standard Time (CST) internationally. Daylight saving time has not been observed since 1991. China Standard Time (UTC+8) is consistent across Mainland China, Hong Kong, Macau, Taiwan, as well as equivalent with Philippines, Singapore, Brunei, most of Mongolia, Malaysia, Irkutsk Time (Russia), Western Australia and Central Indonesia.
Malaysian Standard Time or Malaysian Time (MYT) is the standard time used in Malaysia. It is 8 hours ahead of Coordinated Universal Time (UTC). Malaysia does not observe daylight saving time.
The Chamorro Time Zone, formerly the Guam Time Zone, is a United States time zone which observes standard time ten hours ahead of Coordinated Universal Time (UTC+10:00). The clock time in this zone is based on the mean solar time of the 150th meridian east of the Greenwich Observatory.
Ireland uses Irish Standard Time in the summer months and Greenwich Mean Time in the winter period.
Cambodia follows UTC+07:00, which is 7 hours ahead of UTC. The local mean time in Phnom Penh was originally UTC+7:19. Cambodia used this local mean time until 1920, when it changed to Indochina Time, UTC+07:00; ICT is used all year round as Cambodia does not observe daylight saving time. Cambodia shares the same time zone with Western Indonesia, Thailand, Vietnam, Christmas Island, and Laos.
Reunified Vietnam follows Indochina Time (ICT), which is seven hours ahead of UTC, ICT is used all year round as Vietnam does not observe daylight saving time. Vietnam shares the same time zone with Thailand, Cambodia, Christmas Island, Laos, and Western Indonesia.
Nigeria observes West Africa Time (WAT), which is one hour ahead of Coordinated Universal Time (UTC+01:00), year-round as standard time. Nigeria has never observed daylight saving time. It shares WAT with fourteen other countries in Africa. Nigeria's local mean time was UTC+00:13:35.
References
- ↑ "Time Zone & Clock Changes in Bangkok, Thailand". www.timeanddate.com. Retrieved 2021-02-20.
- ↑ Arnold, Wayne (28 July 2001). "Thailand's Leader Wants to Switch Time Zones". The New York Times . Retrieved 2 July 2019.
- ↑ Mok Ly Yng. "What time is it really?". Mathematics Department, National University of Singapore. Retrieved 2 July 2019.
- ↑ "พระราชกฤษฏีกาให้ใช้เวลาอัตรา" (PDF). Royal Thai Government Gazette (in Thai). Archived from the original (PDF) on June 3, 2020. Retrieved 4 June 2020.
