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Greenwich Mean Time (GMT) is the mean solar 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
A prime meridian is an arbitrary meridian in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian form a great circle. This great circle divides a spheroid, like Earth, into two hemispheres: the Eastern Hemisphere and the Western Hemisphere. For Earth's prime meridian, various conventions have been used or advocated in different regions throughout history. Earth's current international standard prime meridian is the IERS Reference Meridian. It is derived, but differs slightly, from the Greenwich Meridian, the previous standard.
The International Meridian Conference was a conference held in October 1884 in Washington, D.C., in the United States, to determine a prime meridian for international use. The conference was held at the request of U.S. President Chester A. Arthur. The subject to discuss was the choice of "a meridian to be employed as a common zero of longitude and standard of time reckoning throughout the world". It resulted in the recommendation of the Greenwich Meridian as the international standard for zero degrees longitude.
Indian Standard Time (IST), sometimes also called India Standard Time, is the time zone observed throughout 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.
In the United States, time is divided into nine standard time zones covering the states, territories and other US possessions, with most of the country observing daylight saving time (DST) for approximately the spring, summer, and fall months. The time zone boundaries and DST observance are regulated by the Department of Transportation, but no single map of those existed until the agency announced intentions to make one in September 2022. Official and highly precise timekeeping services (clocks) are provided by two federal agencies: the National Institute of Standards and Technology (NIST) ; and the United States Naval Observatory (USNO). The clocks run by these services are kept synchronized with each other as well as with those of other international timekeeping organizations.
In geography and geodesy, a meridian is the locus connecting points of equal longitude, which is the angle east or west of a given prime meridian. In other words, it is a line of longitude. The position of a point along the meridian is given by that longitude and its latitude, measured in angular degrees north or south of the Equator. On a Mercator projection or on a Gall-Peters projection, each meridian is perpendicular to all circles of latitude. A meridian is half of a great circle on Earth's surface. The length of a meridian on a modern ellipsoid model of Earth has been estimated as 20,003.93 km (12,429.87 mi).
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.
UTC+04:51 is an identifier for a time offset from UTC of +04:51.
Indian Standard Time (IST) is the time zone for Sri Lanka. It is 5 hours and 30 minutes ahead of GMT/UTC (UTC+05:30) as observed since 15 April 2006.
Madras Time was a time zone established in 1802 by John Goldingham, the first official astronomer of the British East India Company in India when he determined the longitude of Madras as 5 hours, 21 minutes and 14 seconds ahead of Greenwich Mean Time. It has been described as 8 minutes and 46 seconds from UTC+05:30 and 32 minutes and 6 seconds behind Calcutta Time which puts it at (UTC+05:21:14). Before India's independence, it was the closest precursor to Indian Standard Time which is derived from the location of the observatory at 82.5°E longitude in Shankargarh Allahabad in Uttar Pradesh.
Calcutta time was one of the two time zones established in British India in 1884. It was established during the International Meridian Conference held at Washington, D.C. in the United States. It was decided that India had two time zones: Calcutta would use the 90th meridian east and Bombay the 75th meridian east. It was determined as 5 hours, 53 minutes and 20 seconds ahead of Greenwich Mean Time (UTC+5:53:20).
The Republic of India uses only one time zone across the whole nation and all its territories, called Indian Standard Time (IST), which equates to UTC+05:30, i.e. five and a half hours ahead of Coordinated Universal Time (UTC). India does not currently observe daylight saving time.
Railway time was the standardised time arrangement first applied by the Great Western Railway in England in November 1840, the first recorded occasion when different local mean times were synchronised and a single standard time applied. The key goals behind introducing railway time were to overcome the confusion caused by having non-uniform local times in each town and station stop along the expanding railway network and to reduce the incidence of accidents and near misses, which were becoming more frequent as the number of train journeys increased.
Indigenous tribals have inhabited Mumbai (Bombay) since the Stone Age. The Kolis and Aagri were the earliest known settlers of the islands. The Maurya Empire gained control of the islands during the 3rd century BCE and transformed them into a centre of Hindu-Buddhist culture and religion. Later, between the 2nd century BCE and 10th century CE, the islands came under the control of successive indigenous dynasties: the Satavahanas, Abhiras, Vakatakas, Kalachuris, Konkan Mauryas, Chalukyas, Rashtrakutas, Silharas& Chollas.
Ireland uses Irish Standard Time in the summer months and Greenwich Mean Time in the winter period.
MoreSunlight or Project Moresunlight is a proposal to advance Indian Standard Time by 30 minutes. According to the proposal of MoreSunlight, the current time of India, which is +530 UTC should be advance to +600 UTC. The project is a conception of many government officers, elected representatives, members of the scientific community in India and civil society organizations and ordinary citizens.
Finland uses Eastern European Time (EET) during the winter as standard time and Eastern European Summer Time (EEST) during the summer as daylight saving time. EET is two hours ahead of coordinated universal time (UTC+02:00) and EEST is three hours ahead of coordinated universal time (UTC+03:00). Finland adopted EET on 30 April 1921, and has observed daylight saving time in its current alignment since 1981 by advancing the clock forward one hour at 03:00 EET on the last Sunday in March and back at 04:00 EET on the last Sunday in October, doing so an hour earlier for the first two years.
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
- ↑ "Indian Time Zones (IST)". Greenwich Mean Time (GMT). Archived from the original on 30 October 2006. Retrieved 13 August 2006.
- ↑ "Indian Time Zones (IST)". Project Gutenberg. International Conference Held at Washington for the Purpose of Fixing a Prime Meridian and a Universal Day. October, 1884 Protocols of the Proceedings. Retrieved 13 August 2006.
- ↑ "Bombay time". Mumbai-central.com. 8 December 2001. Archived from the original on 28 September 2007. Retrieved 13 August 2006.
- ↑ Doctor, Vikram (6 January 2010). "History of Bombay's quest for time". The Economic Times. Retrieved 1 January 2023.