Time zone in the context of Central Indonesian Time

In general, an imaginary line is usually any sort of geometric line (more generally, curves) that has only an abstract definition and does not physically exist. They are often used to properly identify places on a map.

Some outside geography do exist. A centerline is a nautical term for a line down the center of a vessel lengthwise.

Longitude (/ˈlɒndʒɪtjuːd/, AU and UK also /ˈlɒŋɡɪ-/) is a geographic coordinate that specifies the east-west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians are imaginary semicircular lines running from pole to pole that connect points with the same longitude. The prime meridian defines 0° longitude; by convention the International Reference Meridian for the Earth passes near the Royal Observatory in Greenwich, south-east London on the island of Great Britain. Positive longitudes are east of the prime meridian, and negative ones are west.

Because of the Earth's rotation, there is a close connection between longitude and time measurement. Scientifically precise local time varies with longitude: a difference of 15° longitude corresponds to a one-hour difference in local time, due to the differing position in relation to the Sun. Comparing local time to an absolute measure of time allows longitude to be determined. Depending on the era, the absolute time might be obtained from a celestial event visible from both locations, such as a lunar eclipse, or from a time signal transmitted by telegraph or radio. The principle is straightforward, but in practice finding a reliable method of determining longitude took centuries and required the effort of some of the greatest scientific minds.

There are 11 time zones in Russia, which currently observe times ranging from UTC+02:00 to UTC+12:00. Daylight saving time (DST) has not been used in Russia since 26 October 2014. From 27 March 2011 to 26 October 2014, permanent DST was used.

Coordinated Universal Time or UTC is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communication, navigation, scientific research, and commerce.

UTC has been widely embraced by most countries and is the effective successor to Greenwich Mean Time (GMT) in everyday usage and common applications. In specialised domains such as scientific research, navigation, and timekeeping, other standards such as UT1 and International Atomic Time (TAI) are also used alongside UTC.

A calendar date is a reference to a particular day, represented within a calendar system, enabling a specific day to be unambiguously identified. Simple math can be performed between dates; commonly, the number of days between two dates may be calculated, e.g., "25 December 2025" is ten days after "15 December 2025". The date of a particular event depends on the time zone used to record it. For example, the air attack on Pearl Harbor that began at 7:48 a.m. local Hawaiian time (HST) on 7 December 1941 is recorded equally as having happened on 8 December at 3:18 a.m. Japan Standard Time (JST).

A particular day may be assigned a different nominal date according to the calendar used. The de facto standard for recording dates worldwide is the Gregorian calendar, the world's most widely used civil calendar. Many cultures use religious calendars such as the Gregorian (Western Christendom, AD), the Julian calendar (Eastern Christendom, AD), Hebrew calendar (Judaism, AM), the Hijri calendars (Islam, AH), or any other of the many calendars used around the world. Regnal calendars (that record a date in terms of years since the beginning of the monarch's reign) are also used in some places, for particular purposes.

In the Gregorian calendar, New Year's Eve refers to the evening, or commonly the entire day, of the last day of the year, 31 December, also known as Old Year's Day. In many countries, New Year's Eve is celebrated with dancing, eating, drinking, and watching or lighting fireworks. Many Christians attend a watchnight service to mark the occasion. New Year's Eve celebrations generally continue into New Year's Day, 1 January, past midnight.

The local time zone determines the advent of the New Year; the first places to welcome the New Year are west of the International Date Line: the Line Islands (part of Kiribati), Samoa and Tonga, in the Pacific Ocean. In contrast, American Samoa, Baker Island and Howland Island (part of the United States Minor Outlying Islands) are among the last.

Japan Standard Time (日本標準時, Nihon Hyōjunji; JST), or Japan Central Standard Time (中央標準時, Chūō Hyōjunji; JCST), 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.

Japan Standard Time is equivalent to Korean Standard Time, Pyongyang Time (North Korea), Eastern Indonesia Standard Time, East-Timorese Standard Time, Palau Time, and Yakutsk Time (Russia).

The Antarctic Convergence or Antarctic Polar Front is a marine belt encircling Antarctica, varying in latitude seasonally, where cold, northward-flowing Antarctic waters meet the relatively warmer waters of the sub-Antarctic. The line separates the clockwise Antarctic circumpolar current from other oceans. Antarctic waters predominantly sink beneath the warmer subantarctic waters, while associated zones of mixing and upwelling create a zone very high in marine productivity, especially for Antarctic krill.

This line, like the Arctic tree line, is a natural boundary rather than an artificial one, such as the borders of nations and time zones. It not only separates two hydrological regions, but also separates areas of distinctive marine life and climates.

The Maritimes, also called the Maritime provinces, is a region of Eastern Canada consisting of three provinces: New Brunswick, Nova Scotia, and Prince Edward Island. The Maritimes had a population of 1,899,324 in 2021, which makes up 5.1% of Canada's population. Together with Canada's easternmost province, Newfoundland and Labrador, the Maritime provinces make up the region of Atlantic Canada.

Located along the Atlantic coast, various aquatic sub-basins are located in the Maritimes, such as the Gulf of Maine and Gulf of St. Lawrence. The region is located northeast of New England in the United States, south and southeast of Quebec's Gaspé Peninsula, and southwest of the island of Newfoundland. The notion of a Maritime Union has been proposed at various times in Canada's history; the first discussions in 1864 at the Charlottetown Conference contributed to Canadian Confederation. This movement formed the larger Dominion of Canada. The Mi'kmaq, Wolastoqiyik and Passamaquoddy people are indigenous to the Maritimes, while Acadian and British settlements date to the 17th century. The Maritimes are within the Atlantic time zone, putting them one hour ahead of Quebec and the New England region of the United States.

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.

Because of Earth's uneven angular velocity in its elliptical orbit and its axial tilt, noon (12:00:00) GMT is rarely the exact moment the Sun crosses the Greenwich Meridian and reaches its highest point in the sky there. This event may occur up to 16 minutes before or after noon GMT, a discrepancy described by the equation of time. Noon GMT is the annual average (the arithmetic mean) moment of this event, which accounts for the word "mean" in "Greenwich Mean Time".

The Iranian calendars or Iranian chronologies (Persian: گاه‌شماری ایرانی, Gâh Šomâriye Irâni) are a succession of calendars created and used for over two millennia in Iran, also known as Persia. One of the longest chronological records in human history, the Iranian calendar has been modified many times for administrative purposes. The most influential person in laying the frameworks for the calendar and its precision was the 11th century Persian polymath, Omar Khayyam. The modern Iranian calendar is the Solar Hijri calendar, currently the official civil calendar in Iran.

Nowruz, the Iranian New Year, begins at the midnight nearest to the instant of the northern spring equinox, as determined by astronomic calculations for the meridian of Tehran (52.5°E). Thus the calendar is observation-based, unlike the Gregorian calendar, which is rule-based. This equinox occurs on or about 20 March of the Gregorian calendar. The time zone of Iran is Iran Standard Time, UTC+03:30.

In modern usage, civil time refers to statutory time as designated by civilian authorities. Modern civil time is generally national standard time in a time zone at a fixed offset from Coordinated Universal Time (UTC), possibly adjusted by daylight saving time during part of the year. UTC is calculated by reference to atomic clocks and was adopted in 1972. Older systems use telescope observations.

In traditional astronomical usage, civil time was mean solar time reckoned from midnight. Before 1925, the astronomical time 00:00:00 meant noon, twelve hours after the civil time 00:00:00 which meant midnight. HM Nautical Almanac Office in the United Kingdom used Greenwich Mean Time (GMT) for both conventions, leading to ambiguity, whereas the Nautical Almanac Office at the United States Naval Observatory used GMT for the pre-1925 convention and Greenwich Civil Time (GCT) for the post-1924 convention until 1952. In 1928, the International Astronomical Union introduced the term Universal Time for GMT beginning at midnight.

UTC+08:00 is an identifier for a time offset from UTC of +08:00.

It is the most populous time zone in the world, as well as a possible candidate for ASEAN Common Time, mainly due to China's large population, with an estimated population of 1.4 billion people.

The time in China follows a single standard time offset of UTC+08:00, where Beijing is located, even though the country spans five geographical time zones. It is the largest sovereign nation in the world that officially observes only one time zone.

The nationwide standardized time is named Beijing Time (BJT; Chinese: 北京时间) domestically and China Standard Time (CST) internationally. Daylight saving time has not been observed since 1991.

Kaliningrad Time (KALT; Russian: калининградское время, romanized: kaliningradskoye vremya) is the time zone two hours ahead of UTC (UTC+02:00) and one hour behind Moscow Time (MSK−1). It is used in Kaliningrad Oblast.

Until 2011, Kaliningrad Time was identical to Eastern European Time (UTC+02:00; UTC+03:00 with daylight saving time). On 27 March 2011, Russia moved to permanent DST, switching Kaliningrad time permanently to UTC+03:00. On 26 October 2014, this law was reversed but daylight saving time was not reintroduced, so Kaliningrad is now permanently set to UTC+02:00.

Moscow Time (MSK; Russian: моско́вское вре́мя, romanized: moskovskoye vremya) is the time zone for the city of Moscow, Russia, and most of western Russia, including Saint Petersburg. It is the second-westernmost of the eleven time zones of Russia, after the non-continguous Kaliningrad enclave. It has been set to UTC+03:00 without DST since 26 October 2014; before that date it had been set to UTC+04:00 year-round on 27 March 2011.

Moscow Time is used to schedule trains (until 1 August 2018), ships, etc. throughout Russia, but air transport in Russia is scheduled using local time. Since 1 August 2018, Russian railways switched to using local time. Time in Russia is often announced throughout the country's other timezones on radio stations as Moscow Time, which is also registered in telegrams, etc. Descriptions of time zones in Russia are often based on Moscow Time rather than UTC; for example, Yakutsk (UTC+09:00) is said to be MSK+6 in Russia.

Samara Time (SAMT) is the time zone four hours ahead of UTC (UTC+4) and 1 hour ahead of Moscow Time (MSK+1). Samara Time is used in Astrakhan Oblast, Samara Oblast, Saratov Oblast, Udmurtia, and Ulyanovsk Oblast.