We look at a clock and see a precise time, then open a calendar and accept that the year is 1975, 1999, 2026 or else. Behind these apparently ordinary actions lies a complex international system developed over centuries through scientific discoveries, political decisions, economic interests and cultural traditions. Time is measured with atomic precision (but not in everyday life), although the way we convert it into local time, a date and a calendar year still depends on decisions made by individual states and societies.
This explains why two places at similar longitudes may use different local times, while two countries existing at exactly the same moment may record different years – these decisions may be extremely related to politics, historical events or just misunderstandings.
What is metrology?
Metrology is the science of measurement and its application. Its name comes from the Greek words metron, meaning “measure”, and logos, meaning “study” or “science”. It covers the definition of units in all fields or topics, the development of measurement methods, the comparison of results, and the assessment of accuracy and uncertainty. Without shared units and traceable standards, results obtained in different laboratories, countries and historical periods would be difficult to compare.
International cooperation in modern metrology developed particularly rapidly after the Metre Convention was signed in 1875. The convention created a framework through which countries could establish and maintain a common system of measurement. The International Bureau of Weights and Measures, known by its French abbreviation BIPM, now coordinates the International System of Units (SI) and contributes to the production of the world’s reference time scale (1).
Time is one of the base quantities in the SI, and its unit is the second. The modern definition of the second is based on the frequency of a particular transition in the caesium-133 atom. This allows time to be measured far more consistently than would be possible by observing the Earth’s rotation alone. International Atomic Time (TAI) is calculated using data from many atomic clocks maintained by national metrology institutes and specialised laboratories around the world.
Coordinated Universal Time (UTC), the principal international time scale, is derived from this system. UTC retains the uniformity of atomic time and has historically been adjusted with leap seconds so that it remains approximately aligned with time derived from the Earth’s rotation (2). The time we use today therefore brings together two different systems: exceptionally stable atomic clocks and the slightly irregular motion of our planet. It is worth mentioning that our planet is moving accross the Universe, has many different types of rotations and as many other thing in nature is not ideal.
Metrology explains how the duration of the second can be measured and reproduced anywhere in the world. Dividing the day into local times also requires geography, astronomy and political decisions, which sometimes can be quite illogical.
How one meridian became a global standard
Before standard time was introduced, towns and cities generally kept their own local solar time. Noon occurred when the Sun reached its highest point above the local horizon. Since the Earth rotates through 360 degrees in approximately 24 hours, a difference of one degree of longitude corresponds to about four minutes of local solar time.
Time Zones of the World
Explore official UTC offsets and compare how time-zone boundaries follow political borders, territories and regional connections.
While people travelled relatively slowly, these differences rarely caused serious practical problems. The expansion of rail transport, telegraphy, international shipping and global trade during the nineteenth century changed the situation. Timetables and communications began to require a common time, while navigation and cartography needed a single reference line from which longitude could be measured.
The problem also had a political dimension. No prime meridian exists as a naturally privileged line. The Equator is defined by the physical geometry of the Earth as a celestial body, while a zero meridian can be drawn through any chosen point. At different times, maps used meridians passing through Ferro, Rome, Copenhagen, Washington, Paris and Greenwich. Selecting one of them meant granting international recognition to a particular national scientific infrastructure and cartographic tradition.
The rivalry between the Greenwich and Paris meridians was especially strong. The Paris Observatory was founded in the seventeenth century, and its meridian served French cartography for a long period. The Royal Observatory at Greenwich also developed an extensive astronomical and navigational tradition, closely connected with the maritime power of the British Empire.
In 1884, representatives of 25 countries met in Washington, D.C., for the International Meridian Conference. By 22 votes to one, with France and Brazil abstaining, the conference recommended that the meridian passing through the transit instrument at the Greenwich Observatory should be adopted as the common prime meridian (3). The British proposal had a considerable practical advantage: nearly two thirds of the world’s shipping tonnage already used charts based on Greenwich. Replacing this system would have involved far greater expense and created a risk of navigational confusion (4).
The French delegation defended the idea of a “neutral” meridian that would not pass through the territory of a major state. Behind the scientific arguments were questions of national prestige, influence and competition between two leading European powers. France continued to use Paris time until 1911, when it legally adopted Greenwich time, although the law described it as “Paris mean time delayed by 9 minutes and 21 seconds” (5).
The 1884 conference selected a common prime meridian and a universal day, but it did not formally divide the world into the 24 time zones used today. That system became established gradually through national legislation and practical decisions. The present map of time zones is the result of more than a century of political change rather than a single international act of drawing lines around the world.
Paris Observatory
Royal Observatory, Greenwich
25 countries, 22 votes for Greenwich
France adopts the Greenwich-based standard
Why time zones do not follow meridians
Six places where the clock departs from simple geometry
Close to Greenwich in longitude, aligned with Central European Time.
One official time across a territory spanning about five geographical zones.
The widest global spread when overseas territories are included.
A half-hour offset used across the entire country.
One of the world’s few 45-minute offsets.
A line that bends around states and island groups.
If time zones were determined by geometry alone, the world could be divided into 24 approximately equal bands, each 15 degrees wide. The actual map is considerably more complicated. Boundaries follow states, administrative units, island groups and economic connections. In some cases, local clock time differs substantially from the solar time associated with a place’s longitude.
Spain is one of the best-known examples. Most of its mainland territory lies at longitudes close to those of the United Kingdom and Portugal, yet it uses Central European Time. Until 1940, the country followed Greenwich Mean Time. In an order dated 7 March 1940, Francisco Franco’s government instructed clocks to be moved forward by one hour so that Spanish time would run “in accordance with that of other European countries” (6).
The change is commonly associated with the Franco regime’s political alignment with Hitler’s Germany, although the order itself does not mention Germany and presents the measure as a temporary adjustment to other European countries. Spain did not return to its previous time zone after the Second World War. Official time consequently runs ahead of mean solar time, especially in the western parts of the country. This is often considered one factor behind Spain‘s comparatively late daily schedule for work, meals and sleep, although the country’s social rhythm cannot be explained by its time zone alone.
China follows a different approach. Its territory extends geographically across approximately five time zones, yet the entire country uses a single official time, UTC+8, known as Beijing Time. One zone simplifies state administration, national communications and transport. In the far west, however, the Sun rises and sets much later according to the official clock. In Xinjiang, an unofficial local time two hours behind Beijing Time is also used. A single administrative system therefore operates alongside local everyday practices.
Large countries may choose another solution. Russia uses 11 time zones, while the United States has several zones across its contiguous territory, Alaska, Hawaii and its island territories. Managing such countries depends on clearly stating local time, coordinating transport schedules, and using UTC in aviation, meteorology, science and information systems.
France is often identified as the country with the greatest number of time zones when its overseas territories are included. These territories lie across the Atlantic, Indian and Pacific oceans and extend through both the Western and Eastern hemispheres. Metropolitan France uses one zone, while each distant territory follows a local time appropriate to its location.
Time zones with offsets that are not whole hours add another layer to the map. India uses UTC+5:30, Nepal uses UTC+5:45, and several territories have 30-minute offsets. Because of these variations and the seasonal use of daylight saving time, more than 24 different local clock times may exist around the world at once. As of July 2026, 38 different local UTC offsets are in use (7).
The International Date Line also responds to political and economic needs. It follows the 180th meridian approximately, but deviates from it to avoid dividing certain countries and island groups between two calendar dates. At the same physical moment, two consecutive dates can therefore be recorded on opposite sides of the line.
What year is it now?
What Year Is It Around the World?
Select a country to compare the calendar systems used there and see values calculated for today.
The most common answer to the question “What year is it now?” is “2026” because the Gregorian calendar has become the principal international standard for civil use, trade, transport, scientific exchange and digital communication. The international standard ISO 8601 defines an unambiguous way to represent dates and times in the sequence year, month and day, for example 2026-07-24. The standard uses the Gregorian calendar and allows time to be written in UTC or with an offset from it (8).
This standardisation still leaves room for many calendar systems. Calendars connect astronomical cycles with religious beliefs, historical events and state traditions. Different systems may begin from another epoch, divide the months differently, and apply their own rule for the start of a new year.
At the time of writing, the Gregorian calendar year is 2026, while the Hebrew calendar remains in the year 5786. It began in the autumn of 2025 and will end at the next Rosh Hashanah in September 2026. The Hebrew calendar is lunisolar: its months follow lunar cycles, while the insertion of an additional month in certain years keeps religious festivals in their appropriate seasons.
In Islamic calendars, the year is already 1448 AH. The era begins with the migration of the Prophet Muhammad and his followers from Mecca to Medina in 622 CE. An Islamic year contains 12 lunar months and is approximately 10 or 11 days shorter than a solar year. Ramadan and the other months therefore move gradually through all seasons. The precise date may differ by one day between countries and religious communities because the beginning of a month is determined through different methods, including observation of the Moon, astronomical calculation and official declaration. Several calendar variants are used within the broader category of the Islamic calendar (9).
In Ethiopia, the year is 2018 for most of 2026, with 2019 beginning in September. The Ethiopian calendar has 13 months: twelve months of 30 days and a short thirteenth month of five or six days. Its difference from the Gregorian calendar arises from a different calculation and the calendar system’s own historical tradition.
Nepal officially uses the Bikram Sambat calendar, in which July 2026 falls in the year 2083. The Thai Buddhist calendar identifies the same Gregorian year as 2569. In India, the Gregorian calendar is widely used alongside the official national Saka calendar, whose year is 1948. The Bengali calendar, used in different forms in Bangladesh and parts of India, shows the year 1433.
Japan combines international year numbering with the traditional system of imperial eras. The Reiwa era began when Emperor Naruhito ascended the throne in 2019, which makes 2026 Reiwa 8. Under this system, the year is counted from the beginning of the current emperor’s reign rather than from an ancient religious or astronomical epoch.
In the traditional Chinese calendar, years form part of a 60-year cycle that combines ten Heavenly Stems and twelve Earthly Branches, the latter also associated with the twelve zodiac animals. The Year of the Fire Horse began on 17 February 2026. The same combination recurs once every 60 years (10). China uses the Gregorian calendar for civil and administrative purposes, while the traditional calendar continues to determine festivals, rituals and cultural practices.
Everyone lives within the same physical passage of time, while societies organise it through different historical systems. An international civil calendar, a national calendar and one or more religious calendars may operate simultaneously within the same country. The answer to “What year is it now?” therefore depends on both the place and the context in which the question is asked.
Gregorian
Hebrew
Islamic
Ethiopian
Bikram Sambat
Japan
Calendar years begin on different dates, so these values describe July 2026 and change according to each system’s own rules.
Time as a natural process and a social decision
The measurement of time begins with natural processes: the Earth’s rotation, its orbit around the Sun, the phases of the Moon and stable oscillations within atoms. Converting these processes into seconds, time zones, dates and years requires human choices.
Atomic clocks provide a common second, while states decide which time zone to use. Astronomical cycles determine the approximate lengths of the day, month and year, while religions and cultures choose the epoch from which years are counted and the rules used to reconcile solar and lunar cycles. The history of the Greenwich and Paris meridians shows how closely science can be connected with political influence, economic power and international negotiation.
The maps of time zones and calendar years allow us to examine this system geographically. They show the boundary between measurement and convention: nature provides the rhythms, while societies decide how to count them.
Nature and physics
Rotation, orbit, lunar phases and atomic oscillations provide the measurable rhythms.
Societies and states
Time zones, calendar eras and legal standards determine how those rhythms are counted.
Sources
- Bureau International des Poids et Mesures. The BIPM and the Metre Convention. Information about international metrology, the SI and the Metre Convention. https://www.bipm.org/en/
- Bureau International des Poids et Mesures. Time Metrology. Information about International Atomic Time (TAI), Coordinated Universal Time (UTC) and the relationship with the Earth’s rotation. https://www.bipm.org/en/time-metrology
- International Meridian Conference. Protocols of the Proceedings, Washington, 1884. Primary historical source containing the conference proceedings, resolutions and votes. https://www.gutenberg.org/files/17759/17759-h/17759-h.htm
- Royal Museums Greenwich. What is the Prime Meridian, and why is it in Greenwich? History of the Greenwich meridian and the role of maritime navigation in its selection. https://www.rmg.co.uk/stories/time/what-prime-meridian-why-it-greenwich
- Mautz, R. International Meridian Conference (1884). Historical account of the Paris and Greenwich meridians and the adoption of Greenwich time in France. https://www.thegreenwichmeridian.org/tgm/articles.php?article=10
- Government of Spain. Orden de 7 de marzo de 1940 sobre adelanto de la hora legal en sesenta minutos. Boletín Oficial del Estado, 8 March 1940. Cited in the historical documentation of legal time in Spain. https://www.boe.es/datos/pdfs/BOE//1940/068/A01675-01675.pdf
- Time and Date AS. How Many Time Zones Are There? Current overview of UTC offsets in use, including half-hour and 45-minute time zones. https://www.timeanddate.com/time/current-number-time-zones.html
- International Organization for Standardization. ISO 8601-1:2019: Date and time. International standard for representing dates and times using the Gregorian calendar. https://www.iso.org/standard/70907.html
- Unicode Consortium. Common Locale Data Repository: Calendar Systems. Technical documentation for internationally used calendar systems and their variants. https://www.unicode.org/cldr/charts/latest/summary/en.html
- Smithsonian Institution. 2026: Year of the Horse. Information about the beginning of the Chinese Year of the Fire Horse on 17 February 2026. https://www.si.edu/spotlight/lunar-year-horse