“525,600 minutes, how do you measure, measure a year? In daylights, in sunsets, in midnights, in cups of coffee…”

The title is a part of the lyrics to the song “Seasons of Love” in the musical Rent.? This document starts with a look back in history and provides a summary of how some of the World’s greatest civilizations measured a year and some of the various definitions of Year 1 (because there is no Year 0!). The problem is that the actual length of a day is 23 hours, 56 minutes, 4 seconds; a month is 29.53 days and a year 365.2422 days – making it difficult to devise an exact calendar that is easy to follow.

The Romans during the time of Julius Caesar formed the Julian Calendar and are credited for putting in place the foundations of the calendar the majority of the world use today.? Caesar commissioned astronomer Sosigenes to improve things – the result being that each month now had either 30 or 31 days except February, which contained 28 days and 29 in every fourth year.? However, under the Julian Calendar January wasn’t the first month of the year – instead it started in March and ended in February.

It wasn’t until 1582, however, that the calendar much of the world uses today was devised. It was called the Gregorian Calendar after Pope Gregory XIII who wanted to get the calendar back in sync with seasonal events like the spring equinox and winter solstice by removing some days and working out leap years more accurately.Although many of the southern European Catholic countries adopted the new system almost straight away, some Protestant countries resisted for many years. Germany didn’t change over until 1610 while the UK and the US held out until 1752. Greece and Islamist Turkey didn’t fall in line until the 1920s.

The Romans were not the first civilisation to measure time; the earliest calendars date back to the Bronze Age with civilisations in the near east region, such as the Babylonians and Persians, being among the first to record time by using natural cycles including days, lunar cycles (months), and solar cycles (years).

The Egyptians are generally credited as the first to make all their months an even 30 days – moving away from early attempts of trying to synchronise with lunar cycles and focusing instead on aligning with the solar year. They also introduced the concept of a leap year every four years.? The Aztecs developed a very similar calendar called Xiuhpōhualli (year (xihuitl) count (pōhualli)).

During the 17th century, the Jesuit missionaries tried to determine the epochal year of the Chinese calendar. In his Sinicae historiae decas prima (published in Munich in 1658), Both? Martino Martini (1614–1661) and later Philippe Couplet's 1686 Chronological table of Chinese monarchs (Tabula chronologica monarchiae sinicae) dated the Yellow Emperor's ascension at 2697 BCE (Before Common Era) and began the Chinese calendar with the reign of Fuxi. ? Publications began using the estimated birth date of the Yellow Emperor as the first year of the Han calendar in 1903, with newspapers and magazines proposing different dates which meant that? 2024 CE (Common Era) would have varied between 4396 and 4735, a fairly large variation (339 years or 7.4% of the middle of this range).? Taoists later adopted the Yellow Emperor Calendar and named it Tao Calendar.? On 2 January 1912, Sun Yat-sen changed it once more making 2024 CE equivalent to the year 4722.? The modern Chinese standard calendar uses the epoch of the Gregorian calendar, which is on 1 January of the year 1 CE.

The Ge'ez calendar is the official calendar of Ethiopia. It is used as both the civil calendar and an ecclesiastical calendar.? It is a solar calendar that has much in common with the Coptic calendar of the Coptic Orthodox Church of Alexandria and Coptic Catholic Church, but like the Julian calendar, it adds a leap day every four years without exception; the year on 11 or 12th of September in the Gregorian calendar (from 1900 to 2099). A gap of seven to eight years between the Ethiopian and Gregorian calendars results from an alternative calculation used to determine the date of the Annunciation.? The Ethiopian calendar has twelve 30-day months, all thirty days long, as well as a five- (or six-) day 13th month; all months begin on the same days as those of the Coptic calendar. ? A sixth day is added every four years, without exception, on 29 August of the Julian calendar, and not 29 February. Thus, the first day of the Ethiopian calendar year, for years between 1900 and 2099 (inclusive), is usually 11 September (Gregorian).

Like other lunisolar calendars, the Hebrew calendar consists of months of 29 or 30 days which begin and end at approximately the time of the new moon. As 12 such months comprise a total of just 354 days, an extra lunar month is added every 2 or 3 years so that the long-term average year length closely approximates the actual length of the solar year.? Originally, the beginning of each month was determined based on physical observation of a new moon, while the decision of whether to add the leap month was based on observation of natural agriculture-related events in ancient Israel.? Between the years 70 and 1178, these empirical criteria were gradually replaced with a set of mathematical rules. Month length now follows a fixed schedule which is adjusted based on the molad interval (a mathematical approximation of the mean time between new moons) and several other rules, while leap months are naow added in 7 out of every 19 years according to the Metonic cycle.? Nowadays, Hebrew years are generally counted according to the system of Anno Mundi "from the creation of the world", abbreviated AM. This system attempts to calculate the number of years since the creation of the world, according to the Genesis creation narrative and subsequent Biblical stories. The current Hebrew year, AM 5784, began after sunset on 2 October 2024.

The Solar Hijri calendar is just one of various Iranian calendars. It begins on the March equinox as determined by the astronomical calculation for the Iran Standard Time meridian (52.5°E, UTC+03:30) and has years of 365 or 366 days. It is the modern principal calendar in Iran and Afghanistan and is sometimes also called the Shamsi calendar and Khorshidi calendar.? The ancient Iranian Solar calendar is one of the oldest calendars in the world, as well as the most accurate solar calendar in use today. Since the calendar uses astronomical calculation for determining the vernal equinox, it has no intrinsic error and It is older than the Lunar Hijri calendar used by the majority of Muslims (known in the West as the Islamic calendar); though they both count from the Hijrah, the journey of the Islamic prophet Muhammad and his followers from Mecca to Medina in the year 622,? one uses solar years and the other lunar years.? The first six months have 31 days, the next five have 30 days, and the last month has 29 days in common years but 30 days in leap years.? The ancient Iranian New Year's Day, which is called Nowruz, always falls on the March equinox. While Nowruz is celebrated by communities in a wide range of countries from the Balkans to Mongolia, the Solar Hijri calendar itself remains only in official use in Iran.? As with the Solar Hijrah, the Lunar Hijrah also uses the same epoch (first year) corresponds to the Hijrah in 622, but as one is Solar and the other is a lunar calendar, the two calendars' year numbers do not coincide with each other and are slowly drifting apart, being about 43 years apart as of 2023.

The Juche calendar, named after the Juche ideology, is the system of year-numbering used in North Korea. It begins with the birth of Kim Il Sung, the founder of North Korea. His birth year, 1912 in the Gregorian calendar, is "Juche 1" in the Juche calendar. The calendar was adopted in 1997, three years after the death of Kim Il Sung. (Just as this article was published, the BBC announced that North Korea is abandoning the Juche calendar and has adopted the Gregorian calendar.)

Apart from the starting date, the Buddhist calendar is identical to the Western Gregorian calendar - you can calculate the Buddhist year in Thailand by simply adding 543 to the Gregorian year. For example, the Western year 2000 corresponds to the Thai Buddhist year 2543, and 2022 to the Thai Buddhist year 2565,? This is still very much in use and actually appeared as a visit date in our database for a participant in a trial being run at a very traditional Buddhist hospital that was using their own iPad (a risk to adopting a Bring Your Own Device (BYOD)!

The History of Coordinated Universal Time (UTC)

Establishment of Universal Time

In 1884, with many countries outside of Europe using their own calendars, 26 countries from around the world converged in Washington, DC, for the International Meridian Conference. The purpose of this meeting was to set a specific longitude coordinate on Earth as zero, thereby allowing people in different countries to follow a common system of coordinated time zones. This zero-degree coordinate was called the Prime Meridian, and it intersected with the Royal Observatory in Greenwich, England. This made the local time of that area, Greenwich Mean Time (GMT), the global standard. At this point, people kept time by directly observing astronomical features, hence the choice of the observatory. In this way, Universal Time (UT), based solely on the rotation of Earth, came into existence. ? The issue with this method for keeping time was that it was not extremely precise and could be difficult to reference for those who were farther from the Prime Meridian. This is mostly due to the fact that the time it takes the Earth to rotate on its axis actually changes instead of remaining constant. In 1955, however, Louis Essen invented the world’s first cesium atomic clock. This device keeps track of the vibratory changes in the energy state of cesium atoms when exposed to radio waves, recording the radio wave frequency that results in the most vibrating cesium atoms being used to define a one second period, formally becoming the SI Unit in 1967, defined as the frequency length of the radio wave (9,192,631,770 Hertz).

Creation of Coordinated Universal Time

The atomic clock was suitable for use anywhere and that it maintained a high level of accuracy.? Radio waves were used to broadcast time signals. In 1960, the Greenwich Observatory, the UK National Physical Library, and the US Naval Observatory synchronized their radio signals, creating Coordinated Universal Time. In 1961, the Bureau International de l’Heure (International Time Bureau) introduced Coordinated Universal Time across the globe on all continents apart from Antarctica

UTC underwent further adjustments to take both atomic references and the Earth’s rotation into account. Thus, from 1972 onwards, the International Earth Rotation and Reference Systems Service has added a leap second to UTC when changes in the Earth’s rotation cause UTC to fall greater than 0.9 seconds behind UT.

Nowadays almost all computers measure time in UTC, regardless of where in the world you are based; this would be challenging to use as a standalone reference point - for example if UTC was the standard displayed time and you took a flight from London to Singapore, the flight time is 13 hours (rounded to the nearest hour) so in UTC a flight commencing at 01:00 UTC would land in Singapore at 14:00 UTC, but this would be hard to comprehend as 14:00 UTC in London may be be night time, but daylight in Singapore and a knowledge as to what time breakfast is in UTC in Singapore would be totally different compared to Australia, USA, India etc.? Thus the computers also store the offset from 0:00 longitude and governments choose which timezone(s) their Country should align with as well as whether the country was observing daylight saving adjustments.? Daylight saving adjustments are also subject to be either added or dropped by governments and so it is essential to maintain subscriptions to databases that store up-to-date information.

The Medable platform is no different and the system clock is used to record timestamps of all measurements from simple diaries to integrated blood pressure monitors.? Whilst the data are stored as UTC, all modern programming languages have built-in functions that combine the UTC time with the stored offset to produce the local time where the measurement was performed.? The use of electrronic timestamps removes the big unknown that exists with paper-based systems, namely that this relies on the reliability (honesty) of the participant to record the actual time of completion; it also opens up the potential for analysis of the time taken to complete a diary or eCOA, something that could be used to monitor participant engagement over the duration of the study.

To answer the question posed by the title, I measure a year in the frequency of caesium atoms, but perhaps cups of coffee is more appealing!