Time is the progression of events through the past, present, and future. The study (or science) of time is known as chronology. The word chronology was first used in the 1590s and meant “the science of time”.[1] Chronology is a combination of “chronos” (time) and “logos” (study/science). There is however another study known as horology, which is also defined as the study or science of time. The word horology was first used in 1752 to mean “science of time”. Horology ultimately derives from a word meaning “instrument for telling the hour”.[2] Put simply, horology is the science of timekeeping, or “the science of telling time”.[3, p.17]

The main difference between the two is that chronology is typically concerned with determining the order in which past events occurred while horology is typically concerned with studying time for the purpose of creating time keeping devices, such as clocks or sundials. Both studies are important for understanding what time is and how it affects us.

Many languages across the world have a word for time. Here’s a list I made that includes the word for time in 36 different languages:

Arabic: زمن (zaman)
Bangla: সময় (Samaẏa)
Bosnian: Vrijeme
Bulgarian: Време (Vreme)
Chinese: 时间 (Shíjiān)
Croatian: Vrijeme
Czech: Čas
Danish: Tid
Dutch: Tijd
English: Time
Estonian: Aeg
Finnish: Aika

French: Temps
German: Zeit
Greek: χρόνος (cronos)
Hebrew: זְמַן
Hindi: समय (samay)
Hungarian: Idő
Irish: Im
Italian: Tempo
Indonesian: Waktu
Japanese: 時間
Latvian: Laiks
Lithuanian: Laikas

Maltese: Ħin
Polish: Czas
Portuguese: Tempo
Romanian: Timp
Russian: Время (Vremya)
Slovak: Čas
Slovenian: Čas
Spanish: Hora
Swahili: Wakati
Swedish: Tid
Turkish: Zaman
Ukranian: Час (Chas)

“Science is dependent on the accurate measurement of time.”
– Ken Mondschein, On Time[3, p.3]

Timekeeping and astronomy have not always been readily available to common people. It’s not peculiar to find in many eras of history that these disciplines were exercised only by limited groups of privileged individuals.[3, p.11]

The use of AM (ante meridiem) and PM (post meridiem) denotes before (AM) and after (PM) noon.

“Time was one of the great breakthrough ideas in the history of thought.”
– Felipe Fernández-Armesto (2019)[8, p.65]

Timekeeping is not dependent on clocks. We can use other things to use as a reference point, such as how long a candle takes to burn or how long it takes to say a prayer. What timekeeping is dependent on is movement. It requires the movement of one object in relation to another.

A solar year is about 365.24 days and it is synced with the seasons. A lunar month contains about 29.53 days. There’s no way to fit an equal amount of lunar months into a solar year. Twelve lunar months is shorter by about 11 days and 13 lunar months is longer by about 18 days. This would result in:

12lunar months:
1 year: -11 days
2: -22
3: -33
4: -44
5: -55
6: -66
7: -77
8: -88
9: -99
10: -110
11: -121
12: -132
13: -143
14: -154
15: -165
16: -176
17: -187
18: -198
19: -209
20: -220

13 lunar months:
1 year: +18 days
2: +36
3: +54
4: +72
5: +90
6: +108
7: +126
8: +144
9: +162
10: +180
11: +198
12: +216
13: +234
14: +252
15: +270
16: +288
17: +306
18: +324
19: +342
20: +360

Units of Time

The following units of time are defined according to the common usage today. Over time these words have had different quantifications and definitions.

A Second: is 1/60 of a minute.[5]

A Minute: is 1/60 of an hour. There are 60 seconds in a minute.[5]

An Hour: is 1/24 of a day. There are 60 minutes in an hour. There are 3,600 seconds in an hour.[5]

A Day: is based on the sun passing through the celestial meridian. This portion of time has been split into 24 parts which are called hours. There are 1,440 minutes in a day. There are 86,400 seconds in a day.[5]

The Babylonians, Chinese, Egyptians, and the Indus Valley civilizations all divided their days into 24 sections. Twelve sections for the night and twelve sections for the light. It’s currently unknown where this practice originated.[3, pp.9-10]

A day being split between light and dark can sometimes complicate how “a day” is perceived. The summer solstice is the longest day of the year while the winter solstice is the shortest. This is why the longest day in Paris can have more than 16 hours and 10 minutes of sunshine while the shortest day of the same year can have only 8 hours and 15 minutes.[3, p.20] The Spring and Fall equinoxes are the only two days in the year where the day and night are exactly equal.[3, p.203]

A Week: is seven days. It contains 168 hours. It contains 10,080 minutes. It contains 604,800 seconds.[5] The seven day week was first introduced in the 1st century CE and the days themselves were named after the 7 classical planets (the sun, the moon, Mercury, Venus, Mars, Jupiter, and Saturn).[3, p.24]

A Month: is 28-31 days.[5]

A Year: is 365.24 days.[5]

A Decade: is 10 years.[5]

A Century: is 100 years.[5]

A Millennium: is 1,000 years.[5]

A Mega-anuum: is 1,000,000 years.[5]

Types of Hours

Canonical Hours: The 8 times throughout the day when Christian monks were required to pray, namely Matins, Prime, Tierce, None, Sext, Vespers, Compline, and Laudes.[3, p.200-201]

European Hours: ???.[3, p.143]

French Hours: 24 hours that begin at midnight.[3, p.63]

Italian Hours: 24 hours that begin at sunset.[3, p.62]

Ottoman Hours: ???.[3, p.143]

Seasonal Hours: is another term for unequal hours.[3, p.207]

Unequal Hours: These are varying sections of the day split into 12 parts and the night split into 12 parts. These hours were common in Europe and China.[3, p.21] While fixed hours eventually became the most popular in our current day, unequal hours were still in use in throughout the 1800’s by a number of Mediterranean populations.[10, p.16]

Types of Days

“Again, the British, in common with the French, Germans, and the Americans, count a new day as beginning so soon as midnight of the previous one has struck. The modern astronomers in all countries take twelve o’clock noon (local time) as the starting point of the day.”
James Cecil Macdonald (1897)[7, p.79]

“The beginning of a new day to each of the Jews, Austrians, and Chinese is sunset; and sunrise among the modern Greeks and the Persians.”
James Cecil Macdonald (1897)[7, p.80]

Bickerman reported that the day began at sunrise for the Babylonians, Egyptians, Greeks, and Romans.[10, p.13]

Conjunction Days[9, p.ix]

Epagomenal Days[10, p.48]

Fast Days[9, p.viii]

Halcyon Days: “…the seven days of both sides of the shortest day.”[7, p.80]

Holidays[9, p.viii]

Mean Solar Day: 24 hours.[3, p.16]

Personal Days[9, p.viii]

Solar Day: One revolution of the earth on its axis.[10, p.9]

Sidereal Day: 23 hours, 56 minutes, and 4 seconds. It is determined by the stars returning to the same spot in the sky.[3, p.16]

Types of Weeks

Weeks can be composed of different amounts of time. Typically they are groupings of days. Some weeks have 4 days while others have 5 days. Additionally, 6-day, 7-day, 8-day, and 10-day weeks all exist too.[9, p.5]

Astrological Week[10, p.61]

Astronomical Week[10, p.61]

Jewish Week[10, p.61]

Market Week: 8 days. 7 working days and 1 market day.[10, pp.58-59]

Planetary Week[10, p.61]

Types of Months

Embolismic Months[10, p.29]

Full Month: 30 days.[6, p.29]

Hollow Month: 29 days.[6, p.29]

Lunar Month: 29.53059 days.[6, p.12]

Sidereal Month: 27.32 days. It is determined by the moon returning to the same spot against the stars.[3, p.207]

Synodic Month: 29.53 days. It is determined by the moon completing one cycle of its phases.[3, p.22]

Zodiacal Month:[6, p.12]

Types of Years

“Even in our own country, there are several sorts of years – the civil, fiscal, leap, and common years.”
James Cecil Macdonald (1897)[7, p.79]

Achaean Year[10, p.76]

Administrative Year[6, p.88]

Agricultural Year[10, p.22]

Agrarian Year[10, p.44]

Alexandrian Year[10, p.48]

Archon Year[10, p.87]

Civil Year[10, p.63]

Consular Year[10, p.72]

Ecclesiastical Year[10, p.63]

Egyptian Year[10, p.40]

Embolismic Year[9, p.114]

Eponymous Years[10, p.67]

Farmer’s Year[10, p.52]

Financial Year[10, p.58]

Fiscal Year[10, p.63]

Gravid Year[9, p.114]

Julian Year[10, pp.47, 63]

Leap Year[9, p.114]

Lunar Year[6, p.12]

Lunisolar Year[10, p.22]

Macedonian Year[10, p.76]

Mariner’s Year[10, p.52]

Mobile Year[10, p.81]

Natural Year[10, pp.49, 52, 63]

Negative Years: These are years that count backwards from the beginning of an era. An example of this can be seen in BC dates, where they are reckoned backwards from the supposed year of Christ’s birth.[9, p.15]

Olympic Year[10, p.87]

Regnal Year[10, p.66]

Roman Years: Years counted from the founding of Rome (AUC, Ab Urbe Condita).[9, p.81]

Romulean Year[10, p.45]

Royal Year[10, p.65]

Sabbatical Years[9, p.115]

School Year[10, p.63]

Seasonal Year: See Solar Year.[6, p.12]

Sidereal Year: is determined by the sun returning to the same spot against the stars.[3, p.207] It contains 365.2564 mean solar days.[6, p.12]

Solar Year: 365.24 days. It’s the time it takes for the sun to return to the same tropic in the sky.[3, p.207] More specifically, 365.24219 mean solar days.[6, pp.8, 12] Bickerman defined the solar year as “365 days, 5 hours, 48 minutes, and almost 46 seconds”.[10, p.10]

Soldier’s Year[10, p.52]

Tropical Year: See Solar Year.[3, p.21], [6, p.12] One revolution of the earth around the sun.[10, p.9-10]

Zodiacal Year[10, p.57]

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[1] – https://www.etymonline.com/word/chronology. Accessed 21 Oct. 2020.

[2] – https://www.etymonline.com/word/horology. Accessed 21 Oct. 2020.

[3] – Mondschein, Ken, and Neal Stephenson. On Time: a History of Western Timekeeping. Johns Hopkins University Press, 2020. Accessed Jan. 2021.

[4] – Robert Hannah. “Time in Antiquity” (2008). https://www.google.com/books/edition/Time_in_Antiquity/rtN_AgAAQBAJ?hl=en&gbpv=0. Accessed 19 Dec. 2020.

[5] – https://www.exactlywhatistime.com/measurement-of-time/units-of-measurement/. Accessed 5 Jan. 2021.

[6] – Hannah, Robert. Greek and Roman Calendars: Constructions of Time in the Classical World. Illustrated, Bloomsbury Publishing Plc, 2005. Accessed Jan. 2021.

[7] – James Cecil Macdonald. “Chronologies and Calendars” (London, 1897). Accessed Jan. 2021.

[8] – Felipe Fernández-Armesto. “Out of Our Minds: What We Think and How We Came to Think It” (2019). Accessed Jan. 2021.

[9] – Edward M. Reingold & Nachum Dershowitz. “Calendrical Calculations: The Ultimate Edition” (Cambridge, 2018). Accessed 27 Jan. 2021.

[10] – E. J. Bickerman. “Chronology of the Ancient World” (1968). Accessed 30 Jan. 2021.

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