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As my kids are counting down to Christmas, I came to wonder how did people measure time through history. More precisely I wonder about unit systems for precision time keeping of years past gone.

I am wondering this, because the other two most prominent units (length and mass), have had many systems of units, which still echo from the past (some louder some less so). So even though I know of fathoms and leagues or slugs and stones, I don't ever remember encountering any other unit system other than that of second, hour, day, month, year.

I've checked Wikipedia at History of timekeeping devices, but only devices are mentioned (see hourglasses, burning incenses etc). However, nothing I could find about the actual names of units.

Has anyone else found the names of the actual units?

UPDATE: Thanks everybody for their responses. All of the answers so far for me had merit, even though on hindsight the question was not strictly engineering - it is more on measuring, which I perceive as a vital part of engineering. I've got to admit that the response is even better that I had hoped. I learned a lot of new things. Hopefully, there will be in time even more informational answers.

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    $\begingroup$ Fortnight perhaps? $\endgroup$ – Eric S Dec 21 '20 at 20:21
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    $\begingroup$ Engineering pervades everything, and an understanding of applicable units seems to me to be entirely fair. I remember interminable train journeys during my student days, counting the rail lengths and suddenly realising that they were fractional furlongs... rule of thumb: if it huts when dropped on your foot it's engineering :-) $\endgroup$ – Mark Morgan Lloyd Dec 21 '20 at 20:58
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    $\begingroup$ Engineering pervades everything - Actually, everything can go on the Mathematics site: Obligatory XKCD $\endgroup$ – manassehkatz-Moving 2 Codidact Dec 22 '20 at 3:34
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    $\begingroup$ @EricS: fornight is still used in some parts of the world. That might also be a generational thing in those places. $\endgroup$ – Fred Dec 22 '20 at 4:38
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    $\begingroup$ Re: fortnight. There is no other good word for a two-week period. Bi-weekly is ambiguous, it can either mean semi-weekly (twice a week) or fortnightly. $\endgroup$ – Flydog57 Dec 22 '20 at 5:04
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For most of China's history, a system of decimal time was used along side duodecimal time.

As part of the Metric System, the French tried to introduce decimal time, where 12 duodecimal hours would be replaced by 10 decimal hours.

In 1998, the Swiss watch company Swatch introduced a system of decimal time called Internet Time, where 1 day is divided into 1000 decimal minutes called beats.

KerMetric time divides 24 hours into 100 Kermits.

During the Medieval period a moment was a unit of time where 40 moments equaled one solar hour.

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  • $\begingroup$ Let's go back to moments! $\endgroup$ – Randy L Dec 22 '20 at 15:22
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    $\begingroup$ @RandyL: It makes the phrase "I'll be with you in a moment" more definitive. ;-) $\endgroup$ – Fred Dec 22 '20 at 15:36
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In European culture, hours have been used as the basic time interval since time immemorial. You will find a substantial amount of useful information on the relevant Wikipedia page.

However, until the universal adoption of mechanical timekeeping, hours were "unequal", defined as 1/12th part of the day or night with the length varying throughout the year.

Which gives me a good excuse to wish everybody a Happy Midwinter Solstice, since we are now at the point where the day (hence daylight unequal hours) is at its shortest, and the night (hence night-time unequal hours) is at its longest.

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  • $\begingroup$ Happy Midwinter Solstice to you too. $\endgroup$ – NMech Dec 21 '20 at 20:35
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    $\begingroup$ It's the summer soltice, I'll have you know. ;) $\endgroup$ – Joel Dec 22 '20 at 2:12
  • $\begingroup$ I'd really like to see a source for people dividing the day into hours of different length depending on the year. It would be completely impractical, because you would have to redefine every sundial and hourglass. (A sundial being as simple as the shadow a tree casts) $\endgroup$ – pipe Dec 22 '20 at 4:58
  • $\begingroup$ Whoever says to me in the future that engineers are not very sociable or that they dont have a sense of humor, one thing I'll definetely tell them is about my expeerience in this question. $\endgroup$ – NMech Dec 22 '20 at 5:03
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    $\begingroup$ @NMech I speculate that since trivial observation revealed that there were approximately twelve lunar months in the year (although in this era of excessive illumination such things continue to surprise some), it was considered appropriate to use the same number to divide up days and nights... rounded to the nearest integer which coincidentally was delightfully convenient to factorise into work/watch periods. Again by analogy: number of days in the year vs degrees in the circle. $\endgroup$ – Mark Morgan Lloyd Dec 22 '20 at 17:19
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Judaism has a long history of tracking both days and times. Most of this is centered around Jewish holidays, particularly the need for Passover to take place in the spring.

The basic date measurements are the day, lunar month (basically alternates between 29 and 30 days) and the year. The year is measured as a combination lunar/solar year, approximately 354 days in a regular (12 months) year and 383 days in a leap (13 months) year. Originally the months were set by witnesses of the new moon (the first sighting of the moon in the monthly cycle) and leap year determination was made based on a number of factors. Eventually a set cycle for the days of each month (most months always the same, Cheshvan and Kislev varying) and leap years (3rd, 6th, 8th, 11th, 14th, 17th and 19th years of 19 year cycle) was set. This was finalized sometime between ~ 850 and 1,700 years ago. See the fixing of the Hebrew calendar for more details.

Times are measured in two ways:

Seasonal hours (as mentioned in other answers) = 1/12th of the daytime or nighttime. These are used for determining times for prayers and other observances on a given day or night. For most calculations, a full hour or a large fraction thereof (e.g., Plag Hamincha = 1-1/4 seasonal hours before sunset) is used - precision to exact minutes and seconds is only practical today with modern clocks.

Absolute hours = 1/24th of a solar day. But in addition to hours, the calculations for the months (see above) actually goes down to Chalakim. There are 1,080 Chalakim per hour, or 3-1/3 seconds per Chelek. The key is that by measuring at the Chelek level, specifically 29 days 12 hours and 793 Chalakim per lunar month, the total Jewish calendar for 19 years works out to 365.2468222 days per solar years, incredibly close to the modern calculated value of approximately 365.2422 days - see Tropical Year for more details.

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  • $\begingroup$ After following the Chalakim link you had, I found out that "The helek derives from a small Babylonian time period called a she, meaning '"barleycorn", itself equal to 1/72 of a Babylonian time degree (1° of celestial rotation)" $\endgroup$ – NMech Dec 21 '20 at 20:30
  • $\begingroup$ Is the Judaic timekeeping still used actively? I mean not for religious purposes, but within a household for everyday activities, or in everyday phrases? $\endgroup$ – NMech Dec 21 '20 at 20:37
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    $\begingroup$ AFAIK, times pretty much just religious observances, though that includes prayer time every day. See myzmanim.com for calculation of these times into secular time for any place in the world. Calendar is used more broadly, particularly for ceremonial purposes even when not strictly for religious observance. For example Israeli independence day is the 5th of the month of Iyyar - I don't know what it is on the secular calendar. $\endgroup$ – manassehkatz-Moving 2 Codidact Dec 21 '20 at 20:49
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    $\begingroup$ Babylonian connections make sense. As I understand it, the Hebrew month names in common use are Babylonian in origin $\endgroup$ – manassehkatz-Moving 2 Codidact Dec 21 '20 at 20:50
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A non forgotten alternate variety of time is Unix Time, https://en.m.wikipedia.org/wiki/Unix_time which ignores leap seconds, and as such is slowly drifting away from UTC

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Depends on the culture and civilzation.

The romans had their civil day which had numerous subdivisions. See the wikipedia article below.

https://en.wikipedia.org/wiki/Roman_timekeeping#Civil_day

Monasteries had their own "canonical hours"

https://en.wikipedia.org/wiki/Canonical_hours

I'd imagine most people would just look at the sky to know what time it is. You can get pretty good at this. For some reason, I recall my scout master saying that you can know what time it is to within 15 minutes.

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  • $\begingroup$ Nice gum facts about siesta and noon in from the Roman link. $\endgroup$ – NMech Dec 22 '20 at 5:11
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History of Calendars has a lot about the longer units.

Probably the most extreme are the Mesoamerican people, such as the Mayans and Aztecs. The Mayans and Aztecs had two cycles, one being 260 days and the other being 365 (or 360?) days. That gives larger cycles of about 52 years. Then they used multiples of that to record even longer times. And they used a modified base 20 to record a lot of it. There's a lot of math involved.

Another interesting one is that even though the Romans used recognizable days, months, and years--they claimed that their original calendar had 10 months with 30-31 days each. I'm not a scholar of this, but people seem to think that they either had a long period of winter that wasn't considered to be part of any month, added in enough random days to keep the calendar lined up, or had a calendar that drifted so winter wouldn't always be in the same month. This is supposedly why the ninth, tenth, eleventh, and twelfth months are named seven (September), eight (October), nine (November), and ten (December).

Tangentially, on digital microwaves you can often enter up to 99 seconds without using minutes. One of my very engineering-minded friends found a lot of satisfaction in this. This will probably provide a lot of confusion for future historians.

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In ancient India, multiple hindu texts have measured time (kāla, which is eternal) ranging from microseconds to trillions of years. Some of these texts date back as far as 2nd millennium BCE. For example, Rig Veda - oldest known Vedic Sanskrit text - gives base / smallest unit of measurement as Paramāṇu (परमाणु) which is ≈ 25 µs. Longer measurement of time is based on lunar, solar, tropical and cosmic events - measuring in multiples of hours, days and years.

The Hindu calendar has been in use in the Indian subcontinent since the Vedic time, which is a lunisolar calendar. Unlike the Gregorian calendar which adds an extra day - it inserts an extra full month by complex rules, once every 32–33 months, to ensure that the festivals and crop-related rituals fall in the appropriate season.

On cosmic metrics, hindu mythologies suggests the time repeats in cycles of four yugas (चतुर युग - longest measurement of time) - namely Satya, Treta, Dvapara, and Kali⁠ - where eternal time repeats general events (symbolizing stages in rise and falls of humans). We are currently in the Kali yuga, last in the cycle.

Also, interestingly, there is also a concept of time dilation in the mythology (with no scientific explanation) - wherein different entities experience different elapsed time. There is also a suggestion that our forefathers experienced time slower than what we do.

Most of these ways to measure time is rarely used in modern India - their use is limited only to religious rituals.

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  • $\begingroup$ Thanks for this insight. $\endgroup$ – NMech Dec 23 '20 at 9:37
  • $\begingroup$ this was a very interesting chart $\endgroup$ – NMech Dec 23 '20 at 17:12

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