Was the "day" the first unit of time measurement?

Looking at our current system of time measurement from years down to seconds was the “day” base unit the unit that all other measurements were multiplyed or divided by?

Off of that did they figure “well, it seems like after so many days we go through a cycle of seasons. Lets count how many days it takes. Oh! It’s 365.”
Or was it later with astrology they figured “well, it seems like after so many days we make a circle around the sun. Let’s count how many. Oh! It’s 365.”

And how did they go from that to breaking it down into 12 months and seven day weeks?

How about the opposite direction? Why break a day down into 24 segments? And from there into 60 minutes of 60 seconds?

And if they knew a day had 24 hours why build a clock with only 12 hours??

If you can get your hands on an old Isaac Asimov book with a title something like The Clock We Live On (which was out of print last time I checked) you’ll find his version of how all this stuff came into being. It’s a fascinating read.

It wasn’t always that way. October was the eighth month at one time, for example. (“Oct”)

To be legible at a distance. They DO make 24 hour clocks, but the numbers are kinda small, and the divisions that seperate them kinda small. Google (images) “24 hour clock”.

Speculation: It seems natural to divide the day up into halves (day and night, dawn/sunset, as well as mid-day and mid-night). Mid-day and mid-night are roughly 12 hours apart, depending on your latitude. Eventually, names were given to the different parts of the day. “Meet me at Matins behind the pub.”

After a while, someone decided to come up with a measurement of how long the sun moved across a given arc of the sky (“x” number of degrees), and called it an hour, or sumthin. I forget all the reasons why more and more precise time measurement was needed. (One was ship navigation, when they need to take sun sightings preicisely at noon to figure out longitude, for example.)

Watch makers make round clocks (the gears that make the hands move are round, and produce a circular motion when you attach a pointer to them.). It was easy to divide that clock into 60 segments. (360 degrees in a full circle, 360 is nicely divided by 60. Figure out your circumference, divide that number by 60, and you know how far around that arc each minute mark is placed.)

Note that time has also been measured by candles that burn at steady rates, gravity driven clocks (like hour glasses) that use sand or water.

The ancient Romans defined an hour as 1/12 the time from sunrise to sunset, or sunset to sunrise. So in the summer, hours were longer during the day, and in the winter, they were longer at night.

Right. Originally there were 12 hours of day and 12 hours of night. And with sundials as the default timekeeper, those hours are going to vary in length.

So you have a day and a night. You want to divide the day up. You divide it into halves and you’ve got dawn, noon, dusk, and midnight. You divide the time between dawn and noon in half and so forth, and you’ve got dawn, mid-morning, noon, midafternoon, dusk, midevening, midnight, middawn, and dawn again.

You could keep dividing by halves, and then we’d have either 8 or 16 hours per day and night, except in ancient times people liked counting by dozens, so they divided up the day by dozens and the night by dozens. That’s just dividing the day into 4 parts and dividing each quarter into three parts.

Minutes and seconds followed after that, but 60=12*5. Convenient in a lot of ways, remembering that this was established before our current mania for decimalization, in fact, before the introduction of decimal numbering.

And people didn’t know that the earth traveled around the sun. A year measured the time between solar marks…soltices and equinoxes. Early calendars didn’t match months and days and years very precisely. And of course, months derive from the length of time it takes for the moon to cycle from full to new back to full again.

Weeks are totally arbitrary, although they are about 1/4 of a month.

Other months around October have the same feature. “Sept” is a prefix for “seven” (Latin septem, “seventh”). Then there’s an “Oct”, for eight, a “Nov” for nine, and a “Dec” for ten, all alterations of the Latin roots.

All this numbering of months was based on March being the first month of the year. January became first later in Rome’s history.

And of course “August” and “July” used to be named Sextilis and Quintilis until a certain two egomaniacs got them renamed after themselves.

Augustus Gloop and Julio Iglesias?

I thought the mania for divsiblity by 60 came from Babylonian math. But I could (ha) be wrong.

Out of print, perhaps, but used copies are available at amazon:


I’d order one right now, but am in the midst of replacing lost credit cards.

Thanks for the tip, Zeldar.

And the title you offered is spot on.

We don’t actually know which was “the first” unit of time measurement considered standard by any human society. The only definite evidence on early time units comes from textual records,* none of which AFAIK pre-date the existence of multiple standard time units. In other words, the earliest texts that attest to the concept of “day” also attest to similar concepts like “month” and “year”.

Time-periods attested in early texts include not only the “day” (less ambiguously, “day-and-night”, usually extending from sunrise to sunrise or sunset to sunset), but also:

  • “daytime” (sunrise to sunset),
  • “nighttime” (vice versa),
  • “month” (usually new moon to new moon or full moon to full moon), and
  • “year” (sometimes measured by events like solstices and equinoxes, as Lemur notes, and sometimes measured by the sun’s position with respect to a particular star), and
  • “season” (consisting of two to four months depending on the local climate).

Other early units that are probably (but I’m guessing here) later than the basic day/month/year concepts are the seven-day week, the “decad” or ten-day week, and the “watch” or one-third of daytime or nighttime. Possibly later than these are the Mesopotamian “beru” or “double-hour”, one-twelfth of a day-and-night, and “USH”, one-thirtieth of a “beru”. (Note that the “beru” was not usually a variable amount like the “seasonal hours” of classical and medieval timekeeping mentioned by Chronos, but rather a fixed-length time unit.)

Hours, minutes and seconds are modified versions of these time units in other ancient Near Eastern cultures. The general “sixtyness” of their subdivisions is due to the base-60 structure of the Mesopotamian number system, as MonkeyMensch noted.

Other types of time-designations were identified too, such as “morning”, “evening”, “twilight”, “winter”, etc. But I’m not aware of their being used as standard abstract time-units that could be used to measure other units. You would never speak of a “day-and-night” as being equal to “four mornings”, for example, in the way that you could speak of it as equal to twelve “beru” or twenty-four hours.

  • Yes, there are some prehistoric artifacts like the Ishango bone that may represent some kind of calendar system, but such interpretations aren’t conclusive.

Which correspond to the phases of the moon, and which are not arbitrary. It would be quite normal for people to notice when the moon looked like a full disk, and a half disk, and no disk, with the time interval being about 1 week between those phases.

I think the OP needs to specify which culture is being asked about. Some cultures had lunar based calendars and some had solar based calendars, and some had a combination of the two. It was the Egyptians from whom we get our 24 hour day (or 12 hour half-days), but from the Romans whom we get our yearly calendar of months, which, btw, was originally a lunar calendar, not a solar calendar (and they probably got theirs form the Greeks who got theirs from…). We really don’t know where the fixation with “12” came from, although it could be a counting method that used the number of phalanges on the fingers (not counting the thumb) or it could be from noticing (roughly) 12 full lunar cycles in a solar year. Or maybe it was something else altogether.

Which are actually two slightly different units. The former is called the tropical year, while the latter is the sidereal year, and they differ by about 1 part in 30,000. So over timescales of thousands of years, the two systems will fall out of synch with each other (this effect is called precession of the equinox). I’ve seen speculation that this was one contributor to the decline of ancient Egyptian civilizations: They kept track of the seasons via the Sun’s position relative to Sirius, or the sidereal year, but weather patterns, and the proper times to plant and harvest, correspond to the tropical year. So eventually, they ceased to be able to predict the flooding of the Nile (the most significant annual event in Egypt, and crucial for their agriculture) accurately.

There’s also yet another year, the time from perihelion to perihelion, but I can’t remember what that one is called, and it wouldn’t have been known to the ancients (or, indeed, to anyone before Kepler).