Timekeeping
Timekeeping goes far back in human history, with the movements of the celestial bodies across the sky as well as the movements of the moon and constellations through the year. With the rise of cities and more regulated society began to have observances that had to be kept at particular times through the day.
By Gaffney, V et al 2013 Time and a Place: A luni-solar 'time-reckoner' from 8th millennium BC Scotland, Internet Archaeology 34. https://doi.org/10.11141/ia.34.1 - https://intarch.ac.uk/journal/issue34/1/images/figure10.html, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=125576972
The first timekeeping devices were monumental works that could be used as astronomical observatories, marking equinoxes and solstices. Because of a lack of writing from this era of human history, it's difficult to know what the observations were and how they used the megalithic monuments left behind. The oldest known lunisolar calendar is Warren Field in Aberdeenshire, Scotland, which has topographic points that line up with the winter solstice and 'thus providing an annual astronomical correction concerning the passage of time as indicated by the Moon, the asynchronous solar year, and the associated seasons'. It dates to about 8,000 BCE. Among the Mesoamericans, they used a base-20 numerical system, which continued through to how they kept track of the days of the year, with multiple interlinked cycles based on the 20 day cycles to give them a Calendar Round when dates will repeat after 18,980 days, or approximately 52 solar years, or a lifetime. The Australian Aboriginal peoples had multiple calendars and passed them down orally, with some groups, especially those in the north, counting six seasons rather than the European four, with the rising of certain constellations marking the beginning of the season. There are some stone formations that seem to have pointed to or confirmed the solstices or equinoxes, but how old those formations are is uncertain.
By Rudolphous - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=63412618
The first measuring devices that measured the position of the sun throughout the day were shadow clocks, which are made from a flat surface and an object to create a shadow known as a gnomon with the oldest known sundial being from about 1200 BCE and was found in the Valley of the Kings in Egypt. The flat surface is then divided into usually 12 sections as many civilizations around the Mediterranean used a 24 hour day with 12 hours in the day and the night. The Greeks used sundials that used the origins of trigonometry to create sundials that were specific to various latitudes. The Romans 'inherited' the Greek sundial when they looted one from Catania in Sicily. Titus Maccius Plautus, a Roman playwright who lived around 254-184 BCE, complained about the dominion of timekeeping when he wrote: 'The gods confound the man who first found out How to distinguish hours! Confound him too, Who in this place set up a sundial, To cut and hack my days so wretchedly Into small portions—When I was a boy, My belly was my sun-dial: one more sure, Truer, and more exact than any of them. This dial told me when 'twas proper time To go to dinner, when I had aught to eat— But now-a-days, why, even when I have, I can't fall to, unless the sun gives leave. The town's so full of these confounded dials, The greatest part of its inhabitants Shrunk up with hunger, creep along the streets.'
By Amitchell125 - Own work, based on Meridian on celestial sphere.png, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=105539264
Time at night was a bit more complicated. The Egyptians used a method that involved a north-south alignment of two plumb-lines called merkhet, lining them to Polaris and then observing when various stars cross that meridian, a technique that had been used since at least 600 BCE. This required detailed knowledge of the night sky through the year.
By Daderot - Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=41345142
Going back to at least 1500 BCE, water clocks, or clepsydra, that allow water to escape at a constant speed to determine times between hours have been used in Egypt, with Amenemhet being credited as the inventor with the oldest known water clock being found in the tomb of Amenhotep III, the pharaoh of Egypt from about 1417-1379 BCE. There are written descriptions of water clocks in Mesopotamia, but none have been found yet. It's likely that the water clock traveled through Mesopotamia to China during the Shang dynasty, which lasted from about 1600-1046 BCE. In China, the water clock was developed in different directions, including overflowing water clocks and developed water-driven astronomical clocks by 721 CE. Plato, Greek philosopher who lived from about 428-348 BCE, is reported to have invented an alarm clock that dropped lead balls dropping into a copper platter to wake his students.
