#water clock

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

This clepsydra is the oldest water clock of which there is physical evidence dates to ca. 1391-1353 BC, during the reign of Amenhotep III where it was used in the Temple of Amen-Re at Karnak. It was specifically designed to be independent from weather conditions that might limit the visibility of the sun or the stars, a necessary precondition for other methods.

The uppermost row shows decans and anthropomorphic representations of stars and planets depicted in barques. Below, in the middle row, are the more prominent constellations of the northern sky and deities on both sides.

The bottom row has six frames, each displaying the king, flanked by two of the twelve gods of the months. The outflow aperture is located between two of the frames.

The outside surface of this clepsydra, or water clock, is decorated with figures and text that show symbols of certain planets and constellations and give a list of the protective spirits for each of the ten days of the ancient Egyptian week.

The middle register, or section, is occupied by the circumpolar stars under the aspects of various gods and animals.