The ancient Egyptians were one of the first cultures to widely divide days into generally agreed-upon equal parts, using early timekeeping devices such as sundials, shadow clocks, and merkhets (plumb-lines used by early astronomers). [1] [2] Obelisks were also used by reading the shadow that they make[ citation needed ]. The clock was split into daytime and nighttime, and then into smaller hours.
Despite Herodotus's attribution of the invention of the sundial to the Babylonians in 430 BCE, the earliest known sundials were simple gnomons of Egyptian origin invented around 3500 BCE [ citation needed ]. More complex devices were developed over time, the earliest surviving one is a limestone sundial that dates back to 1500 BCE, discovered in the Valley of the Kings in 2013. [3] It was found in a housing area of construction workers and its division of daytime into 12 parts was possibly used to measure work hours. [3]
Shadow clocks were modified sundials that allowed for greater precision in determining the time of day, and were first used around 1500 BCE. [1] Their major innovation was a modified, more precise gnomon that allowed for the division of night time into 50 parts, with an additional two "twilight hours" in the morning and evening. The shadow clock gnomon was made up of a long stem divided into six parts, as well as an elevated crossbar that cast a shadow over the marks. This early clock was positioned eastward in the morning, while at noon it was rotated to face west to measure shadows cast by the setting sun. [1] The concept of measured shadows were adapted into larger, more public designs in the form of obelisks. Markers around the obelisk would indicate units of time, including morning and afternoon as well as the summer and winter solstices for ceremonial purposes. [1]
Using plumb-lines called merkhets , the Egyptians could calculate time at night, provided the stars were visible. [1] [2] Used since at least 600 BCE, two of these instruments were aligned with Polaris, the North pole star, creating a north–south meridian. [1] [2] By observing certain stars as they crossed the line created with the merkhets, they could accurately gauge time. [1] [2]
An hour is a unit of time historically reckoned as 1⁄24 of a day and defined contemporarily as exactly 3,600 seconds (SI). There are 60 minutes in an hour, and 24 hours in a day.
A sundial is a horological device that tells the time of day when direct sunlight shines by the apparent position of the Sun in the sky. In the narrowest sense of the word, it consists of a flat plate and a gnomon, which casts a shadow onto the dial. As the Sun appears to move through the sky, the shadow aligns with different hour-lines, which are marked on the dial to indicate the time of day. The style is the time-telling edge of the gnomon, though a single point or nodus may be used. The gnomon casts a broad shadow; the shadow of the style shows the time. The gnomon may be a rod, wire, or elaborately decorated metal casting. The style must be parallel to the axis of the Earth's rotation for the sundial to be accurate throughout the year. The style's angle from horizontal is equal to the sundial's geographical latitude.
Solar time is a calculation of the passage of time based on the position of the Sun in the sky. The fundamental unit of solar time is the day, based on the synodic rotation period. Traditionally, there are three types of time reckoning based on astronomical observations: apparent solar time and mean solar time, and sidereal time, which is based on the apparent motions of stars other than the Sun.
A water clock or clepsydra is a timepiece by which time is measured by the regulated flow of liquid into or out from a vessel, and where the amount of liquid can then be measured.
The Jantar Mantar is a collection of 19 astronomical instruments built by the Rajput king Sawai Jai Singh, the founder of Jaipur, Rajasthan. The monument was completed in 1734. It features the world's largest stone sundial, and is a UNESCO World Heritage Site. It is near City Palace and Hawa Mahal. The instruments allow the observation of astronomical positions with the naked eye. The observatory is an example of the Ptolemaic positional astronomy which was shared by many civilizations.
A quadrant is an instrument used to measure angles up to 90°. Different versions of this instrument could be used to calculate various readings, such as longitude, latitude, and time of day. Its earliest recorded usage was in ancient India in Rigvedic times by Rishi Atri to observe a solar eclipse. It was then proposed by Ptolemy as a better kind of astrolabe. Several different variations of the instrument were later produced by medieval Muslim astronomers. Mural quadrants were important astronomical instruments in 18th-century European observatories, establishing a use for positional astronomy.
The Solarium Augusti or Horologium Augusti was a monument in the Campus Martius of ancient Rome constructed in 10 BCE under the Roman emperor Augustus. It included an Egyptian obelisk that had first been erected under the pharaoh Psamtik II used in some fashion as a gnomon. Once believed to have been a massive sundial, it is now more commonly understood to have been used with a meridian line used to track the solar year. It served as a monument of Augustus having brought Egypt under Roman rule and was also connected with the Altar of Augustan Peace commemorating the Pax Romana established by his ending the numerous civil wars that ended the Roman Republic. The Solarium was destroyed at some point during the Middle Ages. Its recovered obelisk is now known as the Obelisk of Montecitorio.
The Obelisk of Montecitorio, also known as Solare, is an ancient Egyptian, red granite obelisk of Psamtik II from Heliopolis. Brought to Rome with the Flaminio Obelisk in 10 BC by the Roman Emperor Augustus to be used as the gnomon of the Solarium Augusti, it is now in the Piazza Montecitorio. It is 21.79 metres (71 ft) high, and 33.97 metres (111 ft) including the base and the globe.
The history of timekeeping devices dates back to when ancient civilizations first observed astronomical bodies as they moved across the sky. Devices and methods for keeping time have gradually improved through a series of new inventions, starting with measuring time by continuous processes, such as the flow of liquid in water clocks, to mechanical clocks, and eventually repetitive, oscillatory processes, such as the swing of pendulums. Oscillating timekeepers are used in modern timepieces.
The merkhet or merjet was an ancient surveying and timekeeping instrument. It involved the use of a bar with a plumb line, attached to a wooden handle. It was used to track the alignment of certain stars called decans or "baktiu" in the Ancient Egyptian. When visible, the stars could be used to measure the time at night. There were 10 stars for the 10 hours of the night; the day had a total of 24 hours including 12 hours for the day, 1 hour for sunset, and 1 hour for sunrise. Merkhets were used to replace sundials, which were useless during the dark.
Astronomical rings, also known as Gemma's rings, are an early astronomical instrument. The instrument consists of three rings, representing the celestial equator, declination, and the meridian.
The Gnomon of Saint-Sulpice is an astronomical measurement device located in the Church of Saint-Sulpice in Paris, France. It is a gnomon, a device designed to cast a shadow on the ground in order to determine the position of the sun in the sky. In early modern times, other gnomons were also built in several Italian and French churches in order to better calculate astronomical events. Those churches are Santa Maria del Fiore in Florence, San Petronio in Bologna, and the Church of the Certosa in Rome. These gnomons ultimately fell into disuse with the advent of powerful telescopes.
A sundial is a device that indicates time by using a light spot or shadow cast by the position of the Sun on a reference scale. As the Earth turns on its polar axis, the sun appears to cross the sky from east to west, rising at sun-rise from beneath the horizon to a zenith at mid-day and falling again behind the horizon at sunset. Both the azimuth (direction) and the altitude (height) can be used to create time measuring devices. Sundials have been invented independently in every major culture and became more accurate and sophisticated as the culture developed.
The Whitehurst & Son sundial was produced in Derby in 1812 by the nephew of John Whitehurst. It is a fine example of a precision sundial telling local apparent time with a scale to convert this to local mean time, and is accurate to the nearest minute. The sundial is now housed in the Derby Museum and Art Gallery.
A clock position, or clock bearing, is the direction of an object observed from a vehicle, typically a vessel or an aircraft, relative to the orientation of the vehicle to the observer. The vehicle must be considered to have a front, a back, a left side and a right side. These quarters may have specialized names, such as bow and stern for a vessel, or nose and tail for an aircraft. The observer then measures or observes the angle made by the intersection of the line of sight to the longitudinal axis, the dimension of length, of the vessel, using the clock analogy.
In Roman timekeeping, a day was divided into periods according to the available technology. Initially, the day was divided into two parts: the ante meridiem and the post meridiem. With the introduction of the Greek sundial to Rome from the Samnites circa 293 BC, the period of the natural day from sunrise to sunset was divided into twelve hours.
A tide dial, also known as a mass dial or a scratch dial, is a sundial marked with the canonical hours rather than or in addition to the standard hours of daylight. Such sundials were particularly common between the 7th and 14th centuries in Europe, at which point they began to be replaced by mechanical clocks. There are more than 3,000 surviving tide dials in England and at least 1,500 in France.
This timeline of time measurement inventions is a chronological list of particularly important or significant technological inventions relating to timekeeping devices and their inventors, where known.
An equinoctial hour is one of the 24 equal parts of the full day.
