The concept of measuring time emerged around 5,000 to 6,000 years ago when humans began settling down and building civilizations. Prior to that, time was only divided into two concepts: day and night. The brilliant scientist Einstein once said: “The distinction between past, present, and future is only a stubbornly persistent illusion.”
Regardless of whether time is real or not, measuring this concept has become indispensable in our lives. Humans have created various methods to define this quantity, from the most rudimentary way of tracking the movement of the sun to the ultra-precise atomic clocks of today.
Let’s take a look at some time-measuring methods that humans have used throughout history, as highlighted by Discovery magazine.
Based on the Sun
Sundial.
The Egyptians were likely the first to turn timekeeping into a science. They constructed large obelisks as early as 3,500 BC and positioned them strategically to measure their shadows. Sundials operate on the principle of tracking the shadow cast by a stick placed on a stone slab as it changes direction and length. Initially, this tool only helped them identify midday, but over time, they devised methods to subdivide time into smaller parts.
Two thousand years later, the Egyptians also studied and created the first sundial designed into ten segments. This sundial operated based on the sun’s movement. The raised part of its face would cast a shadow on the dial face, pointing to a marked number. At noon, the sundial had to be rotated 180 degrees to continue indicating the afternoon hour. Naturally, this sundial could not tell time on cloudy days or at night. It was also inaccurate because the sun is at different angles at various times of the year; hours could be shorter or longer depending on the season. Nonetheless, by 30 BC, over 30 types of sundials were in use in Greece, Italy, and Asia Minor. Today, our timekeeping system still relies on the sun through established time zones.
Based on the Stars
The Egyptian astronomical instrument “merkhet.”
The Egyptians also invented a method for timekeeping at night using an astronomical instrument called merkhet around 600 BC. This device consisted of a cord with a weight on one end used to measure a straight line. Astronomers of that time aligned two merkhets towards the North Star and used them to mark a north-south line, also known as the celestial meridian, in the night sky. Time would be determined when certain stars crossed this line.
Hourglass
An intricately crafted medieval hourglass.
An hourglass is a timekeeping device consisting of two glass bulbs connected by a narrow neck, allowing fine sand to flow from one bulb to the other at a constant rate. When the sand from one bulb has completely flowed into the other, the hourglass is turned upside down to allow the sand to flow back. Factors affecting the sand’s flow time include the amount of sand, the size and angle of the bulbs, the width of the neck, and the quality of the sand.
The origin of this type of clock is still uncertain. Some sources claim that it was invented by a French monk named Luitprand in the 8th century; however, it wasn’t until the 14th century that this type of clock became widely popular. Hourglasses were designed to measure various short intervals of time: some for 1 hour, half an hour, or even just a few minutes. In the past, wealthy individuals often displayed large hourglasses as home decor, but over time, this type of clock became common across all social classes. Today, the most commonly found hourglasses are used as souvenirs, typically measuring just 3 minutes for timing boiled eggs.
Water Clock
A sample of a water clock.
This is the first timekeeping device that does not depend on astronomical factors to measure time, meaning it can be used at any time of day or night. The water clock operates by measuring the flow of water from one container to another. The Egyptians invented this device; however, it became popular and was widely used around the world, with some countries continuing to utilize this time-measurement method until the 20th century.
Mechanical Clock
The mechanical clock was developed in Europe in the 1300s. It operates on a system of weights combined with a pendulum. The earliest clocks did not have hour or minute hands but indicated the hour by ringing (the English word “clock” comes from the French “cloche,” meaning “bell”). The mainspring system was developed in the 15th century. The minute hand appeared in 1475, and the second hand emerged around 1560 (although it was not very accurate and only indicated that the clock was still running). In 1653, Galileo Galilei invented the pendulum, leading to the creation of the pendulum clock by Christiaan Huygens. He discovered that if the pendulum was 99.38 cm long, one cycle would be exactly 1 second. In 1670, William Clement invented the anchor escapement system, which improved the accuracy of clocks. From then on, minute and second hands became standard in most clocks.
Unique Clocks
Chinese incense clock.
Centuries ago, various methods for measuring time were devised. The Chinese invented a method of timekeeping using incense between 960 and 1270, and this method became widespread throughout East Asia. This clock consists of metal balls tied along an incense stick at equal intervals by cords; when the incense burns down a certain length, the cords will slip, and the balls will fall, creating a sound to signal the hour.
Candle clocks have marks on the body of the candle; as the candle burns down, it indicates the corresponding time marked on the body. Sometimes there are no markings on the candle, and users must know the burn time to estimate the time accurately.
Quartz Clock
The structure of a quartz clock.
In 1880, Jacques and Pierre Curie discovered the piezoelectric effect in quartz crystals; this means they can convert mechanical vibrations into electrical pulses and vice versa. This discovery led to the realization that quartz could create very stable electrical oscillations as a standard, paving the way for quartz clocks, which are more accurate and convenient than pendulum clocks. For the first time, Walter G. Cady applied quartz in an electronic oscillator control circuit in 1921. He published the results in 1922, and by 1927, Warren A. Marrison had applied quartz crystals to control the operation of clocks.
This type of clock has several advantages: convenient, no winding needed, multifunctional, and stylish… Therefore, it is very popular among young people. Currently, there are three types of quartz clocks available: digital quartz clocks, quartz clocks with hands, and hybrid digital-hand clocks.
Atomic Clock
The world’s first atomic clock (1949)
An atomic clock is a timekeeping device that regulates time based on the oscillation state of atoms. The oscillation frequency of atoms is constant and measurable, making atomic clocks the most accurate type of clock to date.
In 1949, the first atomic clock operating on the motion of ammonia molecules was constructed at the National Institute of Standards and Technology in the United States.
In 1955, Louis Essen successfully developed the atomic clock based on the atomic movement of Cesium at the National Physical Laboratory in the United Kingdom.
In addition to Cesium atoms, Rubidium, Hydrogen, and other atoms or molecules have also been successfully utilized, achieving increasingly higher accuracy.
Atomic clocks are used for precise time measurement, determining and coordinating time zones and various time systems with one another. Furthermore, atomic clocks are utilized in rockets, drones, and particularly for measuring time to determine distances on satellites in positioning systems such as GPS, GLONASS, or Galileo.
Calendar
Mayan Calendar
The solar calendar is based on observable seasonal changes, synchronized with the apparent motion of the Sun.
The most basic use of a calendar is to determine dates: to announce future events and record past occurrences. Dates may hold significance for regular seasons, religious observances, or social holidays. For instance, a calendar provides a method for identifying which days are religious holidays or public holidays, which days mark the beginning or end of production and business cycles, as well as which days hold legal significance, such as expiration dates in contracts or tax due dates. Some calendars also provide additional useful information, such as details about specific days or seasons.
