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How sundials work -

Sundials are designed with two parts: a surface known as a "dial face," and a usually-inclined "gnomon" that casts a shadow on the dial surface. As the sun moves, the gnomon’s shadow aligns with different hour-lines marked on the dial face.

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The Hemispheres -

In the Southern Hemisphere, a sundial’s gnomon typically faces South, while the Northern Hemisphere will have it point to the North. The hours on the dial face also read in opposite directions: clockwise in the Northern Hemisphere, and counterclockwise in the Southern.

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Around the world in 3,000 years -

Sundials were independently invented by every major culture around the world. It is clear that, even more than three millennia ago, humans were more alike each other than they could ever imagine.

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The first sundial -

Archaeologists and anthropologists have noted that the first device most likely used for telling time was the vertical gnomon, pictured here. The device dates back to about 3500 BCE, and it consisted of a vertical stick or pillar that cast a shadow on the ground and indicated the time of day depending on its position in the sky. This is the early blueprint of what is known as the sundial.

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Pharaohs and their clocks -

Ancient Egyptian astronomy indicates that "shadow clocks" came into existence around 1500 BCE. The world’s oldest known sundial (pictured) was discovered in Egypt’s Valley of the Kings. Ancient sundials dating to this period have also been discovered in modern Russia.

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Time is like water -

Sundials were not the only timekeeping devices in ancient Egypt. Water clocks were also used during this period. The Chinese even resorted to using incense clocks (pictured) by the 6th century.

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The hemicycle -

The Greek astronomer Aristarchus of Samos invented the hemispherical sundial, or hemicycle, in about 280 BCE. It was made from a wood or stone cubical block with a pointer fixed at the center. As the sun moved through the sky, the pointer’s shadow was, approximately, a circular arc.

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The four seasons -

Each season called for a variation in the length and position of a hemicycle’s arc, since the sun’s trajectory always changes by the season. Each seasonal arc had 12 equal divisions, which meant that each day was divided into 12 equal parts, or "hours." Naturally, this meant that some seasons had longer hours than others.

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Sundials without borders -

According to records from the Arab astronomer al-Battānī, the hemicycle was still largely in use in Muslim countries during the 10th century.

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Prayers and sundials -

Medieval Muslims were particularly interested in sundials, since they allowed them to keep track of the correct times for prayer. In fact, Muslim sundials often had lines that indicated prayer times, with some sundials having no other lines at all.

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A Tunisian courtyard -

As an example, the Great Mosque of Kairouan in Tunisia has a sundial in its courtyard that was built in the 7th century CE and determines the time for prayers.

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Tower of the Winds -

The hemicycle wasn’t the last time that the Greeks played around with sundials and their complexity. By 100 BCE, they had already constructed the Tower of the Winds in Athens, which has eight planar sundials oriented toward different compass cardinal points.

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A sundial variant -

In about 290 BCE, the Babylonian astronomer Berosus created a variant of the Greek sundial by cutting away part of the hemicycle’s arc.

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The conquest of the Romans -

Much like the Greeks, the Romans also used seasonal arcs in their sundials. The empire’s first sundial was captured from the Samnites and installed in Rome circa 290 BCE, but they designed their own sundial for the city only 130 years later.

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Vitruvius and the Man -

Interestingly, the Roman architect Vitruvius was responsible for naming many sundials during the 1st century BCE. On another note, Vitruvius’ discussions about the human body ultimately led to Leonardo da Vinci’s famous drawing of the 'Vitruvian Man.'

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Is it a bird? Is it an obelisk? -

In about 10 BCE, the Romans built the Solarium Augusti, which is a classic obelisk that acts as a large gnomon for a sundial. The obelisk can still be seen in Rome.

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The lonely sundial - The ruins of Pompeii are home to a sundial that survived the eruption of Mount Vesuvius in 79 CE. This design is based on the Babylonian variant of the Greek sundial.

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The rise of mechanization -

Mechanical clocks came into existence in Europe in the 14th century, but sundials were still used to reset these clocks. Pendulum clocks were invented in the middle of the 17th century, which allowed for near-perfect timekeeping.

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Better than the Earth -

An electrical-driven pendulum clock, named the Shortt–Synchronome clock, was designed in 1921 and was the first clock to be more accurate at timekeeping than the Earth itself.

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Wait and watch -

The 16th century saw the invention of the first wristwatches. In the military, watches were considered to be valuable tools, especially in the Franco-Prussian War (1870–1871).

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Italian time -

Although mechanical clocks were making an appearance, sundials were not quite out of fashion yet. In Italy, Francesco Bianchini designed the Clementine Sundial, which was installed in the Basilica of Saint Mary of the Angels in Rome and inaugurated in 1702. The sundial was named after Pope Clement XI, who requested the sundial’s design.

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How is a building like a sundial? -

In the early 18th century, the Giant Sundial of Jantar Mantar in Jaipur, India, was constructed. The sundial stands 27-m (88.5-ft) tall, and its shadow moves visibly at 1 mm per second.

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The chronometer -

Following the invention of the pendulum clock, the early 1700s saw the invention of the marine chronometer, used primarily in ships.

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Electric clocks -

English inventor Francis Ronalds was the forerunner for the production of the electric clock in the early 1800s, which was powered by high voltage batteries known as dry piles. This invention proved far more reliable than previous timekeeping devices.

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Obsolescence -

The Age of Industrialization inevitably favored mechanical clocks over the sundial, but that hasn’t stopped people from being continually fascinated with these devices. For instance, a modern equinoctial sundial, named ‘Timepiece’ was installed in London in 1973. Sundials have more frequently become architectural and design statements rather than used for their intended purpose.

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Sundial Bridge -

In 2004, the American city of Redding finished construction of Sundial Bridge. The support tower of the bridge forms a large gnomon, which points due north.

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A Millennium celebration -

Another modern inclusion is the Perranporth Public Sundial in Cornwall, England. It was constructed as part of the United Kingdom’s Millennium celebrations in 2000.

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The French polar sundial -

The country of France has their own addition to this list, with a cylindrical polar sundial designed by Jean Raffegeau. It's found in Roussillon, Vaucluse.

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Clocks made of stone -

Interestingly, there are a plethora of other man-made constructions that do not follow our conventional understanding of the sundial. For instance, Stonehenge has been a large sundial for almost 4,000 years, even though it wasn’t constructed for that purpose. It marks the longest and shortest days of the year, simply through the arrangement of the stones.

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Atomic clocks -

The most practical timekeeping devices that are used today are atomic clocks. They can accurately keep time within a few seconds over many thousands of years. As such, they are primarily used to calibrate other clocks, much in the same way that sundials were used to keep time in pendulums.

Source: (Britannica) (The British Sundial Society) (Guilford Press) (Routledge)

See also: The UK and Ireland's most fascinating Neolithic sites

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