Before alarm clocks, people relied more heavily on their circadian rhythms, humans hired to wake them, and on tools such as candle clocks that dropped pins in metal trays at roughly set intervals.

A 2,000-year history of alarm clocks

Clocks have revolutionized the way we live, structuring our days into abstract, regular units and providing quantification for those who are chronically late. The alarm clock was the next obvious step: clocks which not only tell you the time but...

Early timekeeping tools included sundials, water clocks, and astrolabes

Astrolabes also provided a person's latitude based on the height of the stars in the sky, thus aiding in navigation. Incense and candle clocks relied on the constant burning rate of fire to track the passage of time based on premarked locations with equal-interval spacing.

Chronobiologists study the effect of time on biological cycles

Circadian rhythms were first observed in the 1700s, when French astronomer Jean-Jacques D'Ortous de Mairan put a plant in a dark room and watched it still respond to day and night cycles, setting off further studies about specific light-dark biological cycles, an area of inquiry that continues today with the human "clock proteins" at the molecular level.

The lost medieval habit of 'two sleeps'

While most people accept a single seven-to-nine-hour nightly slumber is ideal, the approach is a relatively modern idea. For centuries, interrupted sleep was the norm, with historians uncovering descriptions of two periods of sleep during the normal 24-hour cycle.

Why atoms are used to keep track of time and define the meaning of a second

Small variations in the production of human-made devices, such as mechanical watches and pendulums, make them unreliable for the ultraprecise timekeeping required by modern technology, including financial transaction timestamping and GPS. Because atoms obey fundamental laws of nature and never wear out, their light emissions when energized provide a consistent timekeeping signal.

Circadian rhythms shift as we age—making older adults want to go to bed earlier

Throughout our lives our internal biological clocks shift. Early-to-rise toddlers become hard-to-wake teens and eventually early-to-sleep seniors. Circadian rhythm fluctuations throughout our life cycle explain some of these changes.

There is a best way to wake up—but not a best time

Sleep and circadian rhythm researchers say that waking up at a consistent time each day—even on weekends—and viewing morning sunlight are the best ways to keep body functions running at their peak. (Some users may encounter a paywall.)

The hour originated from an ancient Egyptian astronomical system

The movements of astronomical objects, measured in a day and a year, form the foundation of our sense of time. The Egyptians divided each day and night into 12 time eras, using arbitrarily selected stars as references rather than movements of specific celestial objects.

Rather than measuring the rising and falling of the sun or pendulum swings, optical clocks track the passage of time using the extremely consistent vibrations of atoms.

The frequency of visible light is significantly greater than that of microwaves used in cesium atomic clocks. This makes optical clocks about 100 times more accurate, losing at most one second across the entire age of the universe.

Studies suggest when you sleep is as important as how much you get.

The earliest earthquake-detection device—the seismoscope—was invented in China in 132 CE and featured eight ball-wielding dragons facing different directions.

From the Greek for 'star taker,' the astrolabe allowed individuals to tell time and determine their latitude based on the position of the sun or other stars, as well as calculate the height of objects.

Artificial lighting and modern practices like working late are linked with sleep shifts

An analysis of five adults participating in a German reality program that tasked them with living in a Stone-Age-like settlement for 2.5 months, provided some insights into how modern conditions may have shifted our circadian rhythms. The participants slept about 90 minutes more under these conditions, and went to bed earlier and rose earlier, raising questions about how circadian rhythms, sleep, and sleep quality are affected by modern lifestyles.

'Zeitgebers' like light are external cues for the circadian clock

German for "time giver" or "time cues," common external zeitgebers include sunlight, food, and physical activity. The timing of these external influences can shift circadian clocks or lead to irregularities: A 2018 study, for example, found that later light exposure and meals were linked to later timing of peak activity and bedtimes.

The New Year's ball was based on a navigational tool

Robert Wauchope, a member of the Royal Navy, developed the contraption in 1818 so crews could know the time while out at sea. The ball would descend at the same time every day, allowing ships to set their clocks accordingly.

Mechanical watches measure the passage of time via the vibration of a quartz crystal

When electricity from a battery passes through the crystal inside a watch, the crystal vibrates, creating an electrical signal with a precise frequency of one vibration per second. This signal moves the hand of the watch so that it ticks once per second, allowing it to track the passage of time.

The Antikythera mechanism: The oldest-known analog computer

A device now considered the world's oldest computer was pulled from a shipwreck more than 120 years ago. Known as the "Antikythera Mechanism," it is now believed to have allowed precise tracking of astronomical positions, and its sophistication overturned understanding of Ancient Greek capabilities.

A history of raising the alarm, from rattles to 911

Because fires spread so quickly, communities around the world have deployed many tactics to raise the alarm to get help. This history from the Museum of Natural History dives into the use of rattles, bells, and brigades to gather help to fight fires, showing just how far we've come since 911 was introduced in 1968.

Researchers once thought Stonehenge functioned as a precise astronomical computer

In the 1960s, scientists used early computers to analyze the stone layout at Stonehenge, arguing it could predict eclipses and other celestial events. This BBC Sky at Night Magazine piece explains how the theory arose—and why scholars now doubt it.

Parasites have circadian rhythms, too

Researchers are working to unravel how circadian rhythms of parasites and their hosts affect one another. They’re investigating how to potentially target and disrupt those clocks for disease treatments.

The first commercially successful calculating machine—the arithmometer—was patented in 1820 but not mass-produced for over three decades, likely because its inventor was focused on his insurance business.

How atomic clocks have been used to measure the universe's fundamental constants

Atoms behave according to a set of parameters that scientists have determined give reality its properties. For example, the fine-structure constant, α, quantifies the strength of interactions between charged particles. Since the light emitted by atoms as they move between energy levels is affected by α, analyzing these emissions—the basis of atomic clocks—using different atoms helps calculate α.

Single-cell organisms have circadian clocks that direct daily biochemical routines

Cyanobacteria, a type of light-sensitive bacteria, use this clock to signal when to alternate between making organic compounds through photosynthesis and when to convert atmospheric nitrogen into usable ammonia. Upregulating photosynthetic machinery before dawn helps ensure efficient photosynthesis.

Dragon seismometers, Baghdad batteries, and more ancient artifacts

The ancients were behind us in many ways, but some inventions from the time have not been surpassed in the modern era in effectiveness, beauty, or cleverness. This quick list of bizarre ancient inventions includes a battery from Baghdad, a Molotov cocktail-like explosive in Greece, and more.

Railroads and long-distance communication led to the development of time zones, with Greenwich established as the prime meridian—the longitude of 0 degrees—due to British advancements in star mapping and navigation.

What the stars once meant to ordinary people

The stars were a crucial aid for ordinary human beings in premodern societies, acting as regular timekeeping phenomena and celestial navigators. Today, light pollution and modern technology have rendered the stars a mere aesthetic delight for most of us, but their significance in history remains. Watch this brief video to learn how premodern humans used the stars for navigation, mathematics, and more.

At the age of seven, Grace Hopper dismantled alarm clocks

Foreshadowing a career in computers, Hopper exhibited a curiosity for gadgets at a young age and took apart seven clocks, determined to understand how they worked. Despite having a dollhouse, Hopper built an elevator for it and showed a greater interest in building toy furniture than playing with dolls.

Learn more about the history of fireworks, which date back to an accidental invention during an alchemist's quest for information about immortality.

The first printed Advent calendars were from Germany in the early 1900s

Printed Advent calendars originated in early-20th-century Germany, where printer Gerhard Lang created the first commercially produced versions. Inspired by his mother’s homemade countdowns, Lang added small doors in the 1920s, establishing the format that spread worldwide.

The body's sleep-wake cycle is one of its many circadian rhythms

The body's sleep-wake cycle is one of its many circadian rhythms, which are behaviors or biological processes that exhibit 24-hour patterns. These rhythms are deeply impacted by light exposure, food availability, and much more, meaning where you live impacts your sleep.

More than 2,000 years ago, a hand-powered model of the solar system called the Antikythera mechanism—the oldest example of an analog computer—could predict solar eclipses.

The extreme precision of atomic clocks highlights gravitational time dilation

Scientists at the National Institute of Standards and Technology have constructed clocks made out of stacked strontium atoms, which show differences in the passage of time across just a millimeter of height consistent with predictions from general relativity, where atoms closer to Earth's center tick off time more slowly.

Before electric lights, Christmas trees were lit with real candles

The practice of lighting Christmas trees with electricity didn’t begin until the late 1800s. Before that, families used wax candles on branches—a dangerous tradition that originated in 16th-century Germany.

The Middle Ages produced inventions that still affect our lives today, like coffee houses and improved agricultural techniques.

The earliest record of dream interpretation dates to Ancient Sumer, an analysis of a Sumerian priest king's dream around 2700 BCE.

One of the first mechanical calculators—the Pascaline—was built in the 1640s by French mathematician Blaise Pascal to help his father, who worked as a tax collector.

What did people do before eyeglasses were invented?

An estimated two-thirds of the world's adults use a form of prescription glasses or contacts, proof spectacles were a godsend when they were invented in 1286 CE. But what did people do before that? Different tools were used for distinct vision problems, but some would use magnifying lenses, clear emeralds, and more. Watch this video for a historical explanation.