Got a Sec? Take This Quiz on the History of Timekeeping

Tall pendulum clocks powered by the force of gravity are known as grandfather clocks. The name comes from “My Grandfather’s Clock,” a popular 1876 song by American songwriter Henry Clay Work. However, its name is apropos, as grandfather clocks were some of the first mechanical clocks ever made.

The canonical hours represent the seven prayers that Christians may recite throughout the day. Matins is the lengthiest hour and originally was recited at night. (Now, the prayers are said at any time of the day.) Lauds is a solemn morning prayer, and vespers is the evening prayer. Before the advent of mechanical clocks, canonical hours were important because churches would ring their bells to mark these moments of prayer.

A clepsydra, also known as a water clock, measured time using the flow of water. This was especially useful when other timekeeping implements, such as the sundial, couldn’t keep time at night. The invention dates back to the 14th century BCE in Egypt and was used as late as the 16th century CE. Galileo, for example, used a mercury-filled clepsydra to time the movement of planets and moons.

Although horologists aren't 100% certain of the cuckoo clock’s origin, the timepiece was likely created in the Black Forest region of Germany in the 17th century. The cuckoo is thought to have been chosen because the bird was already a timekeeper of sorts, as its call was considered a harbinger of spring.

Before King Numa Pompilius, the Roman calendar was a mess. First instituted by Romulus, the mythical founder of Rome, the early calendar was only 304 days long, contained only 10 months, and started in March. To better align things, Pompilius created the 12-month calendar. Although it wasn’t perfect, the new calendar was a vast improvement over the one that came before it.

While time always moves forward, the flow of time is relative to your location. For example, time flows differently on the surface of Earth than in the planet’s orbit. Albert Einstein detailed this notion in his theory of general relativity. The difference is only seven-millionths of a second per day, but these tiny fluctuations are immensely important for satellites. In fact, GPS wouldn’t exist without Einstein’s theory baked into the satellite network’s design.

In William Shakespeare’s play “Julius Caesar,” the titular character is warned to “beware the ides of March,” otherwise known as March 15. “Ides,” along with other terms such as “kalends” and “nones,” referred to days on the lunar-based Roman calendar. “Ides” meant the middle of the month, while “kalends” marked the new moon and “nones” denoted the quarter moon.

The Babylonians popularized the base-60 numerical system, also known as the sexagesimal, which was based on the highly divisible number 60. The system divided a year into 360 days, organized hours and seconds into increments of 60, defined a circle as 360 degrees, and more. While much of the world eventually switched to a numerical system based on the number 10, remnants of base-60 live on in the way we tell time today.

Called the “Magic Eye,” the photo-finish timekeeping technology was created by the watch company Omega, and debuted at the 1948 Summer Olympics in London. The Magic Eye used photoelectric cells to record the exact moment the finish line was crossed. Although it was only supposed to be on hand as a backup, the technology immediately proved its worth when judges used it to determine the winner of the men’s 100-meter sprint.

Mechanical clocks were used throughout Europe for at least two centuries before Galileo Galilei came along, but the Florentine astronomer (1564-1642)drew up a theoretical method in which a pendulum could regulate a clock’s ticking mechanism, making it much more accurate. The first working pendulum clock was constructed in 1656, by Dutch mathematician and astronomer Christiaan Huygens.

In 1967, scientists changed the official definition of a second from 1/86400th of a day to “the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.” This is the basic principle behind atomic clocks, which use the resonance frequencies of atoms to measure time with unprecedented accuracy. Some atomic clocks are so accurate that they won’t lose a second in 15 billion years.

Although counterintuitive, “UTC” stands for “coordinated universal time” in an effort to not favor any particular language and also to align with the already-established abbreviation “UT” for “universal time.” Originally conceived in the late 1800s for standardizing rail and shipping schedules, UTC sets the time for all time zones in the world, and NASA uses the standard for its spacefaring missions.

Most months on the calendar were named after Roman gods or numbers. However, July and August were named after two important figures of Roman history: Julius Caesar and Emperor Augustus. The months were originally named “Quintilus” and “Sextilius,” meaning “fifth” and “sixth” in Latin, respectively. They earned their new monikers in the first century BCE.

Although some women wore watchfaces on bracelets in the early 20th century, soldiers were the first to strap the timekeeping devices to their wrists. With the onset of World War I, watches transitioned from a fashion accessory to a military tool when aviators and soldiers used them to time assaults. After that, the wristwatch became a must-have timekeeping accessory.

The Chinese lunar calendar, which begins on the new moon between January 21 and February 20 each year, has been in use since its creation in 2637 BCE by the first Chinese emperor, Huangdi, also known as the Yellow Emperor. The months of the lunar calendar are designated by animals of the Chinese zodiac, such as the dog, pig, and dragon — but the cat is not among them.

In 45 BCE, Julius Caesar, the de facto ruler of the Roman Republic, instituted a new timekeeping system, the Julian calendar, in an effort to more effectively rule his expanding domain. The calendar, which measured a year as 365.25 days, lasted for more than 1,500 years before slight astronomical errors forced the creation of today’s Gregorian calendar.

Before the clever engineering of water clocks (dating as far back as 1500 BCE) or the popular incense clocks of China’s Song dynasty (960-1279 CE), ancient civilizations relied on the trusty sundial to tell time. Sundials, also known as shadow clocks, date back to at least 3500 BCE to Mesopotamia and ancient Egypt, and were later improved upon by the ancient Greeks, Romans, and Islamic scientists in the Middle Ages.

“A.M.” is an abbreviation for the Latin term "ante meridiem," signifying “before noon.” “P.M.” means "post meridiem," Latin for “after noon.” According to the Physical Measurement Laboratory, which is part of the U.S. Department of Commerce's National Institute of Standards and Technology, "12 a.m. and 12 p.m. are ambiguous and should not be used." They recommend opting for the terms "noon" and "midnight" instead.

Most of Europe observed the Julian calendar for around 1,500 years, but small mathematical inaccuracies exacerbated across many centuries eventually misaligned the calendar dates with astronomical reality. For one, Easter, Catholicism's holiest day, which was traditionally observed on the spring equinox, became 10 days out of sync. To correct the errors, Pope Gregory XIII decided to make a few adjustments, creating today’s modern calendar.

Built by Neolithic druids some 5,000 years ago, Stonehenge is a cosmic clock that tracks the summer and winter solstices, which was important not only for planting crops, but also for the religious practices of Celtic pagans. Experts believe that the famous monument possibly tracked solar and lunar eclipses as well.