Time zones were established in the 1880s because of railroads, which suffered from scheduling problems due to each town managing its own timekeeping.

In contrast to telling time by physical signs like the sun or stars, cultural time relies on political agreement and standards. The convention of time zones arose due to transportation and communication advancements, and while many work just fine, some are pretty wild. Chief among those is the time zone of the uninhabited Baker and Howland Islands in the central Pacific, which results in a technical 26-hour day.

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.

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.

The site displays the current time across all American time zones—corrected for network delay—and shows whether your device's clock has drifted. Computer clocks rely on quartz crystals that drift slightly with temperature and age, requiring alignment with atomic clocks (which are so stable that seconds are defined by them).

Because Earth exerts a stronger gravitational pull than the moon, it lags behind between 56 and 59 microseconds each day, or about one second every 46.5 years. This impacts essential synchronous operations of future electronic equipment on the lunar surface, which could be alleviated by a standardized conversion system between Earth and moon time zones.

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.

Messing with the amount of daylight each day has consequences, as America found out in 1974 when it first passed all-year daylight saving time. See why it was revoked less than a year later.

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.

Benjamin Franklin did not invent daylight saving time. But while living in Paris, he did pen a satirical letter to Parisians suggesting they could save money on lamp oil by changing their sleep schedules. Read it in full here.

Daylight saving time is supposed to help—but does it? Dive into the history, science, and consequences of this biannual aspect of American life (unless you're from Arizona or Hawaii).

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...

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 first map to use latitude and longitude positions was created by Ptolemy in 150 CE, over 700 years after the oldest known world map, the Imago Mundi, was made with a Babylonian clay tablet. The Spanish crown created a secret master map from hundreds of sailors’ reports.

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.

Time travel has fascinated humans for centuries. It appears in myths, literature, and science fiction. One of the earliest examples comes from the 400 BCE Hindu epic Mahabharata, describing time dilation long before Einstein’s Theory of Relativity. By the 19th century, stories introduced machines enabling time travel—setting the stage for modern sci-fi.

Due to differences in where objects are located within gravitational fields, time will run at different rates, which has major impacts on technology that relies on synchronization. For example, GPS satellites run about 38 microseconds faster every day than clocks on Earth's surface, resulting in GPS discrepancies of about six miles, were it not for software corrections.

A 2025 study that examined time changes found that permanently changing to standard time would slightly reduce obesity and stroke risk more than switching to permanent daylight saving time.

Changing clocks twice a year disrupts circadian rhythms, which last an average of 24 hours and 12 minutes. Studies have shown that permanent daylight saving time provides fewer health benefits than standard time.

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.

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.

Humans have been captivated by the prospect of leaping forward and backward in time for thousands of years. Georgia Institute of Technology Science Fiction Studies Professor Lisa Yaszek recounts how the concept has been utilized by storytellers from 400 BCE to modern-day to explore our relationship with the supernatural, technology, and the past. In a way, this historical recounting is a journey through time.

About seven base units, such as meters for length, have historically been used to describe everything in our physical reality. However, researchers have shown that, through relativistic space-time, clocks can serve as replacements for rulers, scales, and other instruments, allowing everything to be measured in terms of time.

In the early 1800s, bonds were used to fund US railroads and canals in Great Britain. “Liberty Bonds” were sold during both World Wars in the 20th century. Learning about the early and modern history of bonds can offer a glimpse into how the modern bond market came to be.

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.

Covering over 8,000 miles, William Clark’s maps charted rivers, mountains, and tribal territories with remarkable accuracy. Equipped with sextants, compasses, telescopes, and more, Clark became an expert at surveying—requiring extensive celestial and topographical observations each day.

The omnibus, a large horse-drawn stagecoach that ran a fixed route and carried a dozen riders at an affordable fare, was different from a private carriage because it carried everyone, not just the wealthy.

For many centuries, during which China was an imperial nation, the lunar/lunisolar calendar (aka the “rural calendar”) was the basis for organizing the year. Several attempts were made over the decades to switch to the Gregorian calendar—which begins Jan. 1—but it wasn’t until the People’s Republic of China was founded in 1949 that it stuck.

Before the telephone was invented in the mid 1800s, people had to trade stocks in person. But once office telephones and computers became commonplace, banks and other financial institutions didn't necessarily need to have their headquarters near exchanges like Wall Street's New York Stock Exchange.

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.

Want to see how Wall Street (and New York City as a whole) has changed over time? Use this timeline and map to see Manhattan today overlaid with the precise boundaries of early land grants to the Dutch in the 1600s. Scroll through the progress of city building through the first century of European settlement there.

Until that time, each banker was required to bring that day's checks to every other bank for settlement. Perhaps understandably, the first place bankers opted to gather to clear and settle checks was a tavern known as the Five Bells. The innovation gave rise to what would become clearinghouses, key institutions that facilitate payments.

During “Railway Mania,” speculative excitement pushed British rail shares to extreme valuations as investors chased rapid expansion. When costs ballooned and profits failed to materialize, the bubble collapsed in 1847—wiping out fortunes across the country.

While a prisoner of war for four years during World War II, the Japanese military confiscated Ned's watch, so he built sundials to keep track of time. Ned would later research and write a book on sundials and be honored with a lifetime membership to the North American Sundial Society.