The hour originated from an ancient Egyptian astronomical system

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.

Meet Hipparchus, the Greek astronomer who created the world's first star map

Astronomer Hipparchus created accurate maps of the night sky way ahead of his time, with coordinates sometimes within a single degree of modern values. Hipparchus founded a new theory of star motion, modeling the sky as a celestial sphere with coordinates similar to latitude and longitude—concepts only recently created in Hipparchus' time.

Railroads and long-distance communication led to the development of time zones

Noon had been determined independently at each location based on when the sun was highest in the sky, but this became impractical for standardizing transportation. British star-mapping and navigation advancements established Greenwich as the prime meridian through Greenwich Mean Time, or GMT.

Earth's circumference was estimated over 2,000 years ago using geometry and shadows

By measuring the angle of the shadow cast in Syene when no shadow was cast in Alexandria, Eratosthenes used the distance between the two cities and trigonometry to estimate the Earth's circumference to within a few percentage points of the actual value.

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...

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.

For centuries, it was common to sleep in two shifts: a few hours at the beginning of the night, and a longer period beginning around midnight

The ancient Roman origins of the leap year

The earth's orbit around the sun takes about 365.2422 days, leaving farmer almanacs the awful job of pretending the calendar year fits into a whole number. This article explores the modern origins of the civil solar calendar and its leap year. The Julian calendar, named after the Roman emperor Julius Caesar, cut the calendar year into 365.25 days, gifting the public an extra day every four years. Learn more of the history here.

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.

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.

Ancient civilizations predicted eclipses by tracking different cycles of their recurrence

The periodic nature of the orbits of the sun, moon, and Earth results in several series called saros cycles, in which the geometric configuration of these celestial bodies that produces an eclipse recurs after about 6585 days. Because eclipses are viewable from different locations on Earth, there exist many saros cycles, one for each ecliptic configuration.

New Year's Eve celebrations date back to ancient Babylon

Rather than celebrating in winter, the Babylonians honored the vernal equinox, a day in late March with equal amounts of darkness and light that signaled the start of a new year. They celebrated with Akitu, an 11-day festival.

Earth’s tilt and orbit cause the sun to create a figure-eight pattern

The shape—called an analemma—can be obtained by photographing the sun from the same location and time daily for a year. The Earth's eccentricity created the analemma's width, and its tilt shifts the sun's height in the sky over the seasons.

The essential facts to know about ancient Egypt

Ancient Egypt spanned three millennia—more than 10 times the history of the US—but disappeared from the world's consciousness until the 18th century when it was rediscovered by Napoleon's army. Take a trip through the dynastic periods in this three-minute video.

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.

The earliest mention of time travel

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.

The Ishango bone suggests mathematics was born about 20,000 years ago

Ancient civilizations developed mathematical systems for various purposes, including the Egyptians for the construction of the pyramids and the Ancient Greeks for logical reasoning in theorems. However, these systems were predated by the Ishango bone—found in the Democratic Republic of the Congo—whose notches suggest a base ten system, prime numbers, and simple mathematical operations.

Learn how the Egyptians, Romans, and other ancient civilizations worshipped the sun

In Egypt, the pharaoh was seen as the living embodiment of the son of Ra, the sun god. In Mesopotamia, the sun god Shamash was a divine judge whose light could reveal the truth. Huitzilopochtli, the Aztec god of sun and war, was thought to require sacrifices to prevent the universe's destruction.

Explore how far you've traveled through space while living on Earth

Using the "Cosmic Odometer," users can enter their birthday and learn how far they have moved through space due to the combined effects of Earth's rotation around its axis, the planet's orbit around the sun, the solar system's trajectory through the Milky Way, and the galaxy's motion through the universe.

Why time ticks faster on the moon, which may need its own time zone

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.

Time may be an emergent, rather than a fundamental, property of the universe

Some theories of everything—mathematical models that try to explain all aspects of the universe, including quantum phenomena and gravity—do not incorporate time. If a time-neglecting version of such a theory were ever validated, it might suggest that time is a feature that emerges from our limited perception of the universe.

Meteorological v. astronomical seasons, explained

Meteorologists and climatologists define seasons differently from “regular” or astronomical spring, summer, fall, and winter. Traditional seasons reflect the movement of celestial objects, known as the astronomical seasons; meteorologists mark seasonal change based on temperature averages.

Ancient Egyptian papyrus from 16th century BCE seems to reference tinnitus

Ancient Egyptians wrote that they treated "bewitched ear" with herbal concoctions that involved frankincense and other ingredients, which were placed in the ear.

The calendars of the 'Lord of the Rings'

JRR Tolkien's epic fantasy trilogy "The Lord of the Rings" is a seminal work in the history of literature partly due to its creator's obsessive focus on systematic detail—including the calendars used in the world. Take a fantastic dive into the minutiae of Tolkien's creation by learning the different approaches to time organization in the Shire or Rivendell with this dense, comprehensive resource based on Tolkien's appendices.

The legend of the Chinese zodiac involves a race between animals

The legend of the Chinese zodiac says that to help people keep time, the emperor of the gods established a 12-year cycle, with each year symbolized by a different animal. To choose the animals, he held a cross-river race. Each of the winning animals used their unique skills to get across the river: The snake is sneaky, the rabbit is nimble, and the rat is cunning. These characteristics are believed to be mirrored by those born under the animals’ zodiac signs.

The solar system formed between 4.5 and 4.6 billion years ago

Its age is best estimated by studying meteorites from the early formation period of the planetary system, including Erg Chech 002 (4.565 billion years old) and NWA 11119 (4.5648 billion years old). Solar analysis and stellar evolution models estimate the sun's age to be approximately 4.57 billion years.

The term 'algorithm' originated from the Latinized name of al-Khwārizmī, a 9th-century mathematician whose works introduced Arabic numerals and the decimal-based numeral system to Europe and whose treatise 'Al-Jabr' gave algebra its name.

Visualize the path of every solar eclipse from 1900 to 2099 and see what each looks like when observed from different locations on Earth.

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

Stanford built a Google Maps for the Roman Empire, revealing how much it cost to travel in the ancient world

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

Scientists can determine Earth's past climate conditions by analyzing air trapped in microscopic bubbles within ice cores—columns of compressed snow layers that build up over hundreds of thousands of years.

Track the location of the Voyager probes, currently between 13 and 15 billion miles away from Earth.

Chaos theory—informally known as the butterfly effect—is the reason why weather forecasts are presented with probabilities rather than certainties.

The first horror movie is believed to be George Méliès' 1986 short 'The Haunted Castle,' which pioneered the use of special effects

Clever Hans was a 1900s horse that was believed to be able to solve math equations, tell time, and read and comprehend German, until a psychology student discovered how he got his answers.

Shooting stars, or meteors, are fragments of asteroids and comets that burn up as they enter Earth's atmosphere, creating streaks in the sky called meteor showers.

The word 'jazz' evolved from 'jasm,' 19th-century American slang for 'energy'

Apollo astronauts left items in the moon's 'toss zone,' including golf balls, family photos, and bags of human waste, to make room for lunar rocks.

Apeirophobia is an overwhelming fear of living forever, perhaps stemming from the brain's inability to conceptualize an infinite life.

Trace how the Bill of Rights, inspired by centuries of political theory, took shape between 1774 and 1789.

The American cockroach is actually from Africa, an apparent hitchhiker aboard ships carrying enslaved people, with evidence suggesting the bug may have arrived in the New World as early as the 1600s.

While the first exchange-traded fund (a 'basket' of different assets that can be bought and sold on a stock exchange) in the US only launched in 1993, the global ETF market has grown to more than $10T in the short time since.

The Mona Lisa's celebrity status and repeated restorations have obscured what made the painting so revolutionary for its time

Long before Major League Baseball began allowing instant replay for balls and strikes, an umpire reluctantly used the technology to determine whether a hit was a home run, a move that inadvertently ushered in a new era for the sport.

Budweiser stores yeast derived from the original 1800s strain in a secret bunker, which only the Head of Yeast Management can access—not even the CEO

Take a 3D tour of the Hajj, Islam's annual pilgrimage to Mecca, undertaken by over 1.5 million Muslims.

Objects can be 3D printed with light by projecting 2D computerized tomography (CT) scans onto rotating cylinders of resin, which solidify upon exposure.

One disco producer saw 'Star Wars' four times on its opening weekend and was so inspired that he recorded the album 'Star Wars and Other Intergalactic Funk,' which produced a chart-topping single.

Coral polyps reproduce via broadcast spawning, where entire reefs simultaneously release reproductive cells for about one hour, once a year.