According to the Greek historian Herodotus, the first person to successfully predict a solar eclipse was the Greek philosopher Thales of Miletus in 585 BCE, with the resulting celestial event ending a half-decade-long war.

By identifying patterns in the periodic movements of the sun, moon, and Earth, ancient civilizations realized that identical eclipses repeat about once every 6,585 days, known as the saros cycle.

In the third century BCE, the Greek astronomer Aristarchus of Samos estimated the distance to the moon using geometry after measuring the length of Earth's shadow during a lunar eclipse.

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.

Four astronomical discoveries from ancient Greece

Modern astronomy relies on making discoveries without being present on the planets, stars, galaxies, and other objects studied. Imagine the difficulty the ancient Greeks had studying them without computers and telescopes. Yet somehow they calculated precise measurements of planetary distances, sizes, and more. Read this page to learn more about early triumphs in astronomical science.

How the ancients calculated Earth's size correctly

Watch this seven-minute video to hear Carl Sagan explain how ancient Greek polymath Eratosthenes correctly calculated the size of the Earth in the third century BCE. At some point, Eratosthenes noticed a discrepancy in the length of shadows cast in different cities during the summer solstice. This observation grew into a simple experiment that enabled Eratosthenes, the head librarian at the Library of Alexandria, to calculate the Earth's size precisely.

Ancient Greek astronomer Hipparchus created accurate maps of the night sky way ahead of his time, with coordinates sometimes within a single degree of modern values.

Ancient Greek told to kick rocks after claiming moon wasn't a deity

About 2,500 years ago, ancient Greek philosopher Anaxagoras theorized that the moon probably wasn't a goddess. This article explains how this belief led to his exile. Anaxagoras also argued the sun was just a burning rock, writing that it was the sun that illuminated the moon. According to this resource, this theory enabled Anaxagoras to accurately explain eclipses and lunar cycles.

In 1676, Danish astronomer Ole Rømer determined that light did not travel instantaneously by observing a delay in the appearance of eclipses on Jupiter when it was farther from Earth.

While solar eclipses were considered ominous throughout history, multiple cultures explained the celestial event as the result of mythical creatures nearly consuming the sun.

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

The prophetic Oracle of Delphi was believed to have a direct line to the Greek god Apollo.

Aristotle discovered that Earth was spherical by observing the round shadow it cast on the moon during lunar eclipses and by noting that different constellations were visible from different latitudes.

Scientists validated Albert Einstein's theory of gravity by measuring the apparent positions of stars via their starlight as it traveled near the sun on its way to Earth during a total solar eclipse.

Over thousands of years, the frequency of solar eclipses is greatest around the Arctic and Antarctic Circles and lowest near the equator.

The ancient Greeks and Romans viewed comets and meteors as divine omens

Both considered the appearance of a comet or its fragments as a precursor to significant events, such as the birth of a notable figure or the death of a ruler. One observed in 44 BCE was believed to be a sign of the deification of Julius Caesar after his assassination.

Humans have speculated about alien life since ancient times

Around 50 B.C.E., Roman poet and philosopher Lucretius shared the idea that alien life was possible, which was put forth by Greek philosopher Epicurus. The writing is believed to be the first straightforward assertion in Western literature that aliens must exist.

East Asian records of auroras may date back to 10,000 BCE

Ancient texts from Japan, Babylon, and China contain accounts of auroras dating back millennia. Because auroral activity and intensity are driven by periodic ebbs and flows in solar activity, these records allow scientists to identify patterns that may help anticipate particularly dangerous future solar storms.

Ancient Greece originated roughly 4,000 years ago around the Aegean Sea, and over centuries expanded as far as Spain and India.

The scientific name for northern lights came from two Greco-Roman gods

Although cave paintings may have depicted them millennia earlier, one of the oldest known references to auroras is a Babylonian cuneiform tablet from about 600 BCE. In 1619, Galileo Galilei named the phenomenon in the northern hemisphere "aurora borealis" after the Roman goddess of dawn—Aurora—and the Greek god of the north wind—Boreas.

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.

The marathon’s roots can be traced back to a Greek myth

Legend has it that the first marathon took place in 490 BCE, when Pheidippides, an ancient Greek soldier, ran from the Battle of Marathon back to Athens—approximately 25 miles—to inform his people they’d defeated the Persians. The story is likely apocryphal: No Greek historian mentioned it until over 500 years later.

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

A timeline of the ancient Greeks

When exactly were the Ancient Greeks around on Earth? Their roots go back nearly 9,000 years to the Bronze Age with the so-called Minoan civilization. These sea-faring tribes would come together to hold off the invading Persian Empire and culminate in the glories of Athenian democracy, Spartan military discipline, and more. Check out this thorough timeline of the Ancient Greeks.

View depictions of world maps throughout history

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.

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.

Solar eclipses are a cosmic coincidence because the moon is 400 times smaller than the sun but 400 times closer to Earth, allowing it to completely block sunlight.

The 16th-century astrologer Nostradamus' predictions for 2024

Nostradamus has been credited with predicting several major historical events over the years, but what does he think is in store for 2024? Read up on what his mysterious 1555 book, The Propheties, hints at for the upcoming year.

View historical records of solar observations and discoveries, from telescopes in the early 1600s revealing sunspots to NASA's Parker Solar Probe photographing the sun from within its outer corona in 2025.

The ancient Greeks and Romans were known to take vacations.

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.

The ancient Games at Olympia ended after 1,500 years due to economic issues

The ancient Olympics came to an end in 393 CE, and some historians point to Christian Roman emperor Theodosius I's ban on celebrating pagan festivals. This article explores an alternative theory: a bad economy. The writers cite the Theodosian Code, which makes no mention of the Olympics, and multiple records that mention the Olympics after Theodosius' death.

Watch the many different civilizations around the Mediterranean shift power from the year 2500 BCE to 0 BCE in this animated map.