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How Ancient Greeks Set Humanity on the Path to Space Exploration

Ancient Greek astronomers space
A clash among members of a famous galaxy quintet in space reveals an assortment of stars across a wide color range from young, blue stars to aging, red stars. Ancient Greek astronomers paved the way for our modern understanding of the heavens. Credit: NASA and ESA Public Domain

Ancient Greek astronomers were some of the first people to gather knowledge about space exploration.

Business moguls Sir Richard Branson and Jeff Bezos should be thanking ancient Greek astronomers for being able to realize their travel off the face of the earth and into space.

As civilized societies were just learning to use the wheel on earth, the ancient Greeks were aiming at the sky and the stars, contemplating outer space and how to measure it.

Even the science of the study of the sky and the stars, astronomy, finds its root in the ancient Greek word “Astronomia.”

Ancient Greeks led the way in the understanding of space

It was under Greek skies that ancient astronomers began to develop theories about the planets overhead, theories that are now proven. Christopher Columbus may or may not have set out to prove that the earth was spherical, but it was the ancient Greek astronomer Aristarchus who initiated the theory that the universe is heliocentric and that the planets are round.

The Babylonians of Mesopotamia first looked to the skies and postulated that the stars, the moon, and the sun were gods that ruled over men. However, it was the ancient Greeks who analyzed those theories of deities and turned them into mathematical equations and calculations.

If you really want to travel to the stars, there is an easier way than heading to Cape Canaveral, where NASA launches rockets from Florida into outer space, or getting an extraordinarily pricey ticket aboard the craft that Branson and Bezos will travel on this month.

If you can get to the Acropolis, just a few hundred meters away is the National Observatory, known in Greece as the Asteroskopeio. From the observatory, positioned directly across from the Acropolis on Lofos Nymphon in central Athens, you can get a bird’s eye view of Mars and the moon through the “Doridis” refractor telescope.

National Observatory Athens
The National Observatory with a telescope that allows the public to view the stars directly across from the Acropolis. Credit:  Dimboukas Creative Commons Attribution 4.0 International

The National Observatory of Athens was founded in 1842 as the first research center of modern Greece. Its history is linked with the evolution of basic and applied research, the development of services provided to the Greek State and society at large, and the promotion of science.

And how amazing that literally just steps away from where ancient Greek astronomers conducted their first experiments, contemporary Greek astronomers are working and can show you the planets in the night sky.

Metonas the Mathemetician and Ancient Greek Astronomer

Metonas was a Greek mathematician, astronomer, and engineer who lived in Athens in the 5th century BC. He is best known for his 432 BC calculations on the Metonic cycle for the lunar calendar year of Attica.

Metonas’ calendar assumes that nineteen solar years are equal to 235 lunar months, which amounts to 6,940 days. This system arose from calculations made by Metonas based on his own astronomical observations and confirmed by Aristarchus 152 years later.

According to the testimonies of ancient historians, Metonas installed the first Heliotropion, or Helioscope, in Pynx in Athens. The foundations of the Helioscope are still visible just behind the steps leading to Pnyx, the archaeological site perched on a small, rocky hill, just over 330 feet high in the center of Athens.

The site is located in a large park just below the National Observatory to the west of the Acropolis. Metonas determined the dates of the equinoxes and the solstices based on the specific location of this helioscope.

From this position, the sunrise during the summer solstice can be viewed from the top of Mt. Lycabettus while, six months later during the winter solstice, the sun rises from the top of Mount Hymettus. The annual apparent movement of the sun on the horizon creates an arc of sixty degrees, the bisector of which is aligned with the rock of the Acropolis. The exact determination of the summer solstice was important to the ancient Athenians because the first moon after the summer solstice marked the beginning of the new year.

Who Were the Other Ancient Greek Astronomers?

Metonas was one of many ancient Greek astronomers to formulate calculations while gazing at the skies above. Renowned mathematicians, many of these scholars, branched off in astronomy, cataloging, calculating, and observing. Whether they cataloged stars, contemplated shapes, or tried to measure the physical space within and beyond the borders of earth, their work put contemporary man in the sky.

Today, it is hard to believe in any other notion than spherical planets that revolve around the sun.

Pythagorean Theorem and a Spherical Earth

Pythagoras of Samos, who lived from 570 to 495 BC, was an ancient Greek astronomer and philosopher and the eponymous founder of Pythagoreanism. Pythagoras was credited with many mathematical and scientific discoveries in antiquity. Since at least the first century BC, Pythagoras has commonly been given credit for discovering the Pythagorean theorem in geometry, which states that “in a right-angled triangle the square of the hypotenuse is equal (to the sum of) the squares of the two other sides.”

It was said that he was the first man to call himself a philosopher, a “lover of wisdom,” in the Greek language, (philo/friend of sophia/wisdom).  He was the first to divide the globe into five climatic zones.

In astronomy, Pythagoras is credited with the belief that the earth is spherical and for identifying the morning and evening “stars” that we know today as the planet Venus. By the end of the fifth century BC, this fact was universally accepted among Greek intellectuals.

Ancient Greek Astronomer Philolaus

Philolaus, who lived from 470 to 385 BC, was a Greek Pythagorean and pre-Socratic philosopher. He was born in a Greek colony in Italy and migrated to Greece. Philolaus has been called one of three most prominent figures in the Pythagorean tradition and the most outstanding figure in the Pythagorean school.

Pythagoras developed a school of philosophy that was dominated by both mathematics and mysticism. Most of what is known today about the Pythagorean astronomical system is derived from Philolaus’ views. He may have been the first to write about Pythagorean doctrine.

Philolaus asserted that the earth was not the center of the universe, rebelling against the geo-centrism of the time. He is credited with the earliest known discussion of concepts in the development of heliocentrism, insisting the sun is the center of the human universe.

The Archimedes Principle—One of the First Astronomers

Archimedes of Syracuse, who lived from 287 to 212 BC, was an ancient Greek astronomer, mathematician, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists of classical antiquity. The most widely known anecdote about Archimedes tells of how he invented a method for determining the volume of an object with an irregular shape.

Archimedes’ principle involved a metal bar, placed into a container of water on a scale. It displaces as much water as its own volume, increasing the mass of the container’s contents and weighing down the scale.

A votive crown for a temple had been made for the king of Syracuse, who had supplied the pure gold to be used. Archimedes was asked to determine whether some silver had been substituted by a dishonest goldsmith. Archimedes had to solve the problem without damaging the crown, so he could not melt it down into a regularly-shaped body to calculate its density.

Archimedes noticed while taking a bath that the level of the water in the tub rose as he got in. He realized that this effect could be used to determine the volume of the crown. For practical purposes, water is incompressible so the submerged crown would displace an amount of water equal to its own volume.

By dividing the mass of the crown by the volume of water displaced, the density of the crown could be obtained. This density would be lower than that of gold if cheaper and less dense metals had been added. Archimedes then took to the streets naked, so excited by his discovery that he had forgotten to dress himself, crying “Eureka,” which in Greek sounds like evreeka, literally meaning, “I have found it!”

The test on the crown was conducted successfully, proving that silver had indeed been mixed in with the gold.

Archimedes also explored astronomical measurements of the earth, the sun and the moon, as well as Aristarchus’ heliocentric model of the universe. Despite a lack of trigonometry and a table of chords, Archimedes described the procedure and instrument used to make observations, a straight rod with pegs or grooves, applied correction factors to these measurements, and finally gave the result in the form of upper and lower bounds to account for observational error.

Ptolemy, quoting Hipparchus, also references Archimedes’ solstice observations in the “Almagest.” This would make Archimedes the first known ancient Greek astronomer to have recorded multiple solstice dates and times in successive years.

Ptolemy’s Astrolabe and Astronomy in Ancient Greece

Ptolemy, 335 to  405 BC, used an astrolabe to record astronomical observations.

Today, we know the exact time, positions of the stars and planets, and our exact location, to the tenth of a degree, but this knowledge was available to the ancient Greeks as well, thanks to the invention of one device, the astrolabe.

The scientist Ptolemy, who lived in Alexandria, was the brilliant mind behind this genius machine, which used sets of dials to determine altitude and  latitude—as long as the time was known—the shifting positions of stars and planets, and to survey or triangulate your location on land.

Basically, the astrolabe was a handheld model of the universe. Its many functions also made it an elaborate inclinometer and an analog calculation device that was capable of working out several kinds of problems in astronomy.

The importance of the invention of the astrolabe comes not only from the early discoveries in astronomy but also from the ability to determine latitude on land or on calm water, making it possible to navigate the seas in a limited way.

Ancient Greek Astronomer Aristarchus’ Heliocentric Model of the Universe

Aristarchus of Samos, who lived from 310 to around  230 BC, was an ancient Greek astronomer and mathematician who presented the first known heliocentric model that placed the sun at the center of the known universe with the earth revolving around the sun once a year and rotating about its axis once a day. Aristarchus identified the “central fire” with the sun. He put the other planets in their correct order of distance around the sun.

Aristarchus suspected that the stars were just other bodies like the sun, albeit farther away from earth. His astronomical ideas were rejected in favor of the geocentric theories of Aristotle and Ptolemy.

Aristarchus estimated the sizes of the sun and moon as compared to earth’s size. He also estimated the distances from the earth to the sun and moon. He is considered one of the greatest astronomers of antiquity.

Ancient Greek Astronomer Aristarchus
Aristarchus of Samos developed the first mathematical formula of astronomy to calculate planet size. Credit: Screenshot Youtube

Since Aristarchus suspected the stars were other extremely distant suns, there was no observable parallax—that is, a movement of the stars relative to each other as the earth moves around the sun. Since stellar parallax is only detectable with telescopes, his accurate speculation was unprovable at the time.

It was not until the sixteenth century that a mathematical model of a heliocentric system was presented by the Renaissance mathematician, astronomer, and Catholic cleric, Nicolaus Copernicus, leading to the Copernican Revolution. In the following century, Johannes Kepler introduced elliptical orbits, and Galileo de’ Galilei presented supporting observations made using a telescope.

Ancient Greek Astronomer Eratosthenes Calculated the Earth’s Circumference

Eratosthenes of Cyrene, who lived from 276 BC to 195 BC, was an ancient Greek astronomer who was also a multi-discipline scholar, or polymath. He was a mathematician, geographer, poet, astronomer, and music theorist. He was a man of such learning that he also became the chief librarian at the Library of Alexandria. His work is comparable to what is now known as the study of geography, and he introduced some of the terminology still in use in the discipline today.

Eratosthenes is best known for being the first person known to calculate the circumference of the earth, which he did by utilizing the extensive survey results he had access to in his role at the Library of Alexandria. His calculation was remarkably accurate. He was also the first to calculate earth’s axial tilt, which also proved to be remarkably accurate. He created the first global projection of the world, incorporating parallels and meridians based on the available geographic knowledge of his era.

Eratosthenes was the founder of scientific chronology. He endeavored to revise the dates of the main events of the semi-mythological Trojan War, dating the Sack of Troy to 1183 BC. In number theory, he introduced the sieve of Eratosthenes, an efficient method of identifying prime numbers.

The measurement of Earth’s circumference is the most famous among the results obtained by Eratosthenes, who estimated that the meridian has a length of 252,000 stadia with an error on the real value of less than two percent. Eratosthenes described his arc measurement technique in a book entitled On the measure of the Earth.

Ancient Greek Astronomer Hipparchus Compiled Star Catalogue

Hipparchus of Nicaea, who lived from 190 to 120 BC, was yet another ancient Greek astronomer. He erected an early observatory on the island of Rhodes around 150 BC and set about compiling a star catalogue with approximately 850 entries. Hipparchus calculated the celestial coordinates for each star using the first known trigonometric table and developed and improved several astronomical instruments, including the astrolabe.

Dedicated to Hipparchus’ contribution to the early study of the solar system, a crater on the surface of Mars was named after him in 1973. A larger crater on the moon was also named after the ancient Greek astronomer.

Antikythera Mechanism Calculates Planetary Movement

The Antikythera Mechanism, often referred to as the world’s first computer, was discovered inside an ancient shipwreck by Greek sponge divers on May 17, 1901. After numerous studies, it was estimated to have been constructed between 150 BC and 100 BC. A later study places it at 205 BC, just seven years after the death of Archimedes.

The world’s oldest surviving mechanical calculator, it was used by ancient Greek astronomers. The device has eroded somewhat due to the passage of time, but when it was intact, it would have appeared as a box, housing dozens of finely machined bronze gear wheels.

When manually rotated by a handle, the gears spun dials on the exterior showing the phases of the moon, the timing of lunar and solar eclipses, and the positions of the five planets (Mercury, Venus, Mars, Jupiter, and Saturn) known at the time at different times of the year. This even accounted for their retrograde motion—an illusionary change in the movement of planets through the sky.


Antikythera astronomy space calculator
The moving parts of a reproduction of the Antikythera Mechanism, an ancient analog computer. Credit: Freeth, T., Higgon, D., Dacanalis  Creative Commons Attribution 4.0 International

It may even have been the work of Archimedes himself, but there is no documentation of that; there is only speculation. Gearing technology with the sophistication of the Antikythera Mechanism was not seen again for a thousand years.

The ancient calculator also includes an astrological calendar, as the indicators seem to revolve around the zodiac, revealing the movements of both the moon and the planets.

Antikythera Mechanism - ancient Greek Astronomers
A reproduction of the Antikythera Mechanism on display at the National Observatory in Athens. Credit: Moravec Creative Commons Attribution-Share Alike 4.0 International

The National Observatory is the contemporary location for a journey to the stars. As noted above, the Asteroskopeio is within close proximity to the physical space used by ancient Greek astronomers who contributed so much of what we know of the universe today.

Ancient Greek astronomers, such as Metonas, Pythagoras, Philolaus, Eratosthenes, Ptolemy, Aristarchus, Hipparchus, and Archimedes, developed the theories of calculation of the size, the time, and the distance of planets within the solar system. These contributions were the building blocks that have made journeys into space possible today.

Progress was marked by enlightened and renowned scientists in Greece who paved the way to knowledge with the creation of the Asteroskopeio in the 1800s. Thanks to the National Observatory, visitors to Athens can travel, so to speak, to the stars, even if they are not Richard Branson or Jeff Bezos.

The tycoon Branson said, “After more than 16 years of research, engineering, and testing, Virgin Galactic stands at the vanguard of a new commercial space industry, which is set to open space to humankind and change the world for good.”

Let’s hope he remembers to thank all those ancient Greek astronomers and not just the people who work for Virgin Galactic.


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