An astronomical transformation

Our interpretation of the universe and our place in it has slowly evolved over time. From hollow wheels of mist to fiery gas bodies, we’ve come a long way in 2,600 years.

Illustration by Kayla Oliver

Illustration by Kayla Oliver

When I was eight, I watched the movie The War of the Worlds at school. I’d like to think my teacher was trying to introduce our young minds to the impact art could have on society. Whether it was intentional or not, he did succeed in instilling me with a sense of wonder for the planet Mars, the stars and the possibilities beyond them. Even though the images on screen were enthralling, I now know The War of the Worlds is just a movie, and that astronomy is the key to a true understanding of the universe. Our understanding of what lies beyond our planet has evolved drastically over the last few hundred years, morphing from civilisations that worshipped the stars, to astronomers tracking their movements across the sky in modern observatories. But all of this is driven by the same sense of wonder I felt watching The War of the Worlds — the desire to try and make sense of the world and our place in the universe. 

We can trace the first scientific forays into studying the universe back to the Ionians. Around the beginning of the sixth century, an intellectual revolution began on the Greek Ionian coast. This was essentially the birth of the scientific method, and the Greeks were exploring the notion that natural phenomena could be understood rationally through observation — rather than attributing every event to some kind of deity. What we now call myths were once a way for ancient civilisations to explain how things came to be. Zeus was responsible for lightning, Apollo for light, and Poseidon for the sea. Human pursuits were also divinely governed or at least influenced by figures like Ares, god of war, and Aphrodite the god of love. 

A hybrid of philosophical thought and practical experience allowed Ionians to use rationality to let go of their Olympians and Titans, at least when it came to explaining natural events. The Ionian scientific enlightenment helped transform the worship of Greek Gods into the storytelling of Greek mythology. 

Anaximander was the first of the Greeks to propose a model for the movement of the planets. While he incorrectly described Earth as the centre the planets were circling, his model did introduce a sense of depth with each planet orbiting at a different distance from the Earth. Anaximander also described the Earth as cylindrical in shape, about one-third as high as its diameter, with an atmosphere comprised of layers of air, fire and then vapour. Humans lived on the flat top of the cylinder, surrounded by ocean. He believed that the opposite flat surface was habitable land, although he wasn’t sure if it was inhabited by people.

 
One of the earliest models of the Earth was Anaximander’s cylinder. Anaximander studied the movement planets and was one of the first to believe they orbited Earth. Popular Science Monthly Volume 10/Wikimedia Commons (CC BY 1.0)

One of the earliest models of the Earth was Anaximander’s cylinder. Anaximander studied the movement planets and was one of the first to believe they orbited Earth. Popular Science Monthly Volume 10/Wikimedia Commons (CC BY 1.0)

 

Anaximander’s model described the celestial bodies as hollow wheels of mist, filled with fire. The wheels had small openings through which the fire was visible, and this was what we saw as the sun, moon and stars. Sometimes these openings would close, and this explained eclipses and the phases of the moon. Anaximander reasoned that the wheel shape of the celestial bodies kept them in their circular orbits around Earth, never falling to the ground.

Today we know that the Earth is spherical, not cylindrical and all the land on Earth is inhabited to some degree. There is no fiery layer to our atmosphere and we’re not at the centre of the solar system. Compared to what we now know from astronomy, Anaximander’s model seems as inaccurate as the mythology that preceded him, but his was the first attempt to explain the nature of the universe through observation and reason. He introduced concepts of infinity (to describe the expanse of the universe) and equilibrium (to explain the ‘balance’ that kept Earth afloat in space). While not entirely accurate, his ideas marked the beginning of our desire to understand the universe through science rather than mythology.

From Ancient Greece to Renaissance Italy

While the church has in many ways been a great patron of the sciences — funding many of the world’s hospitals and medical facilities — its dogmatic nature is inherently opposed to the scientific method that relies on constant testing, debate and scrutiny. Dating back to the third century BC, geocentrism was the untested popular belief for almost two millennia, and this suited the church just fine. Up until the 17th century, the prevailing view had been that the Sun, planets and all objects in space orbited a stationary Earth. This fit well with the Catholic belief of man’s position of privilege having been created by God.

Geocentrism was developed from ideas put forward by early astronomers. While Apollonius of Perga proposed the idea in the third century BC, it was Ptolemy of Thebaid who formalised the theory in the second century AD. In addition to placing the Earth at the centre of the universe, it also stated that the planets’ orbits were perfect circles. In order to explain the observed changes in brightness of the planets or appearance of moving in a different direction, the idea of the epicycle was introduced. Epicycles explained these observations of the planets at the expense of increasing the complexity of the geocentric model.

 
Epicyclic orbits around Earth allowed for the brightness of planets to change and kept the orbit (deferent) circular. Dhenry/Wikimedia Commons (CC BY 1.0)

Epicyclic orbits around Earth allowed for the brightness of planets to change and kept the orbit (deferent) circular. Dhenry/Wikimedia Commons (CC BY 1.0)

 

To get the idea, imagine a planet orbiting Earth around an imaginary circle, called the deferent. The planet travels around on its orbit while also moving along yet another imaginary circle, the epicycle. The planet’s movement along the epicycle and it’s deferent combined to produce an orbit, which if it had to be drawn on paper, would resemble a complex pattern similar to a spirograph.

This model preserved the circular perfection of the planets’ orbits around the Earth but required complicated mathematics and explanations to support the view. For example, the centre of any of the planets’ deferent was not the Earth, but rather a short distance away and it differed for each planet. The Sun didn’t have an epicycle, but the Moon did. While the epicycle of each planet moved in the same direction as their deferents, the opposite was true for the Moon. Ultimately, Ptolemy’s geocentric view of the universe (Solar System) included 40 cycles and epicycles. Other than being questioned by Muslim scholars in the 10th century, it was accepted for another 1300 years in Western civilisation.

Are we the centre of it all?

In the early 1500s, Nicolaus Copernicus found Ptolemy’s geocentrism inelegant and cumbersome. By proposing the drastic change that the Sun was at the centre of the known universe and that Earth’s rotation was the reason for the movement of the stars, Copernicus actually created a much simpler model. This meant that all the known planets at the time (Mercury, Venus, Mars, Jupiter and Saturn) orbited the Sun, while the Moon orbited the Earth. Copernicus kept the circular orbits intact with his heliocentric model, which meant each planet moved at the same speed throughout their orbits. In the early 1600s, Johannes Kepler recalculated the movements of the planets as ellipses, using precise data collected by Danish astronomer, Tycho Brahe. Kepler’s descriptions and calculations of the planetary motions are now known as Kepler’s Laws.

Galileo Galilei was able to confirm Copernicus’ and Kepler’s work when he used his telescope to observe Jupiter and Venus. By observing Jupiter’s four largest moons: Ganymede, Callisto, Io and Europa, Galileo was able to demonstrate that not everything in the sky was orbiting Earth. By observing Venus, Galileo saw that it went through phases like the Moon and that it was larger at certain times of the year, which made no sense if it were to adhere to the circular orbits of geocentrism.

In 1616, Galileo was summoned to Rome and ordered not to teach or write about his findings, and his support of the heliocentric model. Disobeying his clerical orders in 1632 he was branded a heretic and placed under house arrest for the last nine years of his life, for publishing “Dialogue Concerning the Two Chief World Systems”, which was structured as a conversation between a geocentrist, Simplicio, and heliocentrist, Salviati. While Galileo was granted permission to publish the book by Pope Urban VIII on the basis that it didn’t promote either world view over the other, Salviati was positively portrayed by Galileo in the dialogue, while Simplicio’s view was ridiculed. 

The church had long been the chief provider of guidance in how to interpret the universe. Any viewpoints and theories that contradicted scripture were labelled as heresy, causing heliocentric works to be banned until 1758. But by removing ourselves from a perceived position of privilege, we took a closer step to understanding our place in the universe, a position that was eventually accepted by the Church.

What do the stars mean to you?

Galileo, Copernicus, and Kepler heralded the dawn of the scientific study of celestial bodies: astronomy. But astronomy is not the only method humans have produced to interpret the heavens. Many people use astrology (the interpretation of the effect that celestial bodies have on human existence) as a way to understand our place in the world.

While not rooted in scientific consensus, astrology has a long history, starting in 3000BC when Mesopotamian sky watchers first joined the sparkling dots in the sky to make constellations. The Babylonians introduced the zodiac around 1800BC, which is a depiction of how the sequence of planets, constellations, and the Sun appear to move in relation to the observer’s perspective on the ground.

The bright band of the Milky Way over The Pinnacles desert in Western Australia. Throughout history, the motion of the stars has mystified and intrigued us sparking astronomers and astrologers to search for meaning. inefekt69/Flickr (CC BY-NC-ND 2.0)

The bright band of the Milky Way over The Pinnacles desert in Western Australia. Throughout history, the motion of the stars has mystified and intrigued us sparking astronomers and astrologers to search for meaning. inefekt69/Flickr (CC BY-NC-ND 2.0)

Astrologers interpreted the motions of the planets relative to the constellations for guidance or omens to predict the outcome of battles, affairs of the state and the fortunes of ordinary people. Babylonian priests made their predictions by considering past events or outcomes that had occurred while a particular constellation was visible. For example, if victory had been attained over an enemy under a half moon, it would then be considered a favourable omen. While astrology was fairly accurate at predicting the patterns of movements of celestial bodies, the effect these movements have on human events is generally accepted as fanciful.

What do we think now?

For the last few centuries, our understanding and knowledge of the universe has been expanding at a rapid rate. Over 3000 planets have been identified by astronomers in the last 20 years alone. On 2 August 2016, it was announced that an Earth-like planet had been found orbiting Proxima Centauri, the closest star to our Solar System. The planet has been named Proxima B, and it is 4.85 billion years old. This means Proxima B is older than our Sun which is a mere 4.6 billion years old. It sits a little over 4 light years away from Earth, which in astronomical terms is right under our nose. While the discovery of exoplanets like Proxima B is driven by the same sense of curiosity the ancient Babylonians and Greeks had, sophisticated instruments have been used to discover these worlds. 

For more than 15 years, astronomers at the European Southern Observatory in Chile have used the Ultraviolet and Visual Echelle Spectrograph (UVES) and the High Accuracy Radial velocity Planet Searcher (HARPS) to hunt for such planets. These instruments detect wobbles in a star’s movement caused by gravitational tugs of the orbiting planets that they’re searching for. Data collated from UVES and HARPS from the last 16 years allowed astronomers to confirm the finding. While we no longer look towards planets like these to tell our fortune, Proxima B represents a possible future for our civilisation. Its discovery has excited astronomers for its striking similarities to Earth, most notably the fact that it circles Proxima Centauri’s habitable zone: the range of distances ideal for liquid water to form. Coupled with its rocky composition, the potential presence of water means that Proxima B may be able to host life or support it.

The possibility of life on another planet brings me back to the sense of wonder I felt from watching The War of the Worlds as a kid. Could it be possible that within the same lifetime, an eight year old can imagine another planet capable of sustaining life, then as a grown man witness its discovery? As Carl Sagan said: “We began as wanderers, and we are wanderers still. We have lingered long enough on the shores of the cosmic ocean. We are ready at last to set sail for the stars.” Whether it was through creation stories, telescopes or sophisticated instruments like UVES and HARPS, over several millennia our understanding of the universe has evolved over time like ourselves, and will likely continue to do so.

Edited by Tessa Evans and Bryonie Scott