The sun is the flaming crown of Helios as he rides across the sky from east to west on his flying chariot, or so the ancient Greeks thought. Our understanding of the sun, moon and stars has advanced dramatically since then, but not without centuries of conflict and dispute.
Ancient civilisations believed the stars and planets to be the work of gods, giving birth to numerous belief systems based around celestial formations and movement. Astrology as we know it today has persisted in some form or another since the earliest Babylonian societies first documented it some five thousand years ago.
The Greek civilisation was the first to truly advance our understanding of the cosmos. By observing ships disappearing over horizons they reasoned that the Earth must be spherical and placed it at the centre of the universe, founding the geocentric model. Aristotle developed the theory of celestial orbs, in which the Earth lies at the centre of a series of concentric spheres, upon which all stars and planets are luminous spots. The astronomer Ptolemy then created a complex mathematical model to iron out its inconsistencies. Although Aristarchus of Samos and Heraclides Ponticus realised that the sun was the centre around which Earth orbited as early as 300 BC, their theories were disregarded in favour of Aristotle’s until the 15th century AD.
In the late 15th century, Polish polymath Copernicus returned to Ptolemy’s model in an attempt to solve its various inaccuracies. After studying masses of astronomical data he concluded that the Earth and all other planets orbited the sun, a view that matched perfectly with observation. However, this new ‘heliocentric’ theory was deplored by the church and with some believers of heliocentrism being executed, Copernicus kept his work secret, publishing it only on his deathbed.
A whole century after Copernicus, the German astronomer Kepler published his now famous three laws of planetary motion, showing that planetary orbits are ellipses rather than circles and that planets sweep out equal areas in their orbits in equal times. For the first time, Kepler offered a way to explain astronomy as the result of physical laws.
Following work by Galileo, it took the consistency of Newton’s laws of motion and theory of gravitation for both Earth-based and celestial objects to prove Copernicus and Kepler right, and thus a new era for heliocentrism was born. Newton’s laws relating a planet’s mass to the gravitational force it exerts were to remain unchallenged for a further 200 years until another figure would add the final twist in our understanding of space: Einstein.
Einstein, building on the newly discovered idea that the speed of light is constant, was able to infer several surprising truths about our universe. He declared that time doesn’t run at a steady rate and in fact slows down with increasing velocity. Astoundingly, he found that gravity actually warps space itself, changing the ancient intuitive assumption that travelling in a straight line will lead you so. Understanding of the cosmos has snowballed since the turn of the 20th century. The big bang is already a cornerstone of most schoolbooks despite being less than a century old. With space exploration thriving, we stand today knowing more about our galactic surroundings than at any time in the past. Yet with so much remaining unknown, we can gaze up at the night sky with as much mystery as ever before.