Trace the Earliest History of Astronomy

Claudius Ptolemy
Claudius Ptolemy with an armillary sphere he used to predict solstice dates and other celestial sights. Public domain, via Wikimedia Commons.

Astronomy is humanity's oldest science. People have been looking up, trying to explain what they see in the sky probably since the first "human-like" cave dwellers existed. There's a famous scene in the movie 2001: A Space Odyssey, where a hominid named Moonwatcher surveys the sky, taking in the sights and pondering what he sees. It's likely that such beings really did exist, trying to make some sense of the cosmos as they saw it.

Prehistoric Astronomy

Fast forward about 10,000 years to the time of the first civilizations, and the earliest astronomers who already figured out how to use the sky. In some cultures, they were priests, priestesses, and other "elites" who studied the movement of celestial bodies to determine rituals, celebrations, and planting cycles. With their ability to observe and even forecast celestial events, these people held great power among their societies. This is because the sky remained a mystery to most people, and in many cases, cultures put their deities in the sky. Anyone who could figure out the mysteries of the sky (and the sacred) had to be pretty important. 

However, their observations were not exactly scientific. They were more practical, although somewhat used for ritual purposes. In some civilizations, people assumed that that celestial objects and their motions could "foretell" their own futures. That belief led to the now-discounted practice of astrology, which is more of an entertainment than anything scientific. 

The Greeks Lead the Way

The ancient Greeks were among the first to start developing theories about what they saw in the sky. There's much evidence that early Asian societies also relied on the heavens as a sort of calendar. Certainly, navigators and travelers used the positions of the Sun, Moon, and stars to find their way around the planet. 

Observations of the Moon suggested that Earth, too, was round. People also believed that Earth was the center of all creation. When coupled with the philosopher Plato’s assertion that the sphere was the perfect geometrical shape, the Earth-centered view of the universe seemed like a natural fit. 

Many other early observers believed the heavens were really a giant crystalline bowl arching over Earth. That view gave way to another idea, expounded by astronomer Eudoxus and philosopher Aristotle in the 4th century BCE. They said the Sun, Moon, and planets hung on a set of nesting, concentric spheres surrounding Earth. Nobody could see them, but something was holding up the celestial objects, and invisible nesting balls were as good an explanation as anything else.

Although helpful to ancient people trying to make sense of an unknown universe, this model did not help in properly tracking the motions planets, the Moon, or stars as seen from Earth's surface. Still, with few refinements, it remained the predominant scientific view of the universe for another six hundred years.

The Ptolemaic Revolution in Astronomy

In the Second Century BCE, Claudius Ptolemaeus (Ptolemy), a Roman astronomer working in Egypt, added a curious invention of his own to the geocentric model of nesting crystalline balls.  He said that the planets moved in perfect circles made of "something", attached to those perfect spheres. All that stuff  rotated around Earth. He called these little circles "epicycles" and they were an important (if erroneous) assumption. While it was wrong, his theory could, at least, predict the paths of the planets fairly well. Ptolemy's view remained the "preferred explanation for another fourteen centuries!

The Copernican Revolution

That all changed in the 16th century, when Nicolaus Copernicus, a Polish astronomer tiring of the cumbersome and imprecise nature of the Ptolemaic model, began working on a theory of his own. He thought there had to be a better way to explain the perceived motions of planets and the Moon in the sky. He theorized that the Sun was at the center of the universe and Earth and other planets revolved around it. Seems simple enough, and very logical. However, this idea conflicted with the Holy Roman church's idea (which was largely based on the "perfection" of Ptolemy's theory). In fact, his idea caused him some trouble. That's because, in the Church's view, humanity and its planet were always and only to be considered the center of all things. The Copernican idea demoted Earth to something the Church didn't want to think about. Since it was the Church and had assumed power over all knowledge, it threw its weight around to get his idea discredited. 

But, Copernicus persisted. His model of the universe, while still incorrect, did three main things. It explained the prograde and retrograde motions of the planets. It took Earth out of its spot as the center of the universe. And, it expanded the size of the universe. In a geocentric model, the size of the universe is limited so that it can revolve once every 24 hours, or else the stars would get slung off due to centrifugal force. So, maybe the Church did fear more than a demotion of our place in the universe since a deeper understanding of the universe was changing with Copernicus's ideas. 

While it was a major step in the right direction, Copernicus’ theories were still quite cumbersome and imprecise. Yet, he paved the way for further scientific understanding. His book, On the Revolutions of the Heavenly Bodies, which was published as he lay on his deathbed, was a key element in the beginning of the Renaissance and the Age of Enlightenment. In those centuries, the scientific nature of astronomy became incredibly important, along with the construction of telescopes to observe the heavens. Those scientists contributed to the rise of astronomy as a specialized science that we know and rely upon today. 

Edited by Carolyn Collins Petersen.