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 up there probably since the first cave people existed. The earliest astronomers were priests, priestesses, and other "elites" who studied the movement of celestial bodies to determine celebrations and planting cycles. With their ability to observe and even forecast celestial events, these people held great power among their societies.

However, their observations were not exactly scientific, but more based on a faulty idea that celestial objects were gods or goddesses. Moreover, people often imagined that the stars could "foretell" their own futures, which led to the now-discounted practice of astrology. 

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 taught observers that Earth 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 early observers in history believed the heavens were a giant bowl covering the 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 concentric spheres surrounding Earth.

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 600 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. He said that the planets moved in perfect circles, attached to perfect spheres, that all rotated around the 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 14 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 that Earth and other planets revolved around it. The fact that this idea conflicted with the Holy Roman church's idea (which was largely based on the "perfection" of Ptolemy's theory), 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. But, Copernicus persisted.

The Copernican 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.)

While it was a major step in the right direction, Copernicus’ theories were still quite cumbersome and imprecise. His book, On the Revolutions of the Heavenly Bodies, which was published as he lay on his deathbed, was still 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.

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Greene, Nick. "Trace the Earliest History of Astronomy." ThoughtCo, Jul. 24, 2017, Greene, Nick. (2017, July 24). Trace the Earliest History of Astronomy. Retrieved from Greene, Nick. "Trace the Earliest History of Astronomy." ThoughtCo. (accessed June 17, 2018).