History of Astronomy: Part 1

Before we can learn about scientific advances made in astronomy in ancient times, we must first discuss why people in the past were curious and wanted to learn about the cosmos. For starters, astronomical observations helped them keep track of time and seasons, and it aided them in navigation as well. For example, people in ancient central Africa (6500 BC) could predict seasons from the orientation of the crescent moon. In addition, ancient Egyptians used an Egyptian obelisk– a device that assisted Egyptians to observe the shadow of the device, which helped them determine the time of day. Furthermore, Stonehenge (completed around 1550 BC) in England helped determine the days of the summer solstice and winter solstice.

The Geocentric Model

The Greeks were the first people known to make models of nature. A scientific model is a conceptual representation of a natural phenomena used to explain and predict the phenomena’s behavior. It does not have to be a physics model– for example, many mathematical equations can be used as models. They tried to explain patterns in nature without resorting to myth or the supernatural. In Astronomy specifically, they tried to explain planetary motion. To do so, Plato and Aristotle created and added to the geocentric model. The geocentric model was a theoretical model that placed Earth at the center of the Universe and predicted that because the heavens must be perfect, objects must move in perfect spheres or circles. This model had many inaccuracies, but one specific inaccuracy that led to a new model was the fact that it could not explain retrograde motion. Retrograde motion is when a planet appears to move backwards (west to east) in the sky (from Earth’s perspective) due to the fact that Earth is passing that planet in orbit. According to the geocentric model, because the stars and planets must move in perfect motion, they only moved in one direction, but when planets moved in retrograde motion, it clearly went against the theory.

The Copernican Revolution

Copernicus was the first to propose a sun-centered model (published in 1543, also known as the Copernican model), which helped determine the layout of the solar system– in terms of planetary distances. But, this model was no more accurate than the geocentric model because it was built on the theory that everything moved in perfect circle, and thus it could not explain retrograde motion. Eventually Kepler found evidence to determine that objects in outer space moved in perfect circles, and instead determined that they move in ellipses. An ellipse is an elongated circle with two foci, instead of one focus (like a circle). In addition, Galileo helped overcome major objections that people had to the Copernican model, which eventually helped transition people from using the geocentric model to the sun-centered model.

---

Thank you for reaching the end of this blog. Be sure to check out other blogs as well to continue to learn more about astronomy! Don't forget to like and share! Stay tuned for our next blog post and as always, keep gazing skywards!