The Sun-Centered Solar System and Other Baloney
The standard story learned by schoolchildren is that Ptolemy (c. 90–168 CE) thought the Earth was the center of the universe, and everyone agreed, for a long time. Then in 1543, Copernicus came along, said the Sun is at the center, and almost everyone changed their mind, although it took a while.
Well, that's baloney.
For starters, there were some ancients who thought the Sun was at the center. Aristarchus of Samos (c. 310–230 BCE) was one.
Moreover, it's completely okay (i.e. not wrong) to say that the center of the universe is at the center of the Earth. Mathematically, we'd put the origin of our coordinate system at the Earth's center of mass. We could make graphs showing how the positions of the Sun, planets, and stars change over time, in our Earth-centered coordinate system. In fact, people who design Earth-orbiting space missions often do exactly that. It's convenient because near the Earth, the main forces are the gravity of the Earth and atmospheric drag. Other forces, like the gravity of the Sun, or the gravity of the Moon, can be treated as small extras, to be worried-about later, if at all.
If you're studying the motions of the Sun and the planets, then you might put the origin of your coordinates at the center of the Sun, but the math gets complicated. It's easier if you put the origin at the center of mass of the entire system (Sun, Jupiter, Saturn, Earth, etc.).
If you're studying the motions of the stars in the Milky Way galaxy, then you might put your origin at the center of the galaxy.
In general, you can put the origin of your coordinate system anywhere at all. There's no wrong place. There are just more- or less-convenient places, depending on what you're doing. You can put it on the peak of Mount Everest for all I care. In fact, you might even attach it to a spacecraft that travels around the solar system. Why not?
To be fair, Copernicus' idea was more than a mathematical trick. It was a questioning of Earth's central place in the universe. The Earth isn't at the center? Humanity isn't in a special place? It was a big change. It made lots of people unhappy.
Rant complete. Carry on.
References and Suggested Further Reading
The Cambridge Concise History of Astronomy, edited by Michael Hoskin.
The image is of the painting Astronomer Copernicus, conversation with God by Jan Matejko. It's public domain. It was at the Jagiellonian University Museum in Kraków, Poland.
About this Blog
Outer Spacing is a blog about space exploration and development. It's written by Troy McConaghy (@TroyMc on Twitter).