Understanding Celestial Reference Systems and Simplifying Planetary Orbits

When observing the Sun, you might notice Earth's orbit around it; on the other hand, from Earth, the opposite appears to be true. Additionally, you could consider the center of mass for the Earth-Sun system or the entire solar system, around which both Earth and the Sun revolve. The possibilities are virtually limitless. Without deciding on a specific 'reference system' (essentially choosing an observation point for these celestial bodies), you may encounter ambiguity, as your selection is entirely arbitrary.

Understanding the popularity of planets orbiting the Sun

The reason this concept is so widely accepted is that it's generally more convenient. For instance, it simplifies the description of planetary orbits, which become elliptical with precession - often approximated as simple circles in school. However, observing Venus' orbit from Earth rather than the Sun would complicate matters:

The illustration above demonstrates that Venus' trajectory is far from a perfect circle. It's important to note that several assumptions were made in creating this graph, such as Venus and Earth having perfect circular, concentric, coplanar orbits relative to the Sun, and their orbital periods having an exact 8:13 ratio.

For further exploration of this topic, consider using a free and easy-to-use online simulator that employs the geometric concept of epitrochoid to recreate planetary motion curves in geocentric perspective and beyond for various celestial bodies in the solar system (allowing you to generate images similar to the one shown above).

Source: Cambridge.