Final answer:
Based on observations, Earth's motion relative to the Sun can be explained with Kepler's Second Law, which describes its orbital velocity, and Earth's daily west-to-east rotation, which is evident from the cycle of day and night.
Step-by-step explanation:
Rules Relating Earth's Motion to the Sun
Upon observing the motion of Earth and the Sun, we can establish two rules based on Kepler's Laws of Planetary Motion and the daily rotation of Earth.
The first rule involves Kepler's Second Law, which states that a line drawn from Earth to the Sun sweeps out equal areas during equal intervals of time. This implies that when Earth is closer to the Sun in its elliptical orbit during perihelion, it travels faster, and it slows down when it's further away at aphelion.
The second rule concerns Earth's rotation. By marking points on a representation of Earth, such as an apple, and simulating Earth's rotation from west to east, it can be shown that the rotation is responsible for the daily cycle of day and night. Additionally, the correction needed while observing sunspots to account for Earth's orbital motion illustrates Earth's motion around the Sun and not the Sun rotating around Earth.
If we consider Earth as the inertial frame of reference, it appears that the Sun orbits around Earth. Conversely, if we take the Sun as the inertial frame, we observe that Earth orbits the Sun. These perspectives change depending on the chosen frame of reference, but modern science supports the heliocentric model, where Earth orbits the Sun.