Question

Choose the best answer to each of the following. Explain your reasoning with one or more complete sentences.Which of the following was not a major advantage of Copernicus's Sun-centered model over the Ptolemaic model? (a) It made significantly better predictions of planetary positions in our sky. (b) It offered a more natural explanation for the apparent retrograde motion of planets in our sky. (c) It allowed calculation of the orbital periods and distances of the planets.

Short answer

The major advantage not provided by Copernicus's model was (a) better predictions of planetary positions.

Step-by-step solution

Understand Both Models

The Ptolemaic model is an Earth-centered model where planets and the Sun orbit Earth. In contrast, Copernicus's model is Sun-centered, where planets, including Earth, orbit around the Sun.

Analyze Answer Choices

Evaluate each listed advantage in relation to Copernicus's model. - (a) The Copernican model did not initially make better predictions than the Ptolemaic model because it used circular orbits, which were incorrect. - (b) The Copernican model offers a simpler explanation for retrograde motion as a natural consequence of Earth overtaking other planets in their orbits. - (c) It allowed calculations of orbital periods and relative distances because it placed the Sun at the center, making these measurements more straightforward.

Eliminate Based on Analysis

Based on the analysis, option (a) stands out as it is known the Copernican model's predictions were not significantly better initially due to its assumption of circular orbits. Options (b) and (c) are recognized as actual advantages of the Sun-centered model.

Key concepts

Ptolemaic model

In ancient astronomy, the Ptolemaic model was the prevalent system that described the universe with Earth at its center. This geocentric model, devised by Claudius Ptolemy in the 2nd century AD, suggested that all celestial bodies, including the Sun, moon, stars, and planets, revolve around the Earth.
As it was quite comprehensive for its time, the Ptolemaic model was widely accepted due to its ability to predict the positions of planets in the sky with reasonable accuracy.

• It used a complex system of circles, known as epicycles, to explain the observed planetary movements.
• One significant challenge was explaining the phenomenon of retrograde motion, making the orbital paths of planets appear irregular.

Despite its initially successful predictions, the model was increasingly questioned over the centuries due to its complexity and lack of parsimony.

Sun-centered model

The Sun-centered model, also known as the heliocentric model, was proposed by Nicolaus Copernicus in the 16th century. This revolutionary concept positioned the Sun, rather than Earth, at the center of the universe. Under this model, Earth and other planets orbit around the Sun.
It fundamentally changed our understanding of the cosmos by challenging centuries of geocentric thought.

• This model simplified the explanation of observed celestial phenomena.
• It framed the movement of planets, including Earth, in a more rational and less convoluted manner.

The heliocentric model laid the groundwork for modern astronomy, as later scientists were able to refine and expand upon Copernicus’s ideas.

planetary motion

Planetary motion refers to the movement of planets around a central celestial body, such as the Sun. In the context of our solar system, understanding planetary motion was a challenge across several historical models, like the Ptolemaic and Copernican systems.
Copernicus's Sun-centered model provided a systematic framework to study planetary movements more effectively because it aligned more closely with observed phenomena.

• It explained why planets appear to move backward in the sky, a phenomenon known as retrograde motion, more naturally.
• By considering planets orbiting in larger circles around the Sun, it opened the door to understanding elliptical orbits, thanks to later contributions by Johannes Kepler.

Overall, the understanding of planetary motion has been significantly enhanced by shifting perspective from Earth-centered to Sun-centered.

orbital periods

Orbital periods represent the time a planet takes to complete one full orbit around the Sun. In the heliocentric model, these periods are easier to determine compared to the geocentric model, where such calculations were more convoluted.
Copernicus's model provided a simpler basis for calculating these periods as each planet could be thought to have a regular, predictable path.

• For instance, the orbital period of Earth is about 365.25 days, defining our year.
• Mercury, being close to the Sun, has an orbital period of about 88 days, whereas Neptune, much farther away, takes about 165 Earth years.

The determination of these periods was crucial for improving the accuracy of astronomical predictions and understanding the mechanics of our solar system.

retrograde motion

Retrograde motion is the apparent backward movement of planets as observed from Earth. This puzzling phenomenon occurs because of the relative motion of Earth and the other planets.
The Ptolemaic system required complex constructs, such as epicycles, to account for retrograde motion. In contrast, the Sun-centered model provided a clearer insight.

• In the Copernican model, retrograde motion is explained as an optical illusion described by Earth overtaking another planet in its orbit.
• Imagine Earth moving faster on an inner track while another planet is currently on an outer, slower orbit. To an observer on Earth, this gives the appearance of the planet moving backwards.

By simplifying the explanation of retrograde motion, Copernicus's model debunked many of the geocentric assumptions, paving the way for further exploration into planetary dynamics.