In Ptolemy’s geocentric theory of the Solar System, Venus could not go through the complete set of phases observed by Galileo. False True
The correct answer and explanation is:
Correct Answer: True
In Ptolemy’s geocentric theory of the solar system, Venus could not go through the complete set of phases observed by Galileo.
Ptolemy’s geocentric model placed Earth at the center of the universe. In this model, all planets, including Venus, orbited Earth in complex paths involving epicycles to account for their observed motions. According to this theory, Venus’s epicycle was always located between Earth and the Sun. This meant that Venus could only appear in positions close to the Sun in the sky, and from Earth’s perspective, it could only show a limited range of phases. Specifically, Venus would always be seen in crescent or new-like phases because it would never be on the far side of the Sun relative to Earth.
However, in 1610, Galileo used a telescope to observe Venus and discovered that it exhibited a full set of phases similar to the Moon — including gibbous and full phases. This observation was inconsistent with Ptolemy’s geocentric model but perfectly explained by the heliocentric model proposed by Copernicus. In the heliocentric system, Venus orbits the Sun. As Venus moves around the Sun, different portions of its day side become visible from Earth, resulting in the full set of phases.
Galileo’s discovery was one of the major blows to the geocentric theory and served as strong evidence for the heliocentric model. It showed that Venus sometimes lies on the far side of the Sun, which is only possible if Venus orbits the Sun, not Earth. This finding significantly contributed to the Scientific Revolution and the eventual rejection of the Ptolemaic model. Therefore, it is correct to state that in Ptolemy’s geocentric theory, Venus could not go through the complete set of phases observed by Galileo.