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. This is true because the geocentric model placed Earth at the center of the universe, with the Sun and all other planets, including Venus, orbiting around Earth. According to this model, Venus always remained near the Sun in the sky and was always between Earth and the Sun or just slightly to the side.
Under the Ptolemaic model, Venus’s orbit was described using epicycles and deferents, which were circular paths upon which the planets moved. These were mathematical tools used to explain the apparent motion of the planets, especially retrograde motion, without accepting that the planets orbited the Sun. Within this system, Venus could only appear as a crescent or new phase, because it was never positioned on the far side of the Sun from Earth. That positioning is necessary for Venus to appear in a gibbous or full phase.
However, when Galileo observed Venus through his telescope in the early 1600s, he found that it showed a complete set of phases, similar to the Moon. These included crescent, quarter, gibbous, and full phases. This could not be explained by the Ptolemaic system. Instead, it strongly supported Copernicus’s heliocentric model, in which Venus orbits the Sun. In this model, Venus is sometimes between Earth and the Sun (showing crescent phases) and sometimes on the far side of the Sun (showing gibbous and full phases), which matched Galileo’s observations.
Galileo’s discovery was a major blow to the geocentric theory and helped convince the scientific community to move toward the heliocentric model, where planets, including Earth, orbit the Sun.