Final answer:
The 'Ptolemaic model' is the correct answer, where the 'geocentric model' places Earth at the center with celestial bodies revolving around it in complex circular paths.
Step-by-step explanation:
The statement, 'Half stars were above the horizon and half below,' is referring to the Ptolemaic model of the universe. The correct answer is 'd) Ptolemaic model.' According to Ptolemy's view, the geocentric model depicts Earth at the center, with the Moon, planets, the Sun, and stars revolving around it.
This was widely accepted until the Copernican heliocentric model challenged it by placing the Sun at the center of the solar system. The Ptolemaic system is notable for its use of complex circular paths, also known as epicycles, to improve its accuracy in predicting celestial motions.
Despite the Ptolemaic model's descriptive nature, it did not provide explanations for the causes of celestial motions. This contrasts with the Copernican model, which later incorporated laws of physics, including Newton's universal law of gravitation, to clarify these causes more accurately. Hence, the Ptolemaic model, while intricate and historically significant, was ultimately superseded by a heliocentric understanding of the solar system.
Therefore the correct answer is 'd) Ptolemaic model.