Aristarchus was able to prove that … A) the Earth orbits around the Sun B) the circumference of the Earth is about 40,000 km C) the Sun orbits around the Earth D) the Sun is larger than the Earth
The correct answer and explanation is:
Correct Answer: D) The Sun is larger than the Earth
Explanation (300 words):
Aristarchus of Samos was an ancient Greek astronomer and mathematician who lived around 310–230 BCE. He is best known for being one of the earliest proponents of a heliocentric model of the solar system—suggesting that the Earth revolves around the Sun. However, he was not able to prove this idea during his time, and it remained largely unaccepted until Copernicus revived it over a millennium later.
One of Aristarchus’s most significant achievements, which he was able to demonstrate, was that the Sun is much larger than the Earth. He reached this conclusion through geometric reasoning and observations during the phases of the Moon. Specifically, he used the angle between the Sun and Moon during a half-moon phase to estimate the relative distances and sizes of these celestial bodies.
Aristarchus assumed that the Moon reflects sunlight and that during the first or last quarter phase, the angle between the Earth, Moon, and Sun forms a right triangle. Using this geometry, he attempted to measure the angle between the Moon and the Sun and, based on that, deduced that the Sun must be much farther away than the Moon—and, consequently, much larger.
Although his measurements were not very accurate due to the limitations of ancient observational tools, his reasoning led to the correct qualitative conclusion: the Sun is vastly larger than the Earth. This realization may have influenced his heliocentric thinking—if the Sun is larger and farther away, it may make more sense for the Earth to orbit it, rather than the other way around.
Therefore, while Aristarchus proposed (but did not prove) that the Earth orbits the Sun, what he did convincingly argue with the evidence and tools available at the time was that the Sun is larger than the Earth.