Understanding Relative Distances in Astronomy

Continuing from our previous discussion on distances and sizes, we now explore how ancient astronomers estimated the relative distances between the Earth, Moon, and Sun. Our focus is on Aristarchus of Samos, who lived from 310 BC to 230 BC. Aristarchus used simple geometry to estimate these distances and relative sizes. He observed the phases of the Moon, specifically the first quarter, forming a right triangle between the Earth, Moon, and Sun, with the Moon at the 90-degree angle. By measuring the angle between the Moon and the Sun at first quarter phase, Aristarchus estimated it to be about 87 degrees (it is actually closer to 89 degrees and 51 minutes). Using this angle, he calculated the Sun’s distance to be approximately 19 times that of the Moon’s distance from Earth. This indicated that the Sun was much farther away and therefore much larger than the Moon. Additionally, by timing the duration of lunar eclipses, he deduced that the Moon’s size was about half that of Earth. Although his measurements were not precise by modern standards, Aristarchus made significant strides in understanding the relative sizes and distances, suggesting that the Sun was significantly larger than both Earth and Moon. These observations and calculations were pioneering efforts that paved the way for future astronomical methods. Although Aristarchus’s measurements had considerable errors, his work laid the groundwork for understanding celestial distances and the scale of our solar system. Our next discussion will delve into the historical debate about the heliocentric model and the evidence supporting Earth’s motion around the Sun, a fundamental question that has shaped modern astronomy.

[garethdean]

We must also consider the school of corpocentrism, the belief that the universe is centered on a single body, that of the corpocentrist themself. It's always been remarkably popular.

[professorsogol]

". . . various locations along the equator"?? Neither Aswan (Syene) nor Alexandria are on the equator.