Aristarchus of Samos, The Founder of The Heliocentric Theory

Since ancient times, the movement of celestial bodies has captivated humankind. The daily rise and set of the sun, the changing shape of the moon, and the apparent shifting of the stars across the night sky have sparked curiosity, seeking to understand the patterns and causes behind these phenomena. From these observations, humans began to construct various interpretations of how the universe works, though initially still influenced by simple assumptions and beliefs. Amidst these limitations, an ancient Greek thinker emerged who dared to offer a different perspective on celestial movements. He was Aristarchus of Samos, who attempted to explain the order of the universe through a rational approach and thought that was far ahead of his time.

Biography of Aristarchus of Samos

From a young age, Aristarchus pursued scientific knowledge, studying at the Lyceum, an educational institution founded by Aristotle. He also wrote several works on astronomy discussing the motions of celestial bodies. Although his ideas were not immediately accepted in his time, Aristarchus's thinking later became an important foundation for the development of astronomy in later periods. The only surviving work attributed to him is "On the Sizes and Distances of the Sun and Moon," in which he made an early scientific attempt to estimate the dimensions of the solar system, claiming that the Sun was much farther from Earth than the Moon. Although his calculations were ultimately inaccurate, they laid the foundation for future astronomical thought.

The Birth of the Heliocentric Theory

The idea of ​​the origins of the heliocentric theory did not emerge suddenly, but rather stemmed from the thoughts of earlier Greek philosophers. One important figure was Anaxagoras of Clazomenae, who boldly asserted that the light of the Moon was actually a reflection of the Sun, and argued that the Sun was not a god, but rather a celestial body illuminated by its own heat. This view was considered extremely bold for its time, even leading to accusations of heresy and ultimately exile to Lampsacus.

This rational thinking later influenced Aristarchus of Samos's view of the universe. Inspired by the idea that celestial phenomena could be explained logically, Aristarchus began to develop the view that the Earth was not stationary, but rather moved around the Sun. He also continued Philolaus's idea, which had previously proposed that the Earth moved, by adding that the Earth also rotated on its axis. Furthermore, Aristarchus is known as one of the first scientists to attempt to measure the relative sizes of the Sun and the Moon. Although his measurements were not yet accurate by modern standards, his efforts demonstrate that humans at that time had begun to scientifically understand the vast scale of the universe.

The development of astronomical thought continued through the contributions of other Greek figures such as Eratosthenes, who successfully measured the Earth's circumference, Hipparchus, who compiled a star catalog, and Claudius Ptolemy, who developed the geocentric model that dominated for centuries. Even the ideas of Thales of Miletus, Apollonius of Perga, and Aristotle contributed to enriching human understanding of the universe. From this series of thoughts, it is clear that Aristarchus' heliocentric theory was not a standalone idea, but rather part of a long journey of scientific development that has been continuously refined from generation to generation.

Development of Heliocentric Theory

Starting from the basic idea of ​​heliocentrism, Aristarchus of Samos didn't stop at just one idea. He continued to deepen and develop his views through broader observation and reasoning, so that the concept he developed was not just a simple idea, but developed into a more comprehensive understanding of the regularity of the movements of celestial bodies.

1. Size of the Moon He estimated the Moon's size by observing lunar eclipses, when the Moon enters Earth's shadow. From these observations, he concluded that the diameter of Earth's shadow is about 2.5 times the diameter of the Moon. Taking the shadow effect into account, he estimated that the Moon's size is about 1/3.5 of Earth's diameter—a fairly close figure for ancient measurements.

2. Distance to the Moon to calculate the Moon's distance, Aristarchus used a simple method of comparing the size of a small object (such as a coin) to the Moon's appearance in the sky. From this comparison, he estimated that the Moon's distance is about 110 times the Moon's diameter.

3. Distance to the Sun Aristarchus tried to determine the distance to the Sun by observing the phases of the half Moon. He imagined the Earth, Moon, and Sun forming a triangle and then used a geometric approach to estimate their distances. He concluded that the Sun was about 20 times farther away than the Moon, although the actual distance was about 400 times farther.

4. Size of the Sun Using a method similar to measuring the Moon, he estimated the Sun's size based on the comparison of viewing angles. He concluded that the Sun's diameter was very large compared to Earth's, although his results are not yet accurate by modern standards.

5. The Size of the Earth and Its Implications From all these calculations, Aristarchus realized that the Sun was much larger than the Earth. He estimated that the Sun was several times larger than the Earth, which then led to an important thought: a smaller object (the Earth) probably orbited a larger object (the Sun).

Although Aristarchus' measurements were not completely accurate, the mathematical and logical approach he used represented the first step in humankind's scientific understanding of the scale of the universe, and also provided an important basis for the birth of the heliocentric theory.