First Heliocentrist
A Greek Astronomer’s Forgotten Heliocentric Breakthrough
We typically associate Copernicus as the first person to determine that the Earth revolves around the Sun, rather than the other way around. However, almost 2000 years earlier, around 310–230 BC, a Greek astronomer named Aristarchus had reached a similar conclusion after attempting to estimate the distance between the Earth and the Sun based on observations of the Moon.
Aristarchus observed lunar eclipses, noting the positions and Earth’s shadow on the Moon, and applied geometric principles to these observations. One of his key insights involved measuring the angle between the Sun and the Moon when the Moon was exactly half-illuminated, known as the first or last quarter moon, when there is aright angle between the Earth, Sun, and Moon.
From these observations, Aristarchus concluded that the Sun was much farther away from Earth than the Moon was—about 20 times. Although this figure was a significant underestimate—the Sun is actually about 400 times farther than the Moon—his method was sound, and his conclusion that the Sun was much more distant than the Moon was correct. Moreover, his calculations suggested that the Sun was much larger than Earth, which was crucial for supporting the heliocentric theory, as it would make more sense for Earth to rotate around the bigger object.
However, due to the dominant philosophical and astronomical views of his time, Aristarchus’s heliocentric theory was not widely accepted, and his works were largely forgotten until the Renaissance, when they were revived by Copernicus. Sometimes, even if the final calculations are not entirely correct, they still point in the right direction for thinking about an important problem.
Craving more? Check out the source behind this Brain Snack!