Final answer:
Galileo's discovery that the Earth revolves around the sun rather than standing at the center of the universe is an example of heliocentrism.
Step-by-step explanation:
The correct answer is option a: Heliocentrism.
In the past, ancient astronomers believed in a geocentric model, which placed Earth at the center of the universe and everything revolved around it. However, with the help of telescopic observations and experimental physics, Galileo discovered that the Earth actually revolves around the sun, known as the heliocentric model. This revolutionary idea challenged the prevailing belief at that time and marked a significant turning point in our understanding of the cosmos.