416 years ago today, on August 25, 1609 (July 26, 1609 lunar calendar), Galileo Galilei showed off his first refracting telescope at the Venice Parliament. August 25, 1609 Italian astronomer Galileo Galilei showed off his first refracting telescope at the Venice Parliament. Four hundred years ago, mankind changed our understanding of the universe forever. On August 25, 1609, an Italian mathematician named Galileo Galilei demonstrated his new telescope to merchants in Venice. Soon after, he turned his telescope to the sky. He saw the mountains casting shadows on the moon, and he realized that the moon, like the earth, is also a complex world. He saw a constellation of Jupiter's moons - very different from what the church taught - orbiting another celestial body. He saw that Venus, like the moon, had a profit and loss phenomenon, indicating that Venus revolved around the sun, not the earth, which was even more contrary to what the priest said. He saw sunspots, proving that the sun itself was not a perfect celestial body as the Greek cosmology accepted by the Church. But he also saw something else, which is now often forgotten. He saw the Milky Way, a cloud-like strip that spans the sky, made of stars. That observation was the first to suggest that not only was the earth not the center of everything, but that the vastness of the universe was far beyond the comprehension of people of that era. And the universe has been growing and getting older ever since. Astronomers' latest estimate is that the universe is about 13.70 billion years old, three times the age of the Earth and 100,000 times the lifespan of modern humans as a species. Just how big the universe is is unknown. Its age and finite speed of light mean that no astronomer can go beyond 13.70 billion light years. Yet the universe may be bigger than that. And reality is not necessarily limited to this one universe. Physics, closely tied to astronomy, tells us that the objects we call the universe, though vast, may be just one of countless similar structures that follow slightly different laws. For lack of a better description, they are currently called the multiverse. Galileo's contemporaries believed that the universe, a crystal ball, contained planets and stars, and that these stars represented the edge of the universe. The collapse of this theory (along with Darwin's idea of natural selection) became the greatest revolution in human understanding of the self. Galileo lived in a world where the level of cognition was limited. The Greeks had a clear understanding of the size of the earth and its distance from the moon, and medieval readers of Greek writings carried on these ideas. Such distances are the level that human imagination has long been able to achieve. It was easy to believe that the universe was as big as the heart. Now, however, in the face of modern cosmology, it is harder to argue whether this was motivated by human self-interest, let alone multicosmology. Four hundred years later, the heirs to Galileo's ideas are no longer considered dangerous revolutionaries. They will meet this week in Rio de Janeiro under the auspices of the International Astronomical Union. But their discoveries were as transformative as Galileo's, ranging from the possibility of alien life on planets around other stars to dark matter and the unknown nature of energy as an important substance in real life. Modern humans may be more attuned to the idea of a sudden change in humanity's place in the universe than medieval humans were. But this should not blind people to the wonders of the cosmic conjecture. Comment: Great invention that changed humanity's understanding of the universe.