Galileo Galilei was born on February 15, 1564.
He was not just one of the giants in the first phase of modern science: he is reckoned as its founder. But he also got into trouble with ecclesiastical authorities, as much for espousing views about the world then declared to be heretical, as by his intransigence which struck some as arrogance.
Galileo went to the university to become a physician. He heard a lecture on mathematics, and fell in love with the subject. He was stirred to explore the world by observing it, rather than by speculating on it.
One of his biographers says that Galileo measured the time of swing of a pendulum by observing swinging chandeliers in church and using his pulse to measure time. [Tourists are shown the pendulum in Pisa which Galileo is said to have observed, though this one was installed five years later. But that is how tourism-history is constructed.] He analyzed the motion of projectiles, studied bodies slide down inclined planes, initiated the quantitative study of motion, and declared that the laws of nature are written in the language of mathematics. He was one of the first to formulate the law of inertia: we don’t need a force to keep bodies in motion. He turned the telescope skyward, and brought to human knowledge aspects of the heavens which none before him had seen or suspected: such as craters on the Moon, the grainy structure of the Milky Way, and four satellites of Jupiter. He detected spots on the sun, and theorized that tides resulted from the orbital rush of the Earth around the Sun. He served the new astronomy by propagating the Sun-centered model through a popular book.
Galileo was God-fearing and faithful, attended mass on Sundays, visited a place of pilgrimage to express thanks for recovery from an illness, and attributed to God the wonder of the phenomenal world. But he was stubborn in his conviction that truths about the physical world can be known only through observation and experiment, and he doubted that the Holy Book can be regarded as an authority in the mathematical sciences. Like al-Farábi of the Islamic tradition, he argued that sacred books must not be taken literally, but only metaphorically. Fortunately for the West, its al-Ghazâlîs lost the battle in curbing freedom of thought so essential for the progress of science.
Galileo befriended cardinals and popes, and they respected him. But he also made enemies among scholars and clerics who rejected the heliocentric worldview. They saw in Galileo a threat to long-cherished scriptural cosmography. He had but scant respect and much contempt for the unscientific authorities who dictated worldviews.
When he was almost seventy, he was brought to trial: not for offense against God, but for propagating the idea that the earth was moving around the Sun. He conceded he had been arrogant in writing the book, and promised not to engage in heresies any more. Because he pronounced the mea culpa, and also because of his age and stature, he was spared the torture chamber, only sentenced to house arrest and ordered to read regularly passages from the Bible. If it is difficult for us to imagine such a punishment, we may be happy that some societies have made progress in the matter of intellectual freedom and have been freed from the tyranny of those who presume to speak for the Almighty.
Galileo was close to his children: most of all to his older daughter Maria Celeste who wrote to him regularly from the nunnery to where she had retired at an early age.
His inquiring, insightful, and inventing mind enriched human knowledge and creativity in ways that few others in human history have achieved.