Galileo Galilei is one of the most famous scientists and astronomists of all times. Galileo Galilei lived more than 400 years ago. He was born on February 15, 1564 in Pisa, Italy and died at age 77 near Florence, Italy on January 8, 1642 after suffering from a fever and heart palpitations. He was blind at the time of his death. Galileo is known for his work as an astronomer, physicist, engineer, philosopher, and mathematician.Galileo was the oldest of six children. Two of his five siblings died in infancy. His father, Vincenzo Galilei, was a musician (lutenist), composer and music theorist. Galileo learned from his father and became an accomplished lutenist. His youngest brother, Michelangelo, also became a noted lutenist and composer. When Galileo was eight years old, his family moved approximately 50 miles from Pisa to Florence, Italy. Galileo attended a monastery school at Vallombrosa, near Florence, in his teens. In 1581 he began attending the University of Pisa to study medicine but never finished because he was sidetracked by mathematics. He loved mathematics and decided to make mathematical subjects and philosophy his professions, against the protests of his father. Galileo was born in a time when most common people lived in thatched roofed houses with dirt floors. They cooked in the kitchen with a big kettle that hung over the fire. They ate mostly vegetables and did not get much meat. There was no electricity or running water in their houses. People did not take baths very often and their towns were polluted with garbage and sewage. Consequently, they were plagued with diseases. Florence, Italy was the seat of artistic, humanistic, technological and scientific flowering known as the Renaissance. Tremendous innovations were made in the fields of mathematics, medicine and engineering during this time. The Roman Catholic church had a lot of power and influence. Despite being a devout Roman Catholic, Galileo fathered three children out of wedlock with Marina Gamba. They had two daughters, Virginia and Livia, and a son, Vincenzo. Because of their illegitimate births, their father considered the girls unmarriable. They later became nuns, and stayed nuns for the rest of their lives. Vincenzo was legitimated by his father in 1619. Like his grandfather Vincenzo Galilei, the younger Vincenzo became a lutenist.Galileo is referred to as “The Father of Astronomy.” He, was the first person to use a telescope to study the skies. He discovered Jupiter’s four larger moons in 1610. Their original names were Io, Europa, Ganymede, and Callisto. They were later renamed the Galilean satellites (moons) in honor of Galileo. Galileo discovered the rings of Saturn, new stars and studied sun spots. He observed the phases of Venus. He studied many other phenomena.Galileo invented many mechanical devices such as the compass and thermometer, but perhaps his most famous invention was the advancement of the telescope. Galileo made his first telescope in 1609, modeled after telescopes produced in other parts of Europe that could magnify objects. He learned the art of lens grinding which helped him produce increasingly powerful telescopes. He improved the instrument so much that it could magnify up to 3X which helped him have a sharp vision of the moon and its surface. It was through Galileo’s telescope that the moon’s rocky and uneven surface became known. He later improved on this to make telescopes with around 30X magnification. Galileo made major contributions to the world of physics and is known as “The Father of Physics.” He did theoretical and experimental work on the motions of bodies. He conducted many experiments with pendulums. He claimed that a simple pendulum swing always takes the same amount of time, regardless of size and weight. Galileo is lesser known, but still credited with, being one of the first to understand sound frequency. In 1638, he described a simple experiment using lanterns to measure the speed of light. It was documented by Galileo’s pupil, Vincenzo Viviani, that Galileo had also experimented with gravity. Galileo dropped balls of the same material, but different masses, from the Leaning Tower of Pisa to demonstrate that their time of descent was the same without regard to their size and weight. This was contrary to what Aristotle had taught: that heavy objects fall faster than other ones, in direct proportion to weight. Also in his investigations of falling bodies Galileo determined that the acceleration of these bodies is constant. This unique property of gravity was one of the motivations for Einstein’s general theory of relativity. In 1632, Galileo published a book that stated, among other things, that the Heliocentric Theory of Copernicus was correct. In Galileo’s time most educated people believed in the Aristotelian geocentric view that the earth was the center of the universe and that all heavenly bodies revolved around the earth. The Heliocentrism theory was that the earth and planets revolved around the sun. The catholic church rejected this thinking based on bible references that said, “the lord set the earth on its foundations; It can never be moved,” and “the sun rises and sets and returns to its place.” The church claimed that Galileo and his followers were attempting to reinterpret the Bible. The church believed they were they only ones allowed to interpret scriptures and that Galileo’s attempt to reconcile scriptures with his findings was a threat to the church and their power. In October 1632, Galileo was found guilty of heresy by the tribunal of the holy office in Rome. They sent him to exile in Siena and finally in December 1633, he was sentenced to house arrest to his villa in Arcetri in the hills above Florence where he spent the rest of his life. He continued his work including the writing of books even after he became blind by working with a young student, Vincenzo Viviani, who was with him until he died. It was only in the 20th century that several Popes acknowledged the work and contribution of Galileo in the field of astronomy. His inventions, from compasses and balances to improved telescopes and microscopes, revolutionized astronomy and biology. Galileo is recognized for the thoughtful and inventive experimentation that pushed the scientific method toward its modern form.