what is his profession?
An astronomer, physicist and engineer.
Galileo Galilei
Galileo di Vincenzo Bonaiuti de' Galilei (; 15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath, from Pisa. 
define unit of force using second law of motion UNANSWERABLE how does one define force? It is any interaction that, when unopposed, will change the motion of an object. who was the first to define it? The models regarding this were proposed by early thinkers which were corrected by Galileo Galilei, Sir Isaac Newton, and Einstein. where is the first person from? Pisa (then part of the Duchy of Florence), Italy.
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Galileo Galilei [SEP] Introduction
His contributions to observational astronomy include the telescopic confirmation of the phases of Venus, the observation of the four largest satellites of Jupiter, the observation of Saturn's rings, and the analysis of sunspots. Galileo's championing of heliocentrism and Copernicanism met with opposition from within the Catholic Church and from some astronomers. The matter was investigated by the Roman Inquisition in 1615, which concluded that heliocentrism was "foolish and absurd in philosophy, and formally heretical since it explicitly contradicts in many places the sense of Holy Scripture".