Galileo Galilei (15.02.1564-8.01.1642) was an outstanding Italian physicist and astronomer, one of the founders of exact natural science and a member of the Accademia dei Lincei (1611). He was born in Pisa. In 1581 he entered the University of Pisa, where he studied medicine. But, having become absorbed in geometry and mechanics, and in particular in the writings of Archimedes and Euclid, he left the university with its scholastic lectures and returned to Florence, where for four years he studied mathematics on his own. From 1589 he was professor at the University of Pisa, in 1592—1610 at the University of Padua, and later court philosopher to Duke Cosimo II de' Medici. [Taken from the site астрономия.рф]. He had a considerable influence on the development of scientific thought. It is from him that physics as a science takes its beginning.
Humanity owes to Galileo two principles of mechanics which played a large part in the development not only of mechanics but of the whole of physics. These are the well-known Galilean principle of relativity for rectilinear uniform motion and the principle of the constancy of the acceleration of gravity. Starting from the Galilean principle of relativity, I. Newton arrived at the concept of an inertial frame of reference, while the second principle, connected with the free fall of bodies, led him to the concept of inertial and gravitational mass. A. Einstein extended Galileo's mechanical principle of relativity to all physical processes, and in particular to light, and drew from it consequences about the nature of space and time (the Galilean transformations are then replaced by the Lorentz transformations). The combination of the second Galilean principle, which Einstein interpreted as the principle of the equivalence of inertial forces and gravitational forces, with the principle of relativity led him to general relativity. Galileo established the law of inertia (1609), the laws of free fall, of the motion of a body on an inclined plane (1604 — 09) and of a body thrown at an angle to the horizon, and discovered the law of the composition of motions and the law of the constancy of the period of oscillation of a pendulum (the phenomenon of the isochronism of oscillations, 1583). Dynamics takes its beginning from Galileo. In July 1609 Galileo constructed his first spyglass — an optical system consisting of a convex and a concave lens — and began systematic astronomical observations. This was the second birth of the spyglass, which after nearly 20 years of obscurity became a powerful instrument of scientific knowledge. Galileo can therefore be considered the inventor of the first telescope. He improved his spyglass quite quickly and, as he wrote in time, “built myself an instrument so wonderful that with its help objects seemed almost a thousand times larger and more than thirty times nearer than when observed with the naked eye”. In the treatise “The Starry Messenger”, which appeared in Venice on 12 March 1610, he described the discoveries he had made with the telescope: the detection of mountains on the Moon and of four satellites of Jupiter, and the proof that the Milky Way consists of a multitude of stars. The creation of the telescope and his astronomical discoveries brought Galileo wide fame. He soon discovered the phases of Venus, spots on the Sun and so on. Galileo set up the manufacture of telescopes at his own home. By changing the distance between the lenses he also produced a microscope in 1610-14. Thanks to Galileo, lenses and optical instruments became a powerful tool of scientific research. As S. I. Vavilov noted, “it was from Galileo that optics received the greatest stimulus for its further theoretical and technical development”. Galileo's optical research also concerned the theory of colour, questions of the nature of light and physical optics.
The idea that the speed of propagation of light is finite, and the design (1607) of an experiment to determine it, belong to Galileo. Galileo's astronomical discoveries played an enormous part in the development of the scientific world view; they gave entirely clear evidence of the correctness of Copernicus's teaching and of the error of the system of Aristotle and Ptolemy, and they contributed to the victory and the establishment of the heliocentric system of the world. In 1632 the well-known “Dialogue Concerning the Two Chief World Systems” appeared, in which Galileo defended the heliocentric system of Copernicus. The publication of the book enraged the churchmen; the Inquisition accused Galileo of heresy and, having staged a trial, forced him to renounce the Copernican teaching publicly, and it placed a ban on the “Dialogue”. After the trial in 1633 Galileo was declared a “prisoner of the Holy Inquisition” and was obliged to live first in Rome and then in Arcetri near Florence. Galileo did not, however, give up his scientific work: before his illness (in 1637 Galileo finally lost his sight) he completed the work “Discourses and Mathematical Demonstrations Relating to Two New Sciences”, which summed up his research in physics. He invented the thermoscope, which is the prototype of the thermometer, constructed (1586) a hydrostatic balance for determining the specific gravity of solid bodies, and determined the specific gravity of air. He put forward the idea of using a pendulum in clocks. His research in physics also concerned hydrostatics, the strength of materials and so on.
Humanity owes to Galileo two principles of mechanics which played a large part in the development not only of mechanics but of the whole of physics. These are the well-known Galilean principle of relativity for rectilinear uniform motion and the principle of the constancy of the acceleration of gravity. Starting from the Galilean principle of relativity, I. Newton arrived at the concept of an inertial frame of reference, while the second principle, connected with the free fall of bodies, led him to the concept of inertial and gravitational mass. A. Einstein extended Galileo's mechanical principle of relativity to all physical processes, and in particular to light, and drew from it consequences about the nature of space and time (the Galilean transformations are then replaced by the Lorentz transformations). The combination of the second Galilean principle, which Einstein interpreted as the principle of the equivalence of inertial forces and gravitational forces, with the principle of relativity led him to general relativity. Galileo established the law of inertia (1609), the laws of free fall, of the motion of a body on an inclined plane (1604 — 09) and of a body thrown at an angle to the horizon, and discovered the law of the composition of motions and the law of the constancy of the period of oscillation of a pendulum (the phenomenon of the isochronism of oscillations, 1583). Dynamics takes its beginning from Galileo. In July 1609 Galileo constructed his first spyglass — an optical system consisting of a convex and a concave lens — and began systematic astronomical observations. This was the second birth of the spyglass, which after nearly 20 years of obscurity became a powerful instrument of scientific knowledge. Galileo can therefore be considered the inventor of the first telescope. He improved his spyglass quite quickly and, as he wrote in time, “built myself an instrument so wonderful that with its help objects seemed almost a thousand times larger and more than thirty times nearer than when observed with the naked eye”. In the treatise “The Starry Messenger”, which appeared in Venice on 12 March 1610, he described the discoveries he had made with the telescope: the detection of mountains on the Moon and of four satellites of Jupiter, and the proof that the Milky Way consists of a multitude of stars. The creation of the telescope and his astronomical discoveries brought Galileo wide fame. He soon discovered the phases of Venus, spots on the Sun and so on. Galileo set up the manufacture of telescopes at his own home. By changing the distance between the lenses he also produced a microscope in 1610-14. Thanks to Galileo, lenses and optical instruments became a powerful tool of scientific research. As S. I. Vavilov noted, “it was from Galileo that optics received the greatest stimulus for its further theoretical and technical development”. Galileo's optical research also concerned the theory of colour, questions of the nature of light and physical optics.
The idea that the speed of propagation of light is finite, and the design (1607) of an experiment to determine it, belong to Galileo. Galileo's astronomical discoveries played an enormous part in the development of the scientific world view; they gave entirely clear evidence of the correctness of Copernicus's teaching and of the error of the system of Aristotle and Ptolemy, and they contributed to the victory and the establishment of the heliocentric system of the world. In 1632 the well-known “Dialogue Concerning the Two Chief World Systems” appeared, in which Galileo defended the heliocentric system of Copernicus. The publication of the book enraged the churchmen; the Inquisition accused Galileo of heresy and, having staged a trial, forced him to renounce the Copernican teaching publicly, and it placed a ban on the “Dialogue”. After the trial in 1633 Galileo was declared a “prisoner of the Holy Inquisition” and was obliged to live first in Rome and then in Arcetri near Florence. Galileo did not, however, give up his scientific work: before his illness (in 1637 Galileo finally lost his sight) he completed the work “Discourses and Mathematical Demonstrations Relating to Two New Sciences”, which summed up his research in physics. He invented the thermoscope, which is the prototype of the thermometer, constructed (1586) a hydrostatic balance for determining the specific gravity of solid bodies, and determined the specific gravity of air. He put forward the idea of using a pendulum in clocks. His research in physics also concerned hydrostatics, the strength of materials and so on.