Galileo Galilei (1564-1642). He was a proponent of the Copernican theory, which brought him great conflicts with the Inquisition of Rome, where he was forbidden to continue defending this system. However, it was the theory of transubstantiation referred to the sacrament of the Eucharist, and not geocentric theory, the real heart of the problem. This astronomer who in 1610, upon discovering the four satellites of Jupiter, found the objective verification of the Copernican theory, also discovered the laws of the fall free, inertia, oscillation of the pendulum and the principles of scale in resistance of materials. Modern Physics begins with Galileo, introducing the Scientific Method and by transforming time, from a discrete function to a continuous function. From 1609 he built a telescope and made finds and observations (sunspots, four moons of Jupiter, phases of Venus, lunar mountains, etc.), which he published in 1610 in Siderius Nuncius. With the phases of Venus, he notices the rotation of this planet around the Sun and not Earth.

Among the astronomers of this time we have Simon Marius (moons of Jupiter, detection of the Andromeda nebula in 1612), Christoph Scheiner (first systematic work of sunspots), Johannes Hevelius (observations of the Moon and comets), Christian Huygens (discovery of the ring of Saturn and of Titan the largest satellite of the planet), Giovanni Domenico Cassini (made numerous planetary observations, discovered four satellites of Saturn), Olaus Römer (determination of the speed of the light from the eclipses of the satellites of Jupiter), John Flamsteed (foundation of the Greenwich Observatory in 1675, stellar catalog).

The discovery of the Law of Universal Gravitation allowed, not only to settle the Copernican system but, increase the precision of calculations of lunar orbits and planetary, since the law also took into account the gravitational disturbances between the intervening bodies. In the 18th and early 19th centuries, celestial mechanics developed. There is no computer. Halley calculates the elliptical orbit of the comet in 1682. Kant attributes in 1755 the genesis of the solar system to a mechanical process. Lagrange studies in 1788 the well-known three-body problem and some special cases with solution. Laplace publishes in 1799 his Celestial Mechanics and discovers the invariance of the major axis of the orbits planetary. Leverrier and Adams predict the existence of Neptune by disturbances that Uranus suffers and the planet is discovered in 1846 at the Berlin Observatory. Bessel deduced in 1844, by the disturbances of the proper motion of Sirius, the existence of its unknown companion, who is actually observed in 1862

Also, the instrumental technique matured in the 18th and 19th centuries, as did the Measurement techniques and methods are continually advancing. The first are born stellar catalogs. With the investigations on the solar spectrum and the dark stripes that are named after him (1814), with the creation of spectral analysis by R. W. Bunsen and G. R. Kirchhoff (1895) and with the introduction of photographic methods and photometers in the second half of the 19th century, astrophysics is founded.