Tycho Brahe (1546 – 1601) after studying at various European universities, returned to Denmark, his homeland, where he was appointed Astronomer Royal. Thanks to the help of the monarch, he managed to build an observatory on the island of Wen in the Sund Strait, in the Baltic, the Uraniborg observatory that became one of the centers of science of the time. When he lost the king’s favor he emigrated to Prague, where he completed his work and died. The importance of him for astronomy lies in the systematization of the astronomical measurements carried out so far. In his “Rudolphine Tables” he summarized the observations that can be made on the stars without optical instruments. He also demonstrated the astronomical – supralunar – and not meteorological – sublunar – character of the “novae” and of the comets, thereby refuting the Aristotelian assertion, dominant in his time, of the perfection and immutability of the heavens. The Attic system Tycho Brahe proposed a model of the planetary system in which the EARTH WAS THE CENTER, THE Moon and the Sun moved around it, and the other planets moved around the Sun. Tycho Brahe achieved with his conciliar model the Bible , the laws of motion of Aristotelian physics and the absence of stellar parallax. At the same time his system is mathematically equivalent to that of Copernicus. Tycho’s model forces one to set aside the crystalline spheres that until now had been thought to drag the planets along their orbits. Tycho’s model was quickly accepted by the Jesuits, who explained it by mission lands. The geo – heliocentric system has antecedents in ancient astronomy (Heraclides and Ecfantos) and medieval (Juan Escoto Eriúgena) but Copernicus, although he knew it, ignored it.

**Johannes Kepler **

Kepler was born in Well in 1575 and died in Regensburg in 1630. He studied Astronomy with the Copernican Mästlin. Besides being a great mathematician, he was an astronomer and astrologer for different European monarchs. He obtained more resources from this last activity than from his scientific knowledge. His life was a continual disgrace. His mother was accused of witchcraft, his wife died insane, seven of his children died. All that made him say that he took refuge in heaven to flee from this Earth. In 1600 he met Tycho Brahe. In 16009 he published “Astronomy nova” and in 1619 “Armonices Mundi”, works that are the foundations of scientific Astronomy. Kepler succeeded in transforming the heliocentric conception of Copernicus into an exact mathematical model. However, his scientific theories cannot be considered entirely correct.

**The first two laws of Kepler **

Although Kepler discovered the second law before the first, when he studied the irregularities of up to 8 minutes that the planet Mars presented with respect to the Copernican and Attic systems, in his book “Astronomy Nova” (1619) they appear in usual order. 1st. The planets move in elliptical orbits with the Sun in one of its foci. 2nd. The line connecting the center of a planet to the Sun sweeps out equal areas in equal times.

**Kepler spheres **

Kepler was an astronomer and mathematician fascinated by the geometry of Euclid. He saw in the Universe the work of a divine creator, the Perfect Geometer. In an effort to discover this geometry, he spent much of his life trying to associate the 5 Pythagorean solids with the orbits of the planets around the Sun, nesting one inside the other, in what he called his “cosmic mystery”, published in 1596. Based on the dodecahedron and the spheres that arise from the intersection of its diagonals, he was able to locate the orbits of some planets. Kepler tried to give an explanation to the distances of the planetary orbits proposed by Copernicus, but attributing their origin to the Perfect Geometer, since he did not agree with the vision of Copernicus, which seemed lacking in harmony and, nevertheless, the presence of the great Geometer, assumed that it must contain a perfect geometry. As more planets were discovered in the Solar System, this hypothesis fell into disrepute, but his most important legacy was the idea of a universe that can be exp