The history of Planetary Sciences (or Planetology), and consequently of Geology
Planetary, is directly linked to the history of Astronomy. Only after centuries of observations, and the advent of instruments that allowed a better visualization of celestial bodies, man was able to differentiate the various types of stars and begin to make inferences about their characteristics and evolution.
According to Évora (1993), Astronomy possibly arose in Babylon, although it is still strongly linked to mythology and mysticism. The earliest records consist of star catalogs from around 1200 BC associated with the Sumerians. The astronomy developed by these people had a strong mythological link, associating stars with deities, and was not concerned with explaining the functioning of the cosmos. This astronomy significantly influenced the astronomy and mythology of the peoples who later inhabited the region, including the Babylonians. The Babylonians not only incorporated the science of the Sumerians, they created a new
observational and empirically based astronomy, and the first philosophical bases about the nature of the Universe (Wikipedia 1). Such ideas were then incorporated by the Greeks, who continued to develop astronomy and cosmology as sciences, now “unlinked[s] from mythology and built[s] on astronomical observations […]” (Évora 1993).
The first astronomical system created by the Greeks was possibly the one developed by the Pythagorean school of thought in the 5th century BC (Wikipedia 1). According to this model, all the stars of the cosmos would be perfect spheres orbiting the Altar of Zeus, the main deity of Greek mythology. Although strongly based on an aesthetic sense that considered the sphere as the most perfect of forms, it established several key concepts for later models (eg the concept of orbits) and the philosophical bases that led to the creation of the heliocentric model.
This model was succeeded by that of Plato, developed in the fourth century BC (Évora 1993), who for the first time was concerned with explaining the motion of the planets. According to him, the planets would be positioned in their own celestial spheres, which moved around the Earth. Aristotle used these ideas as a basis to develop his own model, also centered on Earth. According to the philosopher, all the stars of the cosmos, with the exception of the Earth, would be composed of ether, arranged in two celestial spheres.
The first would be composed of several interconnected mobile planetary spheres, where the planets would be (including the Sun and Moon); the second would contain all the fixed stars, immobile in relation to each other. The Aristotelian model, in turn, was used by Ptolemy as a basis for the development of the Epicycles and Deferent System, which sought to explain hitherto unexplained phenomena (e.g. variations in the brightness of stars). According to this model, the orbits of all the stars could be explained by epicycles (circular orbits containing circular orbits) centered on the Earth (Évora 1993), resulting in the observed patterns of movement (Figure 1).
The Epicycles and Deferent System lasted until the mid-17th century, having undergone only minor modifications and additions, when Copernicus proposed his heliocentric model (Figure 2). Partly motivated by Neoplatonic ideals of beauty, valuing mathematical simplicity and harmony of scientific explanations, Copernicus proposed a model centered on the Sun. The celestial spheres occupied by the planets were ordered in relation to proximity to the Sun, in the familiar sequence Mercury, Venus, Earth , Mars, Jupiter and Saturn, ending in the sphere of the fixed stars.
Copernicus also attributed three types of motion to the Earth: rotation around an axis, translation around the Sun, and variation in the tilt of the axis of rotation. This model not only broke with the geocentric paradigms that had prevailed over the previous thousand years, but was also the first to definitively abandon the distinction between celestial and terrestrial mechanics introduced by Aristotle (Évora 1993). However, it represented “a limited reformulation of planetary theory within the general lines of the accepted structure of Aristotelian science” (Westfall, apud Évora 1993), having initiated a scientific revolution that would be completed by the next generation of astronomers.
Évora, F. R. R. 1993. A revolução copernicano-galileana vol. 1 – Astronomia e cosmologia pré-galileana. 2ª ed. Campinas. UNICAMP, Centro de Lógica, Epistemologia e História da Ciência.
Évora, F. R. R. 1994. A revolução copernicano-galileana vol. 2 – A revolução galileana. 2ª ed. Campinas. UNICAMP, Centro de Lógica, Epistemologia e História da Ciência.