Astronomy as a Science: Galileo and the Telescope

Copernicanism was the target of several criticisms at the end of the 16th century, highlighting the Tycho Brahe’s questions. Brahe was opposed to the gigantic size of the Universe relative to Earth implicit in the Copernicus model (Évora 1994); considered inadmissible the great difference in scale and its main direct consequence: that “all of them [stars] that looked like something bright must be larger than the trajectory or orbit of the Earth […]” (Hyugens 1698 , apud Évora 1994). He proposed his own astronomical system, intermediate to those proposed by Ptolemy and Copernicus, illustrating how the history of scientific thought “is not entirely logical” (Koiré 1973, apud Évora 1994). Concomitantly, others thinkers, including Galileo, continued to use Ptolemaic ideas in their work, keeping the Earth at the center of the Universe and ignoring the new possibilities brought about by the heliocentric model.

Source: 1661 Cellarius’s chart illustrating Copernicus’ heliocentric model of the universe.

It was only at the beginning of the 17th century, with the advent of the telescope as a scientific apparatus, that significant changes in this imagination took place. The precise date of appearance of this instrument is uncertain. According to Évora (1994), the first telescope itself was created by Galileo in 1610, based on a more rudimentary optical instrument created in Holland in 1608 with the purpose of entertaining the court. Galileo, through the method of trial and error, perfected the principles used in the Dutch instrument, creating several instruments before arriving at the ‘final’ version which he presented to Italian intellectuals in 1610, continuing to create devices with progressively greater magnification capacities in subsequent years.

Source: Galileo Galilei is depicted as holding a nail and gazing at diagrams he has scratched on the wall of his prison cell. Underneath a diagram of the Earth orbiting the Sun, he has scratched the words “E pur si muove” (not completely legible in this image).Gerald Delveaux, 2021.

The first observations of the Moon were made by Galileo in 1609, using a instrument with a magnification capacity of about 20 times. They were registered through a series of drawings of the different phases of the star, for the first time revealing its mountainous character. In 1610, the scientist made his first observations of a planet, Jupiter. Also registered in the form of drawings, such observations allowed us to conclude the existence of moons or “planets orbiting the planet” (Évora 1994).

The new information led Galileo to rescue and defend the heliocentric model of Copernicus, as they countered strong criticism directed at him. Even so, they were strongly contested, especially with regard to the instruments used for observation. The lack of understanding of the basic principles of optics and the organization of the Universe itself led to fierce criticism of the observations made with the telescope, since phenomena contrary to common sense were commonplace (Évora 1994).

Noteworthy is the apparently antagonistic behavior of planets and stars when viewed through a telescope; the former seemed to increase while the latter seemed to decrease, or in other words, “[…] the former were brought closer, while the latter saw themselves farther away” (Feyrabend 1970, apud Évora 1994). In response, Galileo refined his observations in subsequent years and developed a new physical theory. Although sometimes little grounded in
anything but logic, therefore approaching more of a philosophical rather than a physical reasoning, laid many of the foundations of scientific thought later used by Kepler and Newton in the development of their respective theories (eg use of mathematics to quantify motion, principle of inertia, etc.). ).


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.

Latest news
Related news


Please enter your comment!
Please enter your name here