Famous Astronomers: The Life of Galileo Galilei

Among the ranks of the great astronomers, it would be difficult to find one whose life presents more interesting features and remarkable discoveries than Galileo.


Galileo was born in Pisa, Italy, on Feb. 18, 1564. He was the eldest son of Vincenzo de’ Bonajuti de’ Galilei, a Florentine noble. Notwithstanding his illustrious birth and descent, it would seem that the home in which the great philosopher’s childhood was spent was an impoverished one. Young Galileo was likely taught some profession by which he might earn a livelihood.

From his father, Galileo derived a keen taste for music, and it appears that he became an excellent performer on the lute. He was also endowed with considerable artistic power, which he cultivated diligently. Indeed, it would seem that for some time the future astronomer entertained the idea of devoting himself to painting as a profession. His father, however, decided that he should study medicine.

Accordingly, at 17 years old, Galileo had added a knowledge of Greek and Latin to his acquaintance with the fine arts when he entered the University of Pisa. Here, the young philosopher obtained some inkling of mathematics, whereupon he became so interested in this branch of science that he begged to be allowed to study geometry.

The diligence and brilliance of the young student at Pisa did not, however, bring him much credit with the university authorities. In those days, the doctrines of Aristotle were regarded as the embodiment of all human wisdom in natural science, as well as in everything else. It was regarded as the duty of every student to learn Aristotle by heart. Any doubt or questioning of Aristotle’s doctrines was regarded as intolerable presumption.

Young Galileo, however, had the audacity to think for himself about the laws of nature. He would not take any assertion of fact on the authority of Aristotle when he had the means of questioning nature directly as to its truth or falsehood. His teachers thus came to regard him as a somewhat misguided youth, though they respected his unflagging intent to acquire all the knowledge he could.

Galileo’s Life after University
Galileo was appointed, at the age of 25, as Professor of Mathematics at the University of Pisa. Then came the time when he felt himself strong enough to question the old philosophy.

As a necessary part of his doctrine on the movement of bodies, Aristotle had asserted that the time occupied by a stone in falling depends upon its weight, so heavier stones would take less time to fall from a certain height to the Earth. It might have been thought that a statement so easily confuted by the simplest experiments could never have maintained its position in any accepted scheme of philosophy. But Aristotle had said it, and to anyone who ventured to express a doubt the ready sneer was forthcoming, “Do you think yourself a cleverer man than Aristotle?”

Galileo determined to demonstrate in the most emphatic manner the absurdity of this doctrine. The summit of the Leaning Tower of Pisa offered a highly dramatic site for the great experiment. The youthful professor let fall simultaneously from the overhanging top a large heavy body and a small light body. According to Aristotle, the large body ought to have reached the ground much sooner than the small one. But, such was found not to be the case.

In the sight of a large concourse of people, the simple fact was demonstrated that the two bodies fell side by side and reached the ground at the same time. Thus, the first great step was taken in the overthrow of that preposterous system of unquestioning adhesion to dogma, which had impeded the development of the knowledge of nature for nearly 2,000.

Galileo eventually abandoned his chair at the university. The active exertions of his friends then secured his election to the Professorship of Mathematics at Padua, where he went in 1592.

Galileo’s Inventions
In his new position, Galileo began to revolutionize science. Like many other philosophers who have greatly extended our knowledge of nature, Galileo had a remarkable aptitude for the invention of instruments designed for philosophical research. To facilitate his practical work, we find that in 1599 he engaged a skilled workman to live in his house and thus be constantly at hand to build the devices that were ever-springing from Galileo’s fertile brain.

Among the earliest of Galileo’s inventions appears to have been the thermometer, which he constructed in 1602. No doubt this apparatus in its primitive form differed in some respects from the contrivance we call by the same name.

Galileo and the Telescope
The time was now approaching when Galileo was to make that mighty step in the advancement of human knowledge that followed on the application of the telescope to astronomy.

The remarkable properties of the telescope at once commanded universal attention among intellectual men. Galileo received applications from several quarters for his new instrument, of which it would seem that he manufactured a large number to be distributed as gifts to various illustrious personages.

Galileo used the telescope to view celestial bodies, allowing him to inaugurate a new era in astronomy. The first discovery made in this direction appears to have been connected with the number of the stars. Galileo saw to his amazement that through his little tube he could count 10 times as many stars in the sky as his unaided eye could detect. Here was, indeed, a surprise. 

Galileo’s celestial discoveries now succeeded each other rapidly. That beautiful Milky Way, which has for ages been the object of admiration to all lovers of nature, never disclosed its true nature to the eye of man until Galileo turned his telescope on it. The splendid zone of silvery light was then displayed as star dust scattered over the black background of the sky.

However, the greatest discovery made by the telescope in these early days, and perhaps the greatest discovery that the telescope has ever accomplished, was the detection of the system of four satellites revolving around the great planet Jupiter. This phenomenon was so wholly unexpected by Galileo that, at first, he could hardly believe his eyes. However, the reality of the existence of a system of four moons attending the great planet was soon established beyond all question. Numbers of great personages crowded to Galileo to see for themselves this beautiful miniature representing the sun with its system of revolving planets.

After making a number of contributions to astronomy, Galileo died on Jan. 8, 1643.

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Ball, Robert S. (1895). Great Astronomers.