Galileo Galilei

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Galileo Galilei (February 15, 1564 – January 8, 1642) was an Italian scientist and astronomer who supported the (now widely accepted) Copernican theory that the earth revolves around the sun and not vice versa.

He also unintentionally lent his name to the logical fallacy called the Galileo gambit.


This lava flow neatly illustrates Galileo's law of falling bodies.

Galileo discovered Jupiter's four largest moons, known as the "Galilean moons", using his superb homemade telescope.[note 1] Observing moons orbiting around another planet was contrary to the notion the Church held dear — that everything in the universe revolved around the Earth. Galileo discovered other new features; he found that the Sun is not immaculate, as was previously believed, but has sunspots, and discovered mountains and craters on the moon. Galileo discovered that Venus has phases, which was incompatible with the old Ptolemaic geocentric system. He argued that if air resistance is negligible or non-existent, then two bodies dropped from the same height will reach the ground at the same time, regardless of their masses. He proved that bodies, when thrown at an angle, will follow along a parabolic trajectory. After Newton, we know that this, like Kepler's first law, is a consequence of the law of universal gravitation. Galileo formulated the law of the pendulum, but failed to build a time-keeping device before he died. Johannes Kepler and Isaac Newton developed the theory further and provided the scientific underpinning which led to its universal acceptance. Kepler showed that the planets orbit the sun in ellipses rather than perfect circles as previous heliocentrists had thought.

Religious persecution[edit]

And if Your Reverence would read not only the Fathers ... you would find that all agree in explaining literally (ad litteram) that the sun is in the heavens and moves swiftly around the earth, and that the earth is far from the heavens and stands immobile in the center of the universe. Now consider whether in all prudence the Church could encourage giving to Scripture a sense contrary to the holy Fathers...
—Cardinal Bellarmine[1]
The first proposition, that the sun is the centre and does not revolve about the earth, is foolish, absurd, false in theology, and heretical, because [it is] expressly contrary to Holy Scripture; and the second proposition, that the earth is not the centre but revolves about the sun, is absurd, false in philosophy, and heretical, because [it is] expressly contrary to Holy Scripture. The second proposition, that the earth is not the centre but revolves around the sun, is absurd, false in philosophy, and from a theological point of view at least, opposed to the true faith.
—Judgment of the Inquisition

Galileo was forced to recant by the Catholic Inquisition, but famously was alleged to have muttered "E pur si muove" - "And yet, it moves".Wikipedia[note 2] For his recantation, Galileo was not executed as a heretic, but instead sentenced to house arrest for the remainder of his life.[note 3]

Centuries later, it would be pointed out that Pope Clement VII had tried to encourage Copernicus to publish his heliocentric work in 1536,[2] but the work would not be published until after Copernicus' death in 1543… just in time for the Council of Trent. But contrary to what one could expect, the Council of Trent accepted Copernicus' heliocentric system as a mathematical convenience, because it made calendar reform far easier then a geocentric system did.[3] Long criticized for its treatment of Galileo as being anti-science, the Catholic Church now was being portrayed as hypocritical, since a Pope and the Council of Trent had accepted Copernicus' heliocentric system; the concept itself wasn't heretical, though after Galileo, the Church had treated it as such. Finally, in 1992, the Catholic Church expressed regret for how the Galileo affair was handled, though they sidestepped addressing the whole matter of Pope Clement VII and Council of Trent.[note 4]

Later scholarship has stated that, although the Church did reject his arguments, it was over proving his findings, rather than the substance.[4] His forced recanting was over accusations that he had insulted the Pope in his second work, in which he satirized the Pope as a character named "Simplicio," rather than over his theories themselves.[5] In short, he was prosecuted for being the Renaissance version of a troll.

It is a common myth that conservative Christians of the day declined to look through his telescope.[6]

Relationship between Galileo Galilei and Isaac Newton[edit]

Another take on the observation that Newton stood on the shoulders of giants is that, since Galileo Galilei died in January of 1642 and Isaac Newton was born in December of that same year, and since Newton’s work more or less takes over where Galileo’s leaves off, it is the logical, rational thing to conclude that Newton was Galileo reincarnated. This perspective is not adhered to in the scientific community.


I do not feel obliged to believe that the same God who has endowed us with senses, reason, and intellect has intended us to forgo their use and by some other means to give us knowledge which we can attain by them.
—Galileo Galilei.[7]
E pur si muove - "And yet, it moves"
—Galileo Galilei.

See also[edit]

External links[edit]


  1. Simon Marius claimed to have discovered these moons a few days earlier, which Galileo disputed. Though we call them the Galilean satellites, their names — Io, Europa, Ganymede, and Callisto — were Marius's idea. Galileo just called them Jupiter I, Jupiter II, Jupiter III, and Jupiter IV.
  2. There's no evidence that he ever said the phrase at all, and he would have been bloody stupid to have done so.
  3. The fact that he recanted the evidence apparently did not prevent him being punished for even considering it, which some might call thought crime.
  4. Baby steps, baby steps.


  2. Dr. Severyn Żołędziowski (1993) When the Earth Moved Polish Academic Information Center, University at Buffalo
  3. Burke, James (1985) "Infinitely Reasonable" The Day the Universe Changed
  4. Sharratt, Michael. Galileo: Decisive Innovator. (Cambridge University Press, Cambridge, 1994)
  5. Pantin, Isabella. "New Philosophy and Old Prejudices: Aspects of the Reception of Copernicanism in a Divided Europe", Studies in History and Philosophy of Science Part A 30: 237–262
  6. Refusing to look. (2012, August 23). telescope.
  7. In Letter to the Grand Duchess ChristinaWikipedia (1615). Wikiquote.