Galileo Galilei was an Italian physicist and astronomer born in 1564 who made several important astronomical discoveries using his telescope, including the moons of Jupiter, sunspots, and the multitude of stars that make up the Milky Way. He proposed that all objects fall at the same rate regardless of mass, helping develop the scientific method. In 1633, the Catholic Church forced Galileo to recant his support for Copernicus' heliocentric model and placed him under house arrest for the rest of his life.

1. Galileo Galilei MODERN AGE OF ASTRONOMY

2. Quick Facts About Galileo Galilei Galileo Italian physicist and astronomer Birth: February 15, 1564 Death: January 8, 1642 Place of Birth: Pisa, Italy

3. Portrait of Galileo Galilei by Giusto Sustermans

4. Quick Facts About Galileo Galilei Known for: Making a number of important astronomical discoveries, including the four moons of Jupiter, sunspots, and the myriad of stars that compose the Milky Way Proposing that falling bodies would all fall at the same rate, regardless of mass, if there were no air resistance.

5. Quick Facts About Galileo Galilei Milestones: 1589: Taught mathematics at the University of Pisa 1592: Taught mathematics at the University of Padua 1609: Reinvented the telescope based on hearsay of such a device's existence in Holland.

6. University of Padua

7. Quick Facts About Galileo Galilei 1610: Studied the heavens with his telescope, and discovered mountains on the Moon, thousands of stars too faint to be seen unaided, the phases of Venus, and other important astronomical findings 1610: Published several of his astronomical findings in Sidereus Nuncius (The Starry Messenger) 1610: Accepted a position as mathematician and philosopher to the Grand Duke of Tuscany.

8. Quick Facts About Galileo Galilei 1632: Published a defense of the Copernican heliocentric (sun-centered) universe 1633: The Roman Catholic Church forced Galileo to recant his support of the Copernican system, and placed him under lifelong house arrest.

9. Cristiano Banti's 1857 painting Galileo facing the Roman Inquisition

10. Quick Facts About Galileo Galilei Did You Know: Galileo died in 1642, while under house arrest imposed upon him by the Roman Catholic Church. In 1992, the Church acknowledged that its condemnation of Galileo was a mistake. Galileo helped develop the scientific method by using experimentation to test physical theories. Galileo constructed the first thermometer.

11. Galileo’s Experiments in Mechanics Galileo’s greatest contribution were in the field of mechanics. Mechanics is the study of motion and the actions of forces on bodies. He conceptualized that falling bodies of different mass would hit the ground at the same time but on Earth the event described could be affected by air resistance.

12. The Leaning Bell-tower of the Cathedral of Pisa

13. Galileo’s Experiments in Mechanics Galileo discovered laws that invariably described the behavior of physical objects. The most far reaching is the law of inertia. Inertia of a body is that property that of the body that resists any change of motion. If a body is at rest, it tends to remain at rest. Some outside influence is required to start it in motion.

14. Galileo’s Experiments in Mechanics Rest was regarded as the natural state of matter. But Galileo showed that motion is as natural as rest. He reasoned that if an object is slid across a material that is frictionless it would continue to slid on and on. Friction is the resistance encountered by an object moving relative to another object with which it is in contact.

15. Galileo’s Experiments in Mechanics He also thought that force is required to A. slow down B. stop C. speed up D. or change the direction of a moving object. Galileo also studied the way bodies accelerate. There is acceleration when bodies change their speed as they fall freely or roll down inclined planes.

16. Galileo’s Experiments in Mechanics He found that bodies accelerate uniformly. That is, in equal intervals of time they gain equal increments in speed. Galileo formulated these in precise mathematical terms.

17. Galileo and the Heliocentric Cosmology In the 1590’s, Galileo accepted the Copernican hypothesis of the solar system. Earth according to anti-Copernicans should be at rest. But using the idea of inertia, we could imagine an Earth moving perpetually once forced is applied on it.

18. Galileo and the Heliocentric Cosmology He countered the idea of anti-Copernicansthat if Earth were to move it will leave behind objects that are on Earth. Objects on Earth would not be swept off and left behind because they share the Earth’s forward motion.

19. Galileo’s Astronomical Observations In 1609 Galileo made a three power magnification telescope. He got the idea probably from Dutch spectacle maker Hans Lippershey. The best magnification he had was 30. He first tested the accuracy of the image formed in the telescope before using it for astronomical work in 1609.

20. Telescopes Used by Galileo

21. Galileo’s Astronomical Observations In 1610 published the book “The Sidereal Messenger” (Sidereus Nuncius). In this book he presented his discoveries. E.g. Nebulous blurs resolve into many stars like Praesepe cluster in Cancer. Milky Way was made up of multitudes of individual stars.

22. Galileo’s Astronomical Observations He observed that Jupiter had four satellites with revolving periods of about 2 to 17 days. He proved then that Earth is not the only center of motion in the universe. He found that Venus goes through phases just like the moon. This disproves the Ptolemaic system wherein Venus will only have a 45 degree elongation and will only show a crescent phase according to geocentric model.

23. Phases of Venus according to Heliocentric Theory

24. The four Galilean Satellites of Jupiter

25. Galileo’s Astronomical Observations Discovered that the surface of the moon is uneven, rough, full of cavities and prominences that contradicts the long held belief that heavenly bodies are perfect, smooth and incorruptible. Hypothesized that dark areas on the moon are marias or seas.

26. Galileo’s Astronomical Observations He observed blemishes on the Sun that we know now as sun spots. Sun spots are large, comparatively cool areas on the Sun that appear dark because of their contrast with the brighter and hotter solar surface. Galileo observed that spots would move day by day and after some time disappear, and about two weeks same spots would reappear.

27. Galileo’s Drawings of Sun spots

28. Galileo’s Astronomical Observations According to Galileo sunspots could be located either on the surface of the Sun or very close to it. And that these sun spots are carried around by its rotation. He also estimated that Sun’s rotation is a little under a month.

29. Dialogue on the Two Great World Systems Galileo published a book entitled Dialogue on the Two Great World Systems (Dialogo dei Due Massimi Sistemi). The book is a magnificent and unanswerable argument for Copernican astronomy. The characters in the book are: A. Salviati through whom Galileo expresses his ideas. B. Sagredo who is quick to see the truth of Salviati’s arguments. C. and Simplicio who is an Aristotelian philosopher who brings up objections to the Copernican theory.

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