Galileo Galilei

Galileo GalileiMODERN AGE OF ASTRONOMY

Quick Facts About Galileo Galilei

Galileo Italian physicist and astronomer Birth: February 15, 1564 Death: January 8, 1642 Place of Birth: Pisa, Italy

Portrait of Galileo Galilei by Giusto Sustermans

http://en.wikipedia.org/wiki/Giusto_Sustermans

http://en.wikipedia.org/wiki/File:Justus_Sustermans_-_Portrait_of_Galileo_Galilei,_1636.jpg


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.



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.


University of Padua

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.


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.

Cristiano Banti's 1857 painting Galileo facing the Roman Inquisition

http://en.wikipedia.org/wiki/File:Galileo_facing_the_Roman_Inquisition.jpg

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.


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.


The Leaning Bell-tower of the Cathedral of Pisa


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.


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.


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.


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.

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.

Galileo and the Heliocentric Cosmology

He countered the idea of anti-Copernicans that 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.

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.

Telescopes Used by Galileo


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.


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.

Phases of Venus according to Heliocentric Theory

The four Galilean Satellites of Jupiter


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.


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.

Galileo’s Drawings of Sun spots


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.

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.

Zybrinskie T. BangcadoPrepared by:

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Galileo Galilei