Galileo (1564-1642)Galileo (1564-1642)•An Italian scientist, An Italian scientist,

Galileo was renowned for Galileo was renowned for his contributions to his contributions to physics, astronomy, and physics, astronomy, and scientific philosophy. He scientific philosophy. He is regarded as the chief is regarded as the chief founder of founder of modern modern science. science.

•Galileo was condemned Galileo was condemned by the Catholic Church by the Catholic Church for his view of the for his view of the cosmos based on the cosmos based on the theory of Copernicus.theory of Copernicus.

Galileo Galilei’s TelescopeGalileo Galilei’s Telescope• Galileo used the Galileo used the

telescope to telescope to observe spots on observe spots on the sun and moonthe sun and moon– Discredited the Discredited the

Ptolemaic notion that Ptolemaic notion that the heavenly bodies the heavenly bodies are smooth, are smooth, immaculate, immaculate, unchanging and unchanging and perfectly sphericalperfectly spherical

Galileo’s drawing of the moon showing craters

Galileo GalileiGalileo Galilei• Other achievements:Other achievements:

– Noticed four of the moons Noticed four of the moons that orbit Jupiterthat orbit Jupiter

– Observed previously Observed previously unknown distant starsunknown distant stars

– Meant universe is much Meant universe is much larger than previously larger than previously suspectedsuspected

– Showed that the velocity Showed that the velocity of falling bodies depends of falling bodies depends not on their weight but on not on their weight but on the height from which the height from which they fallthey fall

Galileo’s telescope

However, Galileo was unable to clearly resolve Saturn’s rings!

Galileo’s BooksGalileo’s Books• Galileo published his discoveries and Galileo published his discoveries and

support for the Copernican model in two support for the Copernican model in two books published in 1616 and 1632. books published in 1616 and 1632.

• Galileo was unusual for the time because he Galileo was unusual for the time because he wrote in Italian rather than Latin like most wrote in Italian rather than Latin like most scholars.scholars.

• Galileo also took great pains to make his Galileo also took great pains to make his books interesting often writing them in the books interesting often writing them in the form of dialogues rather than dry, boring form of dialogues rather than dry, boring dissertations. dissertations.

• After his first book, After his first book, "Starry Messenger""Starry Messenger", was , was published he was warned by the Church not published he was warned by the Church not to publicly support Copernicism again. to publicly support Copernicism again.

Galileo GalileiGalileo Galilei

• In 1632, he published In 1632, he published his his Dialogue Dialogue Concerning the Two Concerning the Two Chief World Systems Chief World Systems which compares the which compares the Copernican and Copernican and Ptolemaic systemsPtolemaic systems– Found guilty of heresy Found guilty of heresy

by the Spanish by the Spanish Inquisition and spent Inquisition and spent the rest of his life the rest of his life under house arrestunder house arrest

Galileo’s Dialogue

Trial Before the InquisitionTrial Before the Inquisition

• Galileo abided by this edict until 1632 Galileo abided by this edict until 1632 when he published when he published "A Dialogue on the Two "A Dialogue on the Two Chief World Systems"Chief World Systems". This book's outright . This book's outright support for the Copernican model and its support for the Copernican model and its ridiculing of the Ptolemaic model earned ridiculing of the Ptolemaic model earned Galileo a trial before the Galileo a trial before the InquisitionInquisition. .

• Galileo was accused of heresy and Galileo was accused of heresy and sentenced to house arrest for life. sentenced to house arrest for life. However, he got off easily compared to However, he got off easily compared to fellow Italian fellow Italian Giordano Bruno who was who was burned at the stake in 1600 for teaching burned at the stake in 1600 for teaching Copernican ideas. Copernican ideas.

• In In 19921992, the Roman , the Roman Catholic Church finally Catholic Church finally repealed the ruling of repealed the ruling of the Inquisition against the Inquisition against Galileo. The Church gave Galileo. The Church gave a pardon to Galileo and a pardon to Galileo and admitted that the admitted that the heliocentric theory was heliocentric theory was correct. This pardon correct. This pardon came 350 years after came 350 years after Galileo's death.Galileo's death.

Why are scientists against the Why are scientists against the Ptolemaic Model of the Solar Ptolemaic Model of the Solar

System?System?

• Today, scientists have Today, scientists have evidence of Earth’s evidence of Earth’s orbital motion around orbital motion around the sun. Additionally, the sun. Additionally, the rotation on its axis the rotation on its axis provides seasons, provides seasons, which work against the which work against the early Ptolemaic model.early Ptolemaic model.

On what did Copernicus and Ptolemy agree?

• Both Copernicus’ heliocentric and the Both Copernicus’ heliocentric and the Ptolemaic models agreed on the need for Ptolemaic models agreed on the need for epicycles. These were miniature orbits epicycles. These were miniature orbits that the celestial bodies travelled on as that the celestial bodies travelled on as well as their normal orbits. well as their normal orbits. Copernicus, like Ptolemy, still put these Copernicus, like Ptolemy, still put these bodies orbiting in perfect circles and had bodies orbiting in perfect circles and had to put these in to explain some of the to put these in to explain some of the movements of the planets. movements of the planets.

Long ago, people probably observed the heavens because…

• They used the They used the motion of the motion of the stars to guide stars to guide their their calendars and calendars and to keep track to keep track of time.of time.

The Ptolemaic model of the universe explained planet motions using

• EpicyclesEpicycles – – assuming that assuming that each planet each planet moved on a moved on a small sphere small sphere or circleor circle

• These These Epicycles Epicycles moved around moved around a larger a larger sphere called sphere called a a deferentdeferent

The Ptolemaic model of the universe explained planet motions using

• http://www.polaris.iastate.edu/EveningStar/Unit2/unit2_sub1.htm

What were the many contributions made by Galileo to astronomy using

a telescope?• His contributions to observational His contributions to observational

astronomy include the improving the astronomy include the improving the telescope, telescopic confirmation of telescope, telescopic confirmation of the phases of Venus, the discovery of the phases of Venus, the discovery of the four largest satellites of Jupiter, the four largest satellites of Jupiter, named the Galilean moons in his named the Galilean moons in his honour, and the observation and honour, and the observation and analysis of sunspots. Galileo also analysis of sunspots. Galileo also worked in applied science and worked in applied science and technology, improving compass design. technology, improving compass design.

The Copernican heliocentric model was actually first proposed by:

•The Heliocentric theory The Heliocentric theory was first proposed about was first proposed about 2300 years ago, by 2300 years ago, by Aristarchus of Samos (310-Aristarchus of Samos (310-230 BC). 230 BC).

More Precisely 2-1: Some Properties of Planetary Orbits

Semimajor axis and eccentricity of orbit completely describe it

Perihelion: closest approach to Sun

Aphelion: farthest distance from Sun

2.6 The Dimensions of the Solar System

Astronomical unit: mean distance from Earth to Sun

First measured during transits of Mercury and Venus, using triangulation

2.6 The Dimensions of the Solar System

Now measured using radar:

Ratio of mean radius of Venus’s orbit to that of Earth very well known

Escape Velocity• the speed needed to "break free" the speed needed to "break free"

from the gravitational attraction from the gravitational attraction of a massive body, without of a massive body, without further propulsion, i.e., without further propulsion, i.e., without spending more fuel.spending more fuel.

Must Venus always lie between the Earth and the Sun in the Copernican

theory?• According to the Ptolemaic system, Venus could According to the Ptolemaic system, Venus could

only display a crescent phase because its epicycle only display a crescent phase because its epicycle put it always in between Earth and the sun. put it always in between Earth and the sun.

• The Copernican system put everything rotating around the The Copernican system put everything rotating around the sun, and in this way it explained the phases of Venus.sun, and in this way it explained the phases of Venus.

Geosynchronous Orbits

• Orbit around Earth with orbital Orbit around Earth with orbital period of 1 sidereal day.period of 1 sidereal day.

• Circular Earth geosynchronous Circular Earth geosynchronous orbits have a radius of 42,164 km orbits have a radius of 42,164 km (26,199 mi).(26,199 mi).

• orbits with the same period always orbits with the same period always share the same semi-major axisshare the same semi-major axis

Geosynchronous Orbits

• Orbit around Earth with orbital Orbit around Earth with orbital period of 1 sidereal day.period of 1 sidereal day.

• Circular Earth geosynchronous Circular Earth geosynchronous orbits have a radius of 42,164 km orbits have a radius of 42,164 km (26,199 mi).(26,199 mi).

• orbits with the same period always orbits with the same period always share the same semi-major axisshare the same semi-major axis