It appears to me that they who in proof of any assertion rely simply on the weight of authority, without adducing any argument in support of it, act very absurdly. I, on the contrary, wish to be allowed freely to question and freely to answer you without any sort of adulation, as well becomes those who are in search of truth. - Vincenzo Galilei (Galileo’s father)

Galileo Galilei (1564-1642) In April 1609, a spyglass was made in Paris with a magnification of 3. Galileo pointed this to the heavens. Thus motivated he made an 8 power by August and a 20 power by October.

Galileo’s Office and Instruments

Jupiter has Moons Galileo’s sketches Jupiter’s moons, Io, Europa, Ganymede & Callisto do not orbit the Earth. Galileo’s sketches

It is not the perfect sphere expected in the divine heavens. The Moon is bumpy It is not the perfect sphere expected in the divine heavens. Galileo’s Drawings

Phases of Venus

Ptolemy’s model Venus does not have a full phase as Galileo observed.

Copernicus’ Model: Venus has a full phase.

Galileo’s Astronomical Results Some “planets” don’t orbit the Sun. Venus’ phases contradict Ptolemy’s model. Planets are rocky & mountainous like Earth. The Sun has spots. Saturn has rings. Stars are sprinkled “through the immense abyss of the universe”, not plastered on a crystalline sphere.

Galileo the Heretic In 1632 Galileo published the Dialogue Concerning the Two Chief World Systems in which he advocated the heliocentric (Copernican) view of the Universe. “My dear Kepler, what would you say of the learned here, who, replete with the pertinacity of the asp, have steadfastly refused to cast a glance through the telescope? What shall we make of this? Shall we laugh or shall we cry?” -Letter from Galileo Galilei to Johannes Kepler

Galileo on Trial Galileo was a vocal advocate of the Copernican system. The church ordered him to be silent, but Galileo refused, choosing instead to ridicule the church authorities. He was put on trial, threatened with torture, and made to recant. Thereafter he was kept under house arrest for the remainder of his life. The Catholic Church reopened the Galileo Trial in 1992 and reversed its decision.

Motion: Definitions Distance Need to define two points. Measurement of the interval between points. Units: meters (miles) Velocity Change in distance with time. Vector: has magnitude and direction Units: meters/seconds (miles/hour) Acceleration Change in velocity (direction and/or magnitude) with time Vector Units: meters/seconds2 (miles/hour2)

Galileo contemplating hale Hale stones of different sizes fell at the same speed

Galileo’s Pendulum Experiments Pendulums nearly return to their release heights The period is independent of the bob weight The period is independent of the amplitude The square of the period is proportional to the length Lighter pendulums come to rest faster than heavy ones.

Galileo’s Experiments Need to measure the change of distance with time. Measurement of time: Heartbeat too irregular, Pendulum too awkward, Lute just right. Strings were stretched across the path of the ball close enough to hear a twang. Then they were separated to give twangs at equal intervals. How do objects fall?

Galileo’s findings Objects fall at the same speed independent of mass.* The distance traversed by a falling object increases as the square of the time. This contradicts Aristotle’s theories, which were the still thoughts of the day.