2.4 The Birth of Modern Astronomy

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1 2.4 The Birth of Modern Astronomy Telescope invented around 1600 Galileo built his own, made observations: Moon has mountains and valleys Sun has sunspots, and rotates Jupiter has moons (shown): Venus has phases

2 Discovery 2-1: The Foundations of the Copernican Revolution 1. Earth is not at the center of everything. 2. Center of earth is the center of moon s orbit. 3. All planets revolve around the Sun. 4. The stars are very much farther away than the Sun. 5. The apparent movement of the stars around the Earth is due to the Earth s rotation. 6. The apparent movement of the Sun around the Earth is due to the Earth s rotation. 7. Retrograde motion of planets is due to Earth s motion around the Sun.

3 2.4 The Birth of Modern Astronomy Phases of Venus cannot be explained by geocentric model

4 2.5 The Laws of Planetary Motion Kepler s laws were derived using observations made by Tycho Brahe

5 Tycho Brahe

6 Tycho Brahe Tycho Brahe created extensive and detailed observations of the positions of the planets, all with his naked eye! At Uraniborg - part observatory, part palace - Brahe's quadrant that allowed him to measure the positions of planets and stars was 2 metres high and let him measure to an accuracy of 1/360th of a degree - the size of a baseball seen from a mile away.

7 Tycho Brahe Later Brahe realised that the building wasn't stable enough, and he built a new part of his observatory underground, with an armillary sphere even larger than the quadrant - a huge structure of metal rings that let him measure the precise positions of objects in any part of the sky. (A quadrant would only allow measurements of things that were due south.)

8 Tycho Brahe In 1572, Tycho Brahe observes a brilliant supernova (now called SN 1572). At the time, Brahe believed it to be a comet. This supernova proves that it is traveling beyond Earth's atmosphere and therefore provides the first evidence that the heavens can change. Brahe was the man!

9 How Kepler Got His Start Brahe's precise measurements laid the foundation for a new understanding of the motion of the planets. German astronomer Johannes Kepler contacted Brahe at the end of the sixteenth century in an effort to obtain copies of the Danish astronomer's research. Brahe countered with a suggestion that Kepler could work as his assistant, helping him to compile his data.

10 How Kepler Got His Start However, Brahe proved more tightfisted than Kepler had anticipated and refused to share his measurements of the planets and their orbits. Instead, he suggested Kepler work on solving the Mars dilemma that plagued astronomers.

11 How Kepler Got His Start Kepler, using Brahe's detailed observations, realized that the planets moved around the sun not in circles but in stretched out circles known as ellipses. However, the problem took him almost a decade to solve, and Kepler didn't publish it until well after Brahe's death. Although Brahe's family intended to reap as much financial gain as possible from Brahe's observations, Kepler, by his own admission, lessthan-ethically acquired them after Tycho died.

12 Johannes Kepler ( ) Johannes Kepler used mathematics to demonstrate that planetary orbits are elliptical, not circular as in the Ptolemaic theory

13 Kepler s First Law The orbits of the planets are ellipses, with the sun at one focus of the ellipse.

14 Kepler s Second Law The line joining the planet to the sun sweeps out equal areas in equal times as the planet travels around the ellipse.

15 Kepler s Third Law The ratio of the squares of the revolutionary periods for two planets is equal to the ratio of the cubes of their semimajor axes:

16 Kepler s Third Law 61, , Pluto 27, , Neptune 7,060. 7, Uranus Saturn Jupiter Mars Earth Venus Mercury P**2 a**3 P (year) a (AU) Object

17 2.5 The Laws of Planetary Motion 1. Planetary orbits are ellipses, Sun at one focus

18 2.5 The Laws of Planetary Motion 2. Imaginary line connecting Sun and planet sweeps out equal areas in equal times

19 2.5 The Laws of Planetary Motion 3. Square of period of planet s orbital motion is proportional to cube of semimajor axis

20 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

21 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

22 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

23 Galileo ( ) An Italian scientist, Galileo was renowned for his contributions to physics, astronomy, and scientific philosophy. He is regarded as the chief founder of modern science. Galileo was condemned by the Catholic Church for his view of the cosmos based on the theory of Copernicus.

24 Galileo Galilei s Telescope Galileo used the telescope to observe spots on the sun and moon Discredited the Ptolemaic notion that the heavenly bodies are smooth, immaculate, unchanging and perfectly spherical Galileo s drawing of the moon showing craters

25 Galileo Galilei Other achievements: Noticed four of the moons that orbit Jupiter Observed previously unknown distant stars Meant universe is much larger than previously suspected Showed that the velocity of falling bodies depends not on their weight but on the height from which they fall Galileo s telescope However, Galileo was unable to clearly resolve Saturn s rings!

26 Galileo s Books Galileo published his discoveries and support for the Copernican model in two books published in 1616 and Galileo was unusual for the time because he wrote in Italian rather than Latin like most scholars. Galileo also took great pains to make his books interesting often writing them in the form of dialogues rather than dry, boring dissertations. After his first book, "Starry Messenger", was published he was warned by the Church not to publicly support Copernicism again.

27 Galileo Galilei In 1632, he published his Dialogue Concerning the Two Chief World Systems which compares the Copernican and Ptolemaic systems Found guilty of heresy by the Spanish Inquisition and spent the rest of his life under house arrest Galileo s Dialogue

28 Trial Before the Inquisition Galileo abided by this edict until 1632 when he published "A Dialogue on the Two Chief World Systems". This book's outright support for the Copernican model and its ridiculing of the Ptolemaic model earned Galileo a trial before the Inquisition. Galileo was accused of heresy and sentenced to house arrest for life. However, he got off easily compared to fellow Italian Giordano Bruno who was burned at the stake in 1600 for teaching Copernican ideas.

29 In 1992, the Roman Catholic Church finally repealed the ruling of the Inquisition against Galileo. The Church gave a pardon to Galileo and admitted that the heliocentric theory was correct. This pardon came 350 years after Galileo's death.